Control method for rechargeable battery packs

Abstract

Even if there is variation in the State of Charge (SOC) of the individual cells in a battery pack, the SOC of the battery pack can be estimated, and whether it will be fully charged or completely discharged can be predicted. [Solution] In a battery pack combining multiple cell batteries CB1 to CB3, the positive electrode ion concentration ratio θ of each cell battery p Next, we estimate the positive electrode ion concentration ratio θ of multiple cell batteries. p The values ​​are plotted on a common θ-axis. The length of the other cells is adjusted according to their capacity to match the length of the selected reference cell cell CBS, which has a capacity of 1, and the positive electrode ion concentration ratio θ of the reference cell cell CBS is plotted. p The positive electrode ion concentration ratio θ of other cell batteries is aligned with the position. p Shift along the θ axis so that the positions coincide. Among each cell battery CB1 to CB3, the positive electrode ion concentration ratio θ with the lowest upper limit voltage is selected. p And the highest lower limit voltage positive electrode ion concentration ratio θ p The SOC of the battery pack is estimated by setting the range between 100% and 0% of the SOC of the battery pack.

Description

[Technical Field]

[0001] This invention relates to a control method for a secondary battery pack, and more specifically, to a control method for a secondary battery pack when there is variation in the state of charge (SOC) of the individual cells constituting the pack. [Background technology]

[0002] Secondary batteries, such as lithium-ion secondary batteries, are suitably used as power sources for BEVs (electric vehicles) and HVs (hybrid vehicles) due to their battery capacity and input / output characteristics. Because high voltage and high current are required for lithium-ion secondary batteries used in vehicle propulsion, they are used as battery packs, combining stacked battery cells. Control of such lithium-ion secondary batteries is based on the State of Charge (SOC) [%]. Therefore, when controlling the charge and discharge of lithium-ion secondary battery packs, it is desirable to perform appropriate control according to the accurate SOC.

[0003] However, while the state of charge (SOC) of a single cell is straightforward, the SOC of a battery pack, unlike that of a single cell, does not have a fixed definition and is defined or estimated using various methods. For example, the charge level estimation device of the invention described in Patent Document 1 includes a charge control unit that stops charging the battery pack when at least one of the multiple batteries in the battery pack satisfies the full charge determination condition. The charge level estimation device is configured to include an estimation unit that sets the SOC[%] of the fully charged battery that satisfies the full charge determination condition to 100[%], and estimates the SOC[%] of the other less-charged batteries from the voltage of the less-charged batteries when charging of the battery pack stops. Therefore, even if there are variations in the charge state and voltage of the multiple batteries in the battery pack, the SOC[%] of each battery can be estimated.

[0004] Furthermore, the information aggregation device of the invention described in Patent Document 2 acquires information regarding the state of charge (SOC) of a cell unit, the terminal voltages of all cell batteries constituting the cell unit, and the charge / discharge current of the cell unit from a battery ECU provided for each cell unit. The information aggregation device estimates the SOC of the battery pack by selection control if the terminal voltages of all cell batteries are within the range between the upper and lower limits. This improves the accuracy of the estimation of the SOC of the battery pack. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2017-198455 [Patent Document 2] Japanese Patent Publication No. 2021-039063 [Patent Document 3] Japanese Patent Publication No. 2024-054481 [Patent Document 4] Japanese Patent Publication No. 2023-085617 [Patent Document 5] Japanese Patent Publication No. 2022-139508 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the secondary batteries that make up a battery pack can degrade at different rates. If the battery pack or the individual cells that make it up are controlled solely by their voltage, it may place a heavy load on some of the individual cells or fail to fully utilize their capacity.

[0007] Therefore, conventionally, the state of charge (SOC) of a battery pack does not move uniformly depending on the SOC position for the same input and output current. In addition, because the SOS of the battery pack is corrected when it hits the upper or lower voltage limits, there was a problem in that it was impossible to predict when it would be fully charged or completely discharged.

[0008] Incidentally, as disclosed in the method for calculating the degree of degradation of a secondary battery described in Patent Document 3, the inventors have proposed a method for calculating the degree of degradation that can estimate the battery capacity even when there are no similar batteries of a relatively undegraded type available, unlike conventional analytical methods.

[0009] Furthermore, as disclosed in the deterioration estimation method of the invention described in Patent Document 4, the applicant has proposed a deterioration estimation device that includes a side reaction current calculation unit that calculates a side reaction current generated at the negative electrode of a secondary battery using the temperature of the secondary battery. It also includes a deterioration index calculation unit that calculates a deterioration index of the secondary battery based on the side reaction current calculated by the side reaction current calculation unit. Therefore, the applicant has proposed a deterioration estimation method that does not restrict the timing of estimating the deterioration of a secondary battery and can reduce the processing load required for estimating the deterioration of a secondary battery.

[0010] Furthermore, as disclosed in the estimation method of the invention described in Patent Document 5, the applicant calculates the solid-phase potential difference and liquid-phase potential difference of the secondary battery, and calculates the voltage error ΔV between the measured voltage value of the secondary battery and the solid-phase potential difference and liquid-phase potential difference of the secondary battery. Next, the estimation device calculates a salt concentration-dependent parameter that minimizes the sum of the reaction overpotential and DC resistance voltage of the secondary battery corresponding to the voltage error ΔV, and identifies the salt concentration corresponding to the calculated salt concentration-dependent parameter based on the correspondence between the salt concentration-dependent parameter and the salt concentration. Then, the estimation device calculates the difference between the identified salt concentration and the initial value of the salt concentration of the secondary battery. Therefore, the applicant has proposed an estimation method that can improve the estimation accuracy of the salt concentration of a secondary battery.

[0011] Based on the above findings, the inventors have arrived at the present invention. The problem that the battery pack control method of the present invention aims to solve is to predict whether the state of charge (SOC) of the battery pack will move uniformly, even when there is variation in the SOC of the individual cells constituting the battery pack, and whether it will reach full charge or complete discharge. [Means for solving the problem]

[0012] To solve the above problems, the battery pack control method of the present invention is characterized in that, in a battery pack combining multiple secondary battery cells, the control device performs the following steps: an ion concentration rate θ estimation step in which the control device estimates the ion concentration rate θ of the active material of one of the electrode plates of the cell cells; a cell cell plotting step in which one of the multiple cell cells is used as a reference cell cell and the ion concentration rates θ of the multiple cell cells estimated in the ion concentration rate θ estimation step are plotted on a common θ axis; a battery capacity correction step in which the length of the other cell cells is adjusted according to the capacity of the cell cells to match the length of the reference cell cell with a capacity of 1; an ion concentration rate θ position adjustment step in which the position of the ion concentration rate θ of the other cell cells is shifted on the θ axis to match the position of the ion concentration rate θ of the reference cell cell on the θ axis; and a battery pack SOC estimation step in which the SOC of the battery pack is estimated by setting the range between the ion concentration rate θ of the lowest upper limit voltage and the ion concentration rate θ of the highest lower limit voltage among the cell cells to 100 to 0[%].

[0013] In this case, in the step of estimating the ion concentration ratio θ of the active material, a solid-phase diffusion model of the secondary battery may be used to calculate the solid-phase voltage difference of the positive electrode and the solid-phase voltage difference of the negative electrode in the thickness direction of the cell battery, the difference between the average ion concentration of the active material and the ion concentration on the surface of the active material may be expressed using a first-order lag model, the ion concentration on the surface of the active material may be derived from the average ion concentration of the active material and the volume-average ion concentration flux of the active material, and the ion concentration ratio θ may be estimated from the average ion concentration on the surface of the active material and the maximum solid-phase ion concentration.

[0014] Furthermore, prior to the ion concentration ratio θ estimation step, a capacity estimation step for estimating the capacity of each electrode plate of the cell battery and a degradation degree estimation step for estimating the degradation degree of the cell battery may be performed.

[0015] Furthermore, after the step of estimating the SOC of the battery pack, a simplified SOC estimation step may be performed in which the SOC is estimated based solely on the ion concentration ratio θ of the reference cell battery. Furthermore, after the step of estimating the SOC of the battery pack, a step of determining abnormal cells may be performed in which, among the individual cells, the SOC estimated based on the ion concentration ratio θ shows a large difference in the change of SOC compared to the other cells, and this is determined to be abnormal.

[0016] Furthermore, prior to the step of estimating the battery pack's SOC, a step of adjusting the cell voltage may be performed, in which the cell with the lowest upper limit voltage among the cell cells is charged, or the cell with the highest lower limit voltage is discharged.

[0017] Furthermore, in the capacity estimation step of estimating the capacity of each cell battery, the process includes: an actual value acquisition process that generates an actual value SOC voltage curve using the measurement results of the open-circuit voltage between 0% and 100% of the SOC[%] for the cell battery; a theoretical value generation process that generates a theoretical value SOC voltage curve calculated from the difference between the theoretical value curve of the positive electrode open-circuit potential calculated from the content of at least one component of the positive electrode composite material of the cell battery using a fitting function and the theoretical value curve of the negative electrode open-circuit potential calculated from the content of at least one component of the negative electrode composite material of the cell battery; and the theoretical value SOC voltage curve and the actual value SOC The following may be performed by computer calculations: an evaluation value calculation process that calculates the evaluation value using an evaluation function that calculates an evaluation value indicating the magnitude of the difference from the voltage curve; and an analysis process that repeatedly performs the theoretical value generation process and the evaluation value calculation process while changing a shift amount parameter that shifts the curve in the SOC direction with respect to at least one of the positive electrode open circuit theoretical value curve and the negative electrode open circuit theoretical value curve in the fitting function, and a scaling rate parameter that adjusts the length of the curve in the SOC direction, and outputs the shift amount parameter that minimizes the evaluation value as the degree of degradation of the cell battery.

[0018] Furthermore, in the step of estimating the degree of degradation of the cell battery, a degradation estimation method for estimating the degradation of the cell battery may be used, which involves using the temperature of the cell battery to calculate the side reaction current generated at the negative electrode of the cell battery, and calculating a degradation index of the cell battery based on the calculated side reaction current.

[0019] Furthermore, this method can be preferably implemented when the electrode plate is the positive electrode. It can also be preferably implemented when the secondary battery is a lithium-ion secondary battery. [Effects of the Invention]

[0020] According to the battery pack control method of the present invention, even if there are variations in the state of charge (SOC) of the individual cells constituting the battery pack, the movement of the SOC of the battery pack is uniform, and it is possible to predict whether it will reach full charge or complete discharge. [Brief explanation of the drawing]

[0021] [Figure 1] This is a block diagram showing the configuration of the control device of this embodiment. [Figure 2] This flowchart shows the procedure for controlling the lithium-ion secondary battery pack according to this embodiment. [Figure 3] This graph illustrates the procedure for estimating the positive electrode capacitance. The graph shown in Figure 3(a) is the SOC-OCV curve (state of charge voltage curve) obtained from measurements. The graph shown in Figure 3(b) shows the positive and negative electrode OCP curves (Open Circuit Potential). [Figure 4] This flowchart shows an example of the processing performed by the degradation estimation program executed by the control unit. [Figure 5] This diagram shows the misalignment of corresponding points between the positive and negative electrodes due to changes in ion concentration on the solid phase surface of the negative electrode caused by the generation of a side reaction current, and the concept of correcting these misalignments. [Figure 6] This figure shows the corrected lower limit lithium ion concentration rate θp and upper limit lithium ion concentration rate θp. [Figure 7] This figure plots the positive electrode ion concentration ratio θp in θ coordinates. [Figure 8] This figure shows the battery capacity correction applied to the positive electrode ion concentration rate θp plotted on the θ coordinate system. [Figure 9] This diagram shows the adjustment of the position of each cell cell to match the positive electrode ion concentration rate θp of the reference cell cell CBS. [Figure 10] This diagram shows the adjustment of the cell battery voltage (S7). [Figure 11] This figure shows the estimated State of Charge (SOC) of the battery pack (S8). [Figure 12] This figure shows the simplified SOC estimation (S9). [Figure 13] This figure shows the abnormal cell battery detection (S11). [Modes for carrying out the invention]

[0022] (Summary of this embodiment) The control method for a battery pack of the present invention will be described below with reference to Figures 1 to 13, using one embodiment of the control method for a lithium-ion secondary battery pack by a control device 10. Note that this embodiment is not limiting to the present invention.

[0023] As explained in the background technology section, there is no established method for evaluating the State of Charge (SOC) [%] of conventional battery packs, and the estimation results have varied. Therefore, the inventors focused on the "ion concentration ratio θ" of one of the electrode plates in the active material, which can be estimated with physical accuracy.

[0024] <Ion concentration ratio θ> Even if the overall open-circuit voltage (OCV) [V] of a battery pack is measured, if there is variation in the characteristics of the individual cell batteries (CB) that make up the battery pack due to degradation, it is difficult to accurately estimate the state of charge (SOC) [%] of the battery pack. Similarly, even if the open-circuit voltage (OCV) [V] of each individual cell battery (CB) that makes up the battery pack is measured, if there is variation in the degradation of each cell battery (CB), it is not possible to accurately estimate the SOC [%] of each individual cell battery (CB).

[0025] Therefore, in order to accurately estimate the SOC [%] of each cell battery CB, we focused on the "ion concentration ratio θ" and estimated the SOC [%] of each cell battery CB. The "active material" in a secondary battery is a material responsible for the occlusion and release of ions in the positive and negative electrodes. During charging, ions are released from the positive electrode active material and occluded in the negative electrode active material through the electrolyte. Also, during discharging, ions are released from the negative electrode active material and occluded in the positive electrode active material through the non-aqueous electrolyte.

[0026] <The positive electrode lithium ion concentration ratio θ of the present embodiment p > In the present embodiment, as an example for the explanation of the present invention, the secondary battery is a lithium ion secondary battery, the ion is lithium ion Li + and the case where the lithium ion concentration in the positive electrode is [mol / m 3 will be described as an example. Note that the secondary battery of the present invention is not intended to be limited to a lithium ion secondary battery and the ion to lithium ion Li + .

[0027] The active material occludes ions. At this time, the ion concentration of the active material is represented by c [mol / cm 3 . The lithium ion concentration on the surface of the active material is represented by c s [mol / cm 3 . The subscript " s " represents the surface of the active material. Also, the average ion concentration of the active material is represented by "c avg [mol / cm 3 . The subscript " avg " represents the average. It is the value obtained by arithmetic-averaging the measured values. Therefore, the average ion concentration on the surface of the active material is represented by "c s,avg [mol / cm 3 . In the positive electrode of the lithium ion secondary battery as in the present embodiment, the average ion concentration on the surface of the active material is represented by "c s,p,avg [mol / cm 3 . Here, the subscript " p " represents the positive electrode. Note that when representing the negative electrode, it is represented by the subscript " n ".

[0028] The maximum solid-phase ion concentration c of metal ions that can be absorbed by each type of active material varies. s,max [mol / cm 3 ] is determined. The maximum solid-phase ion concentration of the positive electrode of the lithium-ion secondary battery in this embodiment is c s,p,max [mol / cm 3 This is indicated by ].

[0029] For example, the positive electrode active material in the lithium-ion secondary battery of this embodiment is lithium ion Li + It is a material capable of intercalating and deintercalating. Specifically, it contains, for example, a lithium transition metal oxide having a layered crystalline structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. Preferably, the transition metal elements contained in the lithium transition metal oxide are at least one of Ni, Co, and Mn. Examples include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickelate (LiNiO2), etc. Furthermore, the positive electrode active material of this embodiment is exemplified by a ternary system called NCM having a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0030] <Ion concentration ratio θ and active material SOC> The inventors have determined the average ion concentration c on the surface of the positive electrode active material in this positive electrode. s,p,avg [mol / cm 3 ] and the maximum solid-phase ion concentration c s,p,max [mol / cm 3 ] From this, the positive electrode ion concentration ratio θ of each cell battery CB p We estimated the [%]. We found that this allowed us to accurately estimate the SOC[%] of the positive electrode.

[0031] <Control method for the battery pack of this embodiment> Based on these findings, the inventors were able to accurately estimate the SOC[%] of the active material of each cell battery CB and define it using a physical quantity, thereby improving the accuracy of the estimation of the SOC[%] of the electrode plates constituting the battery pack. Based on this, it became possible to control the battery pack's SOC[%] so that it changes uniformly, regardless of whether the SOC[%] of the battery pack is in the high or low range, without placing an excessive load on any of the cell batteries CB through overcharging or over-discharging. As a result, it became possible to determine when the battery will be fully charged or completely discharged, allowing for effective control of the battery pack within its capacity without placing an excessive burden on each cell battery CB. The configuration and procedure of the battery pack control method of this embodiment will be described in detail below.

[0032] (Configuration of this embodiment) Figure 1 is a block diagram showing the configuration of the control device 10 in this embodiment. The control device 10 is a device that estimates the State of Charge (SOC) [%] of a lithium-ion secondary battery pack installed in a vehicle. A specific example of the control device 10 is an ECU (Electronic Control Unit) installed in a vehicle.

[0033] The control device 10 comprises a communication interface (I / F) 11, a storage device 12, and an arithmetic unit 13. The communication I / F 11 is an interface for sending and receiving signals between the control device 10 and the lithium-ion secondary battery pack installed in the vehicle, or other devices.

[0034] The storage device 12, regardless of its type (such as ROM or SSD), stores control programs executed by the arithmetic unit 13 and pre-prepared data. It also includes RAM for temporarily storing various types of information processed by the arithmetic unit 13.

[0035] The arithmetic unit 13 is an arithmetic unit such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The arithmetic unit 13 executes the control method defined by the control program by executing the control program stored in the storage device 12.

[0036] The control program includes a measurement value acquisition unit 130, a positive electrode capacity estimation unit 131, a battery degradation degree estimation unit 132, a positive electrode ion concentration estimation unit 133, a battery pack SOC estimation unit 134, a battery pack SOC control unit 135, and an abnormal cell detection unit 136. Note that integrated circuits such as FPGAs (Field-Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits) may execute these program modules.

[0037] The measurement value acquisition unit 130 is a program module that acquires the measured current value, measured voltage value, and measured temperature of a lithium-ion secondary battery. The measurement value acquisition unit 130 can acquire the measured current value of the lithium-ion secondary battery from a current sensor (not shown) that detects the current of the lithium-ion secondary battery via a communication I / F 11. The measurement value acquisition unit 130 can also acquire the measured voltage value of the lithium-ion secondary battery from a voltage sensor (not shown) that detects the voltage of the lithium-ion secondary battery via a communication I / F 11. Furthermore, the measurement value acquisition unit 130 can acquire the measured temperature of the lithium-ion secondary battery from a temperature sensor (not shown) that detects the temperature T[K] of the lithium-ion secondary battery via a communication I / F 11.

[0038] The positive electrode capacity estimation unit 131 estimates the capacity of the positive electrode of each cell battery CB. The battery degradation estimation unit 132 estimates the degree of degradation of each cell battery CB. The positive electrode ion concentration estimation unit 133 calculates the positive electrode ion concentration ratio θ of each cell battery CB. p Estimate [%].

[0039] The battery pack SOC estimation unit 134 determines the positive electrode ion concentration ratio θ of the cell battery CB with the lowest upper limit voltage. p And the highest lower limit voltage positive electrode ion concentration ratio θ p The SOC[%] of the battery pack is estimated by considering the range between 100% and 0% as the SOC[%] of the battery pack.

[0040] Here, the battery pack SOC estimation unit 134 estimates the SOC [%] of the battery pack by performing the following procedure. First, one of the multiple cell batteries CB is designated as the reference cell battery CB, and the positive electrode ion concentration ratio θ of the multiple cell batteries CB that have been estimated is calculated. p These are plotted on a common θ-axis. Next, the lengths of the other cell batteries CB are adjusted according to the capacity of cell batteries CB estimated in the capacity estimation step, with the length of the reference cell battery CBS being set to 1x.

[0041] Then, the positive electrode ion concentration ratio θ of the reference cell battery CBS is located along the θ axis. p The positive electrode ion concentration ratio θ of other cell batteries CB is adjusted to match the position. p The position is shifted along the θ axis to coincide. For each cell battery CB in the θ axis obtained by this procedure, the following procedure is performed. The positive electrode ion concentration rate θ of the lowest upper limit voltage among each cell battery CB. p And the highest lower limit voltage positive electrode ion concentration ratio θ p The SOC[%] of the battery pack is estimated by setting the range between 100% and 0[%] of the battery pack's SOC.

[0042] The battery pack SOC control unit 135 controls the battery pack within the range of 0 to 100% based on the SOC [%] of the battery pack obtained by the procedure described above. The abnormal cell detection unit 136 determines the positive electrode ion concentration ratio θ of each cell battery CB. p Based on this, if the estimated SOC[%] differs significantly from other cell batteries CB due to reasons such as self-discharge, a cell battery CB is deemed abnormal.

[0043] (Procedure of this embodiment) In the lithium-ion secondary battery pack control method of this embodiment, for example, when the operation of the vehicle on which this control method is implemented begins, the control device 10 starts execution of the method. First, the positive electrode capacity is estimated (S1), followed by the battery degradation level (S2). Then, the positive electrode ion concentration ratio θ p It is estimated that (S3).

[0044] Next, the cells CB1 to CB3 are plotted on the θ axis (S4), the battery capacity [Ah] is corrected (S5), and the length of the graph (bars) itself is adjusted according to the battery capacity. Then, the positive electrode ion concentration rate θ p Accordingly, the position of each cell battery CB on the θ axis is adjusted with reference to the reference cell battery CBS (S6). Here, if necessary, the cell battery voltage adjustment step (S7) may be performed prior to the cell pack SOC estimation step (S8). This procedure is not mandatory, but if performed, the cell battery CB with the lowest upper limit voltage is charged and the cell battery CB with the highest lower limit voltage is discharged. Either charging or discharging may be performed. Then, the SOC [%] of the cell pack is estimated (S8). Here, the positive electrode ion concentration rate θ p Based on this, the SOC[%] of the positive electrode is determined, the SOC[%] of each cell battery CB is determined, and the SOC[%] of the entire battery pack is estimated. Then, the vehicle controls the charging and discharging of the battery pack based on this SOC[%] of the battery pack.

[0045] In this embodiment, the positive electrode ion concentration ratio θ p Assuming that it does not change rapidly in a short period of time, the positive electrode ion concentration rate θ p A simplified SOC estimation procedure (S9) is performed, which controls the system by treating the value as a constant value. This procedure is not strictly necessary, but it can reduce the amount of data processing in the vehicle. After a predetermined time has elapsed (S10:YES), abnormal cell battery detection (S11) is performed. Note that abnormal cell battery detection (S11) is not a mandatory procedure and can be performed at any time. Then, for example, when the operation of the vehicle ends, the control method of the battery pack in this embodiment ends (S12:YES, termination).

[0046] The following provides a detailed explanation of each step. <Positive electrode capacity estimation (S1)> This procedure corresponds to an example of the capacity estimation steps of the present invention. However, this does not limit the capacity estimation method of the present invention. Figure 3 is a graph illustrating the procedure for estimating the positive electrode capacity. The graph shown in Figure 3(a) is the SOC-OCV curve (state of charge voltage curve) obtained by measurement. The horizontal axis represents SOC[%] (state of charge), and the vertical axis represents the voltage OCV[V] (open circuit voltage) corresponding to SOC[%]. The graph shown in Figure 3(b) represents the positive and negative electrode OCP curves (open circuit potential). The horizontal axis corresponds to the SOC[%] on the horizontal axis of the graph above. The vertical axis represents the potentials [V] of the positive and negative electrodes.

[0047] As shown in Figure 3(a), the OCV [V] of a lithium-ion secondary battery changes in accordance with the change in SOC [%]. This change is due to the change in the potential [V] of the positive electrode and the potential [V] of the negative electrode during the charge and discharge operation, as shown in Figure 3(b). In a lithium-ion secondary battery, the difference between the potential [V] of the positive electrode and the potential [V] of the negative electrode becomes the OCV [V] between the positive and negative electrode terminals. These positive and negative electrode potentials [V] can be measured as positive electrode OCP [V] and negative electrode OCP [V], respectively. Furthermore, positive electrode OCP [V] and negative electrode OCP [V] can also be logically derived from the active material contained in the composite material coated on each electrode plate.

[0048] Furthermore, as shown in Figure 3(b), the positive electrode OCP[V] extends to the region where the state of charge (SOC) of the cell battery CB is 0[%] or less. This indicates that when the SOC of the cell battery CB is 0[%], the negative electrode has exceeded the amount of lithium it can release, and even when the SOC is 0[%], there is still some lithium that can be accepted on the positive electrode side.

[0049] Furthermore, in Figure 3(b), the negative electrode OCP extends to the region where the SOC is 100% or higher. This indicates that when the SOC of a cell battery CB reaches 100%, the amount of lithium that the positive electrode can release exceeds the limit, and even when the SOC reaches 100%, there is still lithium that can be accepted on the negative electrode side. As will be explained in more detail later, when a lithium-ion secondary battery degrades, the positive electrode OCP[V] changes shape to shift towards the side where the SOC[%] is lower, and the negative electrode OCP[V] changes shape to extend towards the side where the SOC[%] is higher.

[0050] First, in the positive electrode capacity estimation procedure (S1), the measured OCV[V] for lithium-ion secondary batteries between 0[%] and 100[%] is used to perform a measured value acquisition process that generates a graph G1 of the measured SOC voltage curve as shown in Figure 3(a).

[0051] Next, fitting is performed. Fitting first involves a theoretical value generation process that generates a theoretical SOC voltage curve calculated from the difference between graph G2 and graph G3 using a fitting function. Graph G2 is the theoretical value curve of the positive electrode open circuit potential calculated from the content of the positive electrode active material of the lithium-ion secondary battery. Graph G3 is the theoretical value curve of the negative electrode open circuit potential calculated from the content of the negative electrode active material of the lithium-ion secondary battery.

[0052] Next, an evaluation value calculation process is performed to calculate an evaluation value using an evaluation function that calculates an evaluation value indicating the magnitude of the difference between the theoretical SOC voltage curve derived from graphs G2 and G3 and the measured SOC voltage curve shown in graph G1.

[0053] In the fitting function, the shift amount parameter is changed to shift the curve in the SOC direction for at least one of the theoretical value curves of the positive electrode open circuit potential and the theoretical value curve of the negative electrode open circuit potential. Simultaneously, the scaling rate parameter, which adjusts the length of the curve in the SOC direction, is changed. Then, the theoretical value generation process and the evaluation value calculation process are repeated, and the analysis process outputs the shift amount parameter that minimizes the evaluation value as the degradation degree of the lithium-ion secondary battery.

[0054] Referring to Figure 3, the length of graph G2, ΔSOC2, is adjusted while adjusting the left-right displacement ΔSOC1 of graph G3 in Figure 3(b), and this adjustment is repeated until it matches graph G1 shown in Figure 3(a).

[0055] In this fitting, the cell capacity (known or measured, in [Ah] units) corresponds to the capacity CP shown in Figure 3(b). The capacity CP is such that the SOC defined by a specific voltage (in this embodiment, 3.0[V] to 4.1[V]) is in the range of 0 to 100[%]. Since the ratio of ΔSOC1:CP after fitting can be determined numerically, the length ΔSOC2[Ah], which is the capacity of the positive electrode, can be determined.

[0056] The positive electrode capacity estimation (S1) of this embodiment, which is an example of the present invention, is completed by following the procedure described above. Note that the method for estimating the positive electrode capacity in the present invention is not limited to this method, and other methods may be used.

[0057] <Battery degradation estimation (S2)> Next, the degree of battery degradation is estimated (S2). This procedure corresponds to one example of the steps for estimating the degree of battery degradation according to the present invention. However, this does not limit the method for estimating the degree of battery degradation according to the present invention.

[0058] The procedure for estimating the degree of battery degradation (S2) involves the battery degradation estimation unit 132, which is a program of the arithmetic unit 13 of the control device 10, estimating the degradation of the lithium-ion secondary battery. The battery degradation estimation unit 132 is a program that uses the temperature T [K] of the lithium-ion secondary battery to be degraded to calculate the side reaction current [A] generated at the negative electrode of the lithium-ion secondary battery, and calculates a degradation index of the lithium-ion secondary battery based on the calculated side reaction current [A]. The degradation estimation program includes a temperature acquisition unit, a side reaction current calculation unit, an ion concentration calculation unit, a decrease amount calculation unit, a capacity calculation unit, a coating thickness calculation unit, and a coating resistance calculation unit.

[0059] Figure 4 is a flowchart showing an example of the processing of the degradation estimation program executed by the control device 10. The control device 10 repeatedly executes the processing shown in Figure 4 at predetermined sampling intervals.

[0060] In step S21, the temperature acquisition unit can acquire the temperature T[K] of the lithium-ion secondary battery from a temperature sensor (not shown) via the communication I / F11. The temperature acquisition unit acquires the temperature T[K] of the lithium-ion secondary battery at predetermined time intervals. Hereinafter, the time interval at which the temperature acquisition unit acquires the temperature T[K] of the lithium-ion secondary battery will be referred to as the sampling time. The number of times the temperature acquisition unit acquires the temperature T[K] of the lithium-ion secondary battery will be referred to as the sampling count.

[0061] In step S22, the side reaction current calculation unit uses the temperature T[K] of the lithium-ion secondary battery and a predetermined formula to calculate the side reaction current generated at the negative electrode of the lithium-ion secondary battery.

[0062] The side reaction current calculation unit calculates the side reaction current I based on formula (1). SEI Calculate.

[0063]

number

[0064] k is a natural number representing the number of samples. SEI This represents the film thickness of the solid electrolyte interface (SEI) formed on the negative electrode. δ SEI This corresponds to the first film thickness. δ SEI (k-1) is the first film thickness calculated by the film thickness calculation unit described later during the previous sampling. δ SEI,INI represents the initial value of the first film thickness at the solid electrolyte interface. t0 represents the time of the aging treatment applied to the lithium-ion secondary battery. Note that when k=1, δ SEI (0) is the initial value δ SEI,INI This is the result. At this time, ISEI (1) is expressed by formula (2). During the first sampling, the side reaction current calculation unit calculates the side reaction current I shown in formula (2). SEI (1) Calculate (1).

[0065]

number

[0066] The value X shown in equation (1) is a parameter defined in equation (3).

[0067]

number

[0068] M SEI This represents the molecular weight [kg / mol] of the solid electrolyte interface. s,n The specific surface area [cm²] is the ratio of the surface area to the volume of the active material at the negative electrode. 2 / cm 3 ] represents the area of ​​the coated part of the negative electrode [cm²]. 2 ] represents L n ε represents the thickness of the negative electrode [cm]. s,n ρ represents the volume fraction of the negative electrode, which is the ratio of the volume of the active material excluding voids to the volume of the active material including voids. F is the Faraday constant [C / mol]. SEI This is the density of the solid electrolyte interface [kg / cm³]. 3 It represents ].

[0069] The variable Y shown in equation (1) is a parameter determined by the temperature T [K] of the lithium-ion secondary battery, and is defined by equation (4).

[0070]

number

[0071] The value Z shown in equation (1) is a parameter determined by the temperature T [K] of the lithium-ion secondary battery, and is defined by equation (5).

[0072]

number

[0073] Here, we will explain how to derive Y and Z. The time course of the side reaction current at each temperature T[K] (e.g., 60[°C], 70[°C], 75[°C], etc.) is approximated by a power, and a power approximation formula for the side reaction current is derived for each temperature. The period for approximating the time course of the side reaction current can be the aging time and storage period of the lithium-ion secondary battery. Next, the coefficients of the power approximation formula for the side reaction current at each temperature are approximated by a linear equation using an Arrhenius plot. The slope of the obtained approximate linear equation is A in equation (4). coeff This corresponds to B in equation (4). coeff It corresponds to this.

[0074] Furthermore, the exponents of the power approximation formula for the side reaction current at each temperature are plotted on a graph with temperature T [K] on the x-axis and approximated by a straight line. The slope of the obtained approximate straight line is A in equation (5). multi This corresponds to B in equation (5). multi It corresponds to this.

[0075] Parameters Y and Z are determined by the temperature T [K] of the lithium-ion secondary battery. Time t0 is the duration of the aging treatment applied to the lithium-ion secondary battery. Past coating thickness δ SEI This is calculated by the coating thickness calculation unit described later. Initial value δ SEI,INI This is based on the film thickness at the solid electrolyte interface. The side reaction current calculation unit uses parameters Y and Z, time t0, and past film thickness δ, as shown in equation (1). SEI And the initial value δ SEI,INI The side reaction current is calculated based on the following. For example, the side reaction current (I) is calculated using the temperature T [K] of the lithium-ion secondary battery obtained in the second sampling (k=1). SEI (2)) To calculate this, follow the procedure below. The side reaction current calculation unit calculates the film thickness (δ) calculated by the film thickness calculation unit based on the temperature T[K] of the lithium-ion secondary battery obtained in the first sampling. SEI(1)) Using the side reaction current (I SEI (2)) calculate.

[0076] In step S23, the ion concentration calculation unit calculates the current ion concentration on the solid phase surface of the negative electrode using the side reaction current of the negative electrode. The ion concentration calculation unit calculates the current ion concentration on the solid phase surface of the negative electrode based on equations (6) and (7).

[0077]

number

[0078]

number

[0079] Here, c avg This is the average Li concentration of the active material [mol / cm³]. 3 ] represents R p This represents the radius [cm] of the active material particles. s This is the Li concentration on the surface of the active material [mol / cm³]. 3 ] represents D s The diffusion coefficient of Li in the solid phase [cm²] is 2 / s represents j Li SEI This represents the ion flux on the solid phase surface and is defined by equation (8).

[0080]

number

[0081] Here, I SEI This represents the side reaction current. s represents the specific surface area of ​​the active material. F is the Faraday constant [C / mol]. L p L represents the thickness of the positive electrode [cm]. n A represents the thickness of the negative electrode [cm]. A represents the area of ​​the coated part of the negative electrode [cm] 2 It represents ].

[0082] In step S24, the reduction amount calculation unit calculates the amount of decrease in ion concentration on the solid phase surface of the negative electrode using the past ion concentration on the solid phase surface of the negative electrode and the current ion concentration on the solid phase surface of the negative electrode calculated in step S23.

[0083] The decrease amount calculation unit is a program that calculates the decrease in ion concentration on the solid phase surface of the negative electrode using the past ion concentration on the solid phase surface of the negative electrode and the current ion concentration on the solid phase surface of the negative electrode calculated by the ion concentration calculation unit. Specifically, the decrease amount calculation unit can calculate the decrease in ion concentration by subtracting the current ion concentration from the past ion concentration on the solid phase surface of the negative electrode.

[0084] When calculating the decrease in ion concentration for the first time, the past ion concentration on the solid phase surface of the negative electrode is used as the initial value of the ion concentration on the solid phase surface of the negative electrode. When calculating the decrease in ion concentration for the second time or later, the ion concentration on the solid phase surface of the negative electrode calculated in the previous calculation by the ion concentration calculation unit is used as the past ion concentration on the solid phase surface of the negative electrode.

[0085] Generally, when a solid electrolyte interface film grows on an electrode, a side reaction current flows. In this embodiment, it is assumed that the growth of the solid electrolyte interface film is mainly at the negative electrode, and that the side reaction current flows mainly at the negative electrode. In this case, it appears that discharge occurs only at the negative electrode, so the ion concentration on the solid phase surface of the negative electrode decreases.

[0086] <The misalignment of the corresponding points of the positive and negative electrodes, and its correction> Figure 5 shows the shift in the corresponding points of the positive and negative electrodes due to the change in ion concentration on the solid phase surface of the negative electrode caused by the generation of a side reaction current, and a concept for correcting this shift in corresponding points. Figure 5 shows the Open Circuit Potential (OCP) of the positive and negative electrodes before and after the generation of a side reaction current at the negative electrode, and the Open Circuit Voltage (OCV) which corresponds to the difference between these OCPs.

[0087] FIG. 5 shows corresponding points of the positive electrode and the negative electrode indicating the ion concentration and potential of the positive electrode and the negative electrode when the SOC (State Of Charge) is 50% as an example. Before the occurrence of the side reaction current, the ion concentrations indicated by the corresponding points of the positive electrode and the negative electrode are the same. When the side reaction current occurs in the negative electrode, the ion concentration on the solid phase surface of the negative electrode decreases due to discharge, so the corresponding points of the positive electrode and the negative electrode shift. The decrease amount calculation unit calculates the decrease amount of the ion concentration on the solid phase surface of the negative electrode.

[0088] Here, the positive electrode ion concentration rate θ p (the corresponding point on the positive electrode OCP in the figure), and θ n (the corresponding point on the negative electrode OCP in the figure), if the current OCV is lower than the estimated cell OCV, the corresponding point of the negative electrode OCP is shifted to the left. For the appropriately given positive electrode ion concentration rate θ p and θ n , if the current OCV is higher than the estimated cell OCV, it is shifted in the opposite direction. This operation is for deterioration estimation. It means that the degree of deterioration increases as it shifts to the left.

[0089] The positive electrode ion concentration rate θ p is obtained by (1 - current estimated lithium ion concentration (c s,p,avg )) / (maximum lithium ion concentration (c s,p,max )). As a result, the cell OCV curve is deformed, so the corresponding points of θ p -θ n that give a specified voltage (for example, 3.0 [V], 4.1 [V]) are re - taken.

[0090] FIG. 6 is a diagram showing the corrected lower limit positive electrode ion concentration rate θ p and the upper limit positive electrode ion concentration rate θ p . By such a procedure, as shown in FIG. 6, the upper limit positive electrode ion concentration rate θ p and the lower limit positive electrode ion concentration rate θ p can be obtained.

[0091] In step S25, the capacity calculation unit calculates the current capacity [Ah] of the lithium-ion secondary battery using the decrease in ion concentration on the solid phase surface of the negative electrode calculated in step S24.

[0092] The capacity calculation unit is a program that calculates the capacity [Ah] of a lithium-ion secondary battery using the decrease in ion concentration on the solid phase surface of the negative electrode, which is calculated by the decrease amount calculation unit. The capacity calculation unit corresponds to the degradation index calculation unit.

[0093] Specifically, the capacity calculation unit corrects the positive electrode OCP according to the decrease in ion concentration on the solid phase surface of the negative electrode calculated by the decrease amount calculation unit. This correction corresponds to the positive electrode OCP curve shown in Figure 6 shifting to the left. Next, the capacity calculation unit calculates the ion concentration [mol] corresponding to the potential difference between the positive electrode OCP and the negative electrode OCP when SOC is 0[%], and the ion concentration [mol] corresponding to the potential difference between the positive electrode OCP and the negative electrode OCP when SOC is 100[%]. In the example shown in Figure 6, the potential difference between the positive electrode OCP and the negative electrode OCP when SOC is 0[%] is 3.0[V], and the potential difference between the positive electrode OCP and the negative electrode OCP when SOC is 100[%] is 4.1[V]. Then, the capacity calculation unit calculates the difference Li of these ion concentrations. amo By substituting this into formula (9), the capacity of the lithium-ion secondary battery can be calculated.

[0094]

number

[0095] Here, F is the Faraday constant. In this way, the capacity calculation unit can calculate the capacity of the lithium-ion secondary battery after the capacity has decreased due to the generation of a side reaction current at the negative electrode. Alternatively, the capacity calculation unit may calculate the capacity of the lithium-ion secondary battery that has decreased due to the generation of a side reaction current at the negative electrode, that is, the difference between the capacity before the generation of the side reaction current and the capacity after the generation of the side reaction current.

[0096] In the example shown in Figure 6, the OCV curve is set so that the points where the difference between the corrected positive OCP curve and the negative OCP curve is 3.0[V] and 4.1[V] are the endpoints of the corrected OCV curve. However, the corrected OCV curve is not limited to the one shown in Figure 6.

[0097] In step S26, the coating thickness calculation unit calculates the first and second coating thicknesses of the negative electrode. The coating thickness calculation unit is a program that calculates the coating thickness of the solid electrolyte interface formed on the negative electrode using the side reaction current of the negative electrode calculated by the side reaction current calculation unit. Based on equations (10) and (11), the coating thickness calculation unit calculates the coating thickness δ of the solid electrolyte interface of the negative electrode. SEI and film thickness d W Calculate the thickness in [cm]. SEI This represents the film thickness based on the relationship between capacity reduction and side reaction current. Film thickness d W This represents the resistance distance based on the relationship between resistance increase and side reaction current, i.e., the length that contributes to the resistance within the coating. Coating thickness d W This corresponds to the second film thickness.

[0098]

number

[0099]

number

[0100] k is a natural number representing the number of samples. SEI (k) is the negative electrode side reaction current calculated by the side reaction current calculation unit using the temperature T [K] obtained at the kth sampling. δ SEI (k) is the side reaction current I SEI This represents the first coating thickness calculated using (k). δ SEI (k-1) is the side reaction current I based on the temperature T[K] obtained in the k-1 time, i.e., the previous sampling. SEI This represents the first coating thickness calculated using (k-1).W (k) is the side reaction current I SEI This represents the second coating thickness calculated using (k). W (k-1) is the side reaction current I SEI This represents the second coating thickness calculated using (k-1). Note that d W (0) is the initial value (δ) of the second film thickness of the solid electrolyte interface. SEI,INI This corresponds to ). X is a parameter defined by equation (3). Δt represents the sampling time. W(k) is a parameter defined by equation (4) and corresponds to the gain.

[0101]

number

[0102] t0 represents the aging process time applied to the lithium-ion secondary battery. δ SEI (k-1) represents the film thickness of the solid electrolyte interface of the negative electrode, calculated using the side reaction current based on the temperature T[K] obtained in the previous sampling. δ SEI,INI This represents the initial value of the film thickness at the solid electrolyte interface of the negative electrode. X is a parameter defined by equation (3). Y is a parameter defined by equation (4). Z is a parameter defined by equation (5).

[0103] Y W This parameter is determined by the temperature T[K] of the lithium-ion secondary battery and is defined by equation (13).

[0104]

number

[0105] Z W This parameter is determined by the temperature T[K] of the lithium-ion secondary battery and is defined by equation (14).

[0106]

number

[0107] Here, A shown in equation (13) coeff,w and B coeff,w And, as shown in equation (14), A multi,w and B multi,w This section explains how to determine the time-dependent change in the DC internal resistance (DCIR) of a lithium-ion secondary battery over a predetermined period, based on measurement data for DCIR at various temperatures T[K]. For example, measurement data for the DC internal resistance of lithium-ion secondary batteries during storage periods at 60°C, 70°C, 75°C, and 80°C are used. Using this measurement data, the increment from the initial value of the DC internal resistance is calculated for each temperature T[K]. Then, the time-dependent change in the increment of the DC internal resistance at each temperature T[K] is approximated by a power.

[0108] Furthermore, based on the following formula (15), the increment ΔR of the solid electrolyte interface film resistance is calculated. SEI Calculate.

[0109]

number

[0110] Here, R SEI (0) represents the initial value of the DC internal resistance. SEI (k) represents the solid electrolyte interface film resistance and is defined by the following formula (16).

[0111]

number

[0112] k is a natural number representing the number of samples. W (k) is the second coating thickness defined by formula (11). s,n The specific surface area [cm²] is the ratio of the surface area to the volume of the active material at the negative electrode. 2 / cm 3 ] represents the area of ​​the coated part of the negative electrode [cm²]. 2 ] represents L n ε represents the thickness of the negative electrode [cm].s,n This represents the volume fraction of the negative electrode, which is the ratio of the volume of the active material excluding voids to the volume of the active material including voids. SEI This represents the ionic conductivity [S / cm] in the solid electrolyte interface film.

[0113] Therefore, equation (15) is defined as equation (17).

[0114]

number

[0115] Increment ΔR of solid electrolyte interface film resistance SEI It is defined by equation (17). The increment of the DC internal resistance is approximated by a power based on the measured data. Increment of solid electrolyte interface film resistance ΔR SEI This involves calculating the gain W(k) at each temperature T[K] during the storage period of a lithium-ion secondary battery so that the increment of the DC internal resistance matches. Here, the temperature T[K] is, for example, 60[°C], 70[°C], 75[°C], and 80[°C]. Next, the obtained gain W(k) at each temperature T[K] is approximated by powers to derive the power approximation formula for the gain W(k) at each temperature T[K]. Then, the coefficients of the power approximation formula for the gain W(k) at each temperature T[K] are approximated by a straight line using an Arrhenius plot. The slope of the obtained approximate straight line is A in equation (13). coeff,w This corresponds to the intercept of this approximate linear equation, which is B in equation (13). coeff,w It corresponds to this.

[0116] Similarly, the exponents of the power approximation formula for the gain W(k) at each temperature T[K] are plotted on a graph with temperature T[K] on the x-axis and approximated by a straight line. The slope of the resulting approximation line is A in equation (14). multi,w This corresponds to the intercept of this approximate linear equation, which is B in equation (14). multi,w It corresponds to this.

[0117] The coating thickness calculation unit calculates the above A based on formula (13). coeff ,w and B coeffYW is calculated using w and the temperature T [K] of the lithium-ion secondary battery. The coating thickness calculation unit calculates the above A based on formula (14). multi,w and B multi,w And, using the temperature T[K] of the lithium-ion secondary battery, Z W Next, the coating thickness calculation unit calculates the above Y based on formula (12). W and Z W The gain W(k) is calculated using the formula (11). Then, the film thickness calculation unit uses the gain W(k) to calculate the second film thickness d of the solid electrolyte interface of the negative electrode. W Calculate.

[0118] In step S27, the coating resistance calculation unit calculates the second coating thickness d of the solid electrolyte interface of the negative electrode, which was calculated by the coating thickness calculation unit. W The solid electrolyte interface film resistance [Ω] is calculated using the following formula. The film resistance calculation unit calculates the solid electrolyte interface film resistance R based on formula (16). SEI It can be calculated.

[0119] <Positive electrode ion concentration θ> p Estimate (S3)> Next, the positive electrode ion concentration ratio θ p The estimation (S3) is performed. This procedure corresponds to an example of the steps for estimating the ion concentration rate θ of the present invention. However, this does not limit the method for estimating the ion concentration rate θ of the present invention. As described above, the ion concentration rate θ is estimated in the procedure for estimating the degree of battery degradation (S3), but here the ion concentration rate θ is estimated without considering the thickness of the film at the solid electrolyte interface (SEI).

[0120] The positive electrode ion concentration estimation unit 133 can calculate the solid-phase voltage difference of the positive electrode and the solid-phase voltage difference of the negative electrode in the thickness direction of the lithium-ion secondary battery, respectively, using a solid-phase diffusion model of the lithium-ion secondary battery.

[0121] Equation (18) is a solid-phase diffusion equation, which is an example of a solid-phase diffusion model.

[0122]

number

[0123] Here, "c" represents the lithium ion concentration of the active material [mol / m³] 3 It represents ]. "t" represents time.

[0124] "r" represents the position of the active material in the particle diameter direction. "D s " is the diffusion coefficient of lithium ions in the solid phase [m 2 This represents / s] Equation (19) shows the boundary conditions for the solid-phase diffusion model in equation (18).

[0125]

number

[0126] Here, "c s " is the lithium ion concentration on the surface of the active material [mol / m³ 3 It represents ]. "R p This indicates the surface position of the active material in the particle diameter direction.

[0127] "j Li " is the lithium ion flux [mol / m 2 It represents [s]. The solid-phase diffusion model shown in equation (18) approximates the lithium ion concentration distribution in the active material with a four-dimensional polynomial, and the average lithium ion concentration of the active material "c avg " and the lithium ion concentration on the surface of the active material "c s This can be derived by representing the difference with a first-order lag model.

[0128] Average lithium ion concentration of active material "c avg 」[mol / m 3 ] can be expressed using formula (20).

[0129]

number

[0130] Volume-average lithium ion concentration flux q [mol / m³] of the active material 3 ·m] can be expressed using formula (21).

[0131]

number

[0132] Lithium ion flux "j Li This can be expressed using formula (22).

[0133]

number

[0134] Here, "I" represents electric current. "a s " is the surface area (specific area) of the active material per unit volume [1 / m] This can be expressed using formula (7).

[0135] "F" is Faraday's constant. "L p " represents the thickness [m] of the positive electrode. "L n " represents the thickness of the negative electrode [m].

[0136] "A" is the reaction area of ​​the electrode [m²] 2 It represents ]. By following the above procedure, the lithium ion concentration "c" on the surface of the active material is obtained. s This can be expressed using formula (23).

[0137]

number

[0138] Here, the positive electrode ion concentration ratio θ pThis is the solid-phase lithium concentration c of the positive electrode. s,p [mol / cm 3 ] and the maximum solid-phase ion concentration c s,p、max [mol / cm 3 ] can be obtained from formula (24). In this embodiment, c s,p,avg [mol / cm 3 ] to c s,p It is being used as such. s,p,max [mol / cm 3 ] is the maximum solid-phase ion concentration of the positive electrode. s,p、max " is a physical property value determined by the positive electrode active material. Also, "c s,p,avg [mol / cm 3 ]" is the solid-phase average lithium concentration of the positive electrode. According to formula (23), the lithium ion concentration "c" on the active material surface of the positive electrode is calculated. s [mol / cm 3 It leads to ].

[0139]

number

[0140] <Plotting cell battery CB on the θ axis (S4)> First, the positive electrode ion concentration ratio θ of each cell battery CB. p The positive electrode ion concentration ratio θ is plotted on the θ axis (S4). This procedure corresponds to an example of the steps for plotting the cell battery of the present invention. Below, the positive electrode ion concentration ratio θ p The method using this will be described. In this embodiment, the positive electrode will be used as an example, but the same calculation can be performed for the negative electrode by simply reversing the left and right sides. That is, at the positive electrode, when the positive electrode SOC = 100[%], the positive electrode ion concentration ratio θ p = 0, but at the negative electrode, when negative electrode SOC = 0[%], the negative electrode ion concentration θ n = 0.

[0141] Figure 7 shows the positive electrode ion concentration ratio θ in θ coordinates. p This is a plotted diagram. Here, the θ coordinate represents the position of the ion concentration rate θ on a straight line. p" is defined as "1 - positive electrode Li concentration / maximum Li concentration", and is the ratio (0 to 1) defined by the formula shown in the above formula (6). The upper limit positive electrode ion concentration rate θ shown in FIG. 6 p , the lower limit positive electrode ion concentration rate θ p is plotted on the θ coordinate.

[0142] In FIG. 7, the positive electrode ion concentration rate θ p = 0 is set as the lower limit voltage of 3.0 [V], and the positive electrode ion concentration rate θ p = 1 is set as the upper limit voltage of 4.1 [V] and shown. Here, the positive electrode active material SOC can be represented by the above-described positive electrode ion concentration rate θ p . At this point, it is shown that the positive electrode ion concentration rate θ p of each cell battery CB1 to CB3 and their respective SOC [%] correspond one-to-one.

[0143] In the present embodiment, the actual assembled battery is composed of a large number of cell batteries CB. For the sake of convenience, a plurality of cell batteries CB are simplified and described by three cell batteries CB1 to CB3. Also, any one of the cell batteries CB is set as the "reference cell battery CBS". The reference cell battery CBS is a cell battery CB that serves as a reference for adjustment when comparing a plurality of cell batteries CB, and any cell battery CB can be selected for the sake of convenience. In the present embodiment, the cell battery CB1 is described as the reference cell battery CBS. Here, the strip-shaped display of each cell battery CB1 to CB3 shown in FIG. 7 is conveniently referred to as a "bar".

[0144] <Battery capacity correction (S5)> Next, battery capacity correction (S5) is performed on the θ coordinate. This procedure corresponds to an example of the battery capacity correction step of the present invention.

[0145] FIG. 8 is a diagram showing battery capacity correction for the positive electrode ion concentration rate θ p plotted on the θ coordinate. The length of each bar is adjusted according to the ratio of each cell of the positive electrode capacity of each cell battery CB1 to CB3. Here, the "positive electrode capacity" refers to the positive electrode capacity obtained in the procedure of positive electrode capacity estimation (S1) or the positive electrode capacity corrected by the degree of deterioration obtained in battery deterioration degree estimation (S2).

[0146] The length of each bar is enlarged or reduced so that the reference cell battery CBS (in this case, cell battery CB1) is set to 1x. At this point, the positive electrode ion concentration ratio θ on the θ axis is calculated. p The correspondence between and SOC[%] will no longer be one-to-one.

[0147] In this embodiment, we assume that the positive electrode capacity of cell cell CB2 is 1.1 times that of cell cell CB1, and the positive electrode capacity of cell cell CB3 is 0.9 times that of cell cell CB1. In this case, the θ-axis coordinate to be used as the reference is the θ-axis coordinate of cell cell CB1, which is the reference cell cell CBS. The length of this bar represents the positive electrode ion concentration ratio θ of the reference cell cell CBS. p The adjustment is made using the =0 position as a reference. Specifically, the length of cell cell CB2 is set to 1.1 times that of cell cell CB1, and the length of cell cell CB3 is set to 0.9 times that of cell cell CB1. At this time, the left ends of the bars for each cell cell CB1 to CB3 are aligned to the same position. By adjusting the length of these bars, the SOC[%] and positive electrode ion concentration ratio θ of each cell cell CB1 to CB3 are determined. p Because the values ​​will deviate from the reference cell battery CBS, the values ​​other than the reference cell battery CBS will have no physical meaning.

[0148] <Positive electrode ion concentration θ> p Adjust position accordingly (S6)> Next, the positive electrode ion concentration θ of the reference cell battery CBS. p The positions of each cell battery CB2 and CB3 are adjusted accordingly (S6). This procedure corresponds to an example of the steps for adjusting the ion concentration ratio θ position of the present invention.

[0149] Figure 9 shows the positive electrode ion concentration θ of the reference cell battery CBS. p This diagram shows the adjustment of the positions of each cell battery CB1 to CB3 accordingly. The battery capacity correction (S5) procedure determines the positive electrode ion concentration ratio θ. p The position is shifted. Therefore, the positive electrode ion concentration ratio θ of the reference cell battery CBS is p Adjust the positions of each cell battery, CB2 and CB3, to match the position of the cell.

[0150] Specifically, the positive electrode ion concentration ratio of cell battery CB2 is θ p Since it was = 0.616, the positive electrode ion concentration ratio θ of the reference cell battery CBS p To match =0.46, shift the bar for cell battery CB2 to -0.156, or 0.156 to the left. Then, the positive electrode ion concentration ratio θ of cell battery CB2. p The position = 0.46 corresponds to the positive electrode ion concentration rate θ of the reference cell battery CBS. p Align it to the position =0.46. Then, the positive electrode ion concentration ratio θ will be at the upper voltage limit = 4.1[V]. p =0.198 is the positive electrode ion concentration ratio θ p = 0.042. Also, the positive electrode ion concentration ratio θ at the lower limit voltage = 3.0[V] p =0.946 is the positive electrode ion concentration ratio θ p This equals 0.79.

[0151] The positive electrode ion concentration ratio of cell battery CB3 is θ p Since it was = 0.594, the positive electrode ion concentration ratio θ of the reference cell battery CBS was p To match =0.46, shift the bar for cell battery CB2 by -0.134, or 0.134 units to the left. Then, the positive electrode ion concentration ratio θ of cell battery CB3. p The position = 0.46 corresponds to the positive electrode ion concentration rate θ of the reference cell battery CBS. p Align it to the position =0.46. Then, the positive electrode ion concentration ratio θ will be at the upper voltage limit = 4.1[V]. p =0.126 is the positive electrode ion concentration ratio θ p = 0.008. Also, the positive electrode ion concentration ratio θ at the lower limit voltage = 3.0[V] p =0.81 is the positive electrode ion concentration ratio θ p This equals 0.676.

[0152] <Cell battery voltage adjustment (S7)> Figure 10 shows the adjustment of the cell battery CB voltage (S7). Next, the voltage of the cell battery CB is adjusted (S7). This procedure corresponds to an example of the steps for adjusting the cell battery voltage according to the present invention.

[0153] In the battery pack SOC estimation (S8) described later, the SOC of the battery pack is considered to be between 0 and 100% between the lower limit voltage [V] of the highest cell battery CB and the upper limit voltage [V] of the lowest cell battery CB, and the battery pack is controlled accordingly.

[0154] Here, if the lower limit voltage [V] of the highest cell CB is lower and the upper limit voltage [V] of the lowest cell CB is higher, the range of the battery pack's SOC from 0 to 100 can be expanded.

[0155] Therefore, the positive electrode ion concentration ratio θ p After position adjustment (S6), the cell cell CB with the highest lower limit voltage [V] among cell cells CB1 to CB3 is charged. The cell cell CB with the lowest upper limit voltage [V] is discharged. This process determines the positive electrode ion concentration ratio θ of the cell cell CB with the highest lower limit voltage [V]. p The value decreases. Also, the positive electrode ion concentration ratio θ of the lowest cell battery CB upper voltage [V] p This increases. As a result, the gap between the lower limit voltage [V] of the highest cell CB and the upper limit voltage [V] of the lowest cell CB widens. In other words, the charge and discharge range of the battery pack widens.

[0156] Note that this procedure is not necessarily required. Alternatively, you may set a threshold for determining when to perform this step. Furthermore, if, after the first charge or discharge, the cell cell CB with the highest lower limit voltage or the cell cell CB with the lowest upper limit voltage becomes a different cell cell CB, this procedure may be repeated.

[0157] <Battery SOC estimation (S8)> Once the voltage adjustment of the cell battery CB is complete (S7), the state of charge (SOC) of the battery pack is estimated (S8). This procedure is an example of the steps for estimating the SOC of a battery pack according to the present invention.

[0158] Figure 11 shows the estimated state of charge (S8) of the battery pack. In the state shown in Figure 9, if the voltage of cell battery CB was not adjusted (S7), the positive electrode ion concentration ratio at the highest cell battery CB1 upper limit voltage of 4.1[V] would be θ p = 0.16. Also, the positive electrode ion concentration ratio at the lowest lower limit voltage of cell battery CB1, 3.0[V], is θ p = 0.676. And this θ p = 0.16 and θ p The usable range for the battery pack is between θ = 0.676 (A). That is, this θ p =0.16 becomes the SOC=100[%] of the battery pack, θ p =0.676 corresponds to the SOC=0[%] of the battery pack. Furthermore, replacing (A) with Ah gives the full charge capacity [Ah] of the battery pack. In this case, the SOC[%] of the battery pack can be calculated as follows: (State of Charge of the battery pack) = (B) / (A) =(0.46-0.676) / (0.16-0.676)×100 ≒42[%] Based on the procedure described above, from positive electrode capacity estimation (S1) to battery pack SOC estimation (S8), the SOC[%] of the battery pack is estimated, and the charging and discharging of the battery pack is controlled based on this SOC[%] value.

[0159] <Simple SOC estimation (S9)> As described above, the State of Charge (SOC) of the battery pack is estimated by the procedure from positive electrode capacity estimation (S1) to battery pack SOC estimation (S8), and the charging and discharging of the battery pack is controlled based on this SOC value. However, in order to simplify the process, reduce the control burden, and speed up the process, this embodiment includes a simplified SOC estimation procedure (S9). This procedure corresponds to an example of the simplified SOC estimation steps of the present invention.

[0160] Figure 12 shows the simplified SOC estimation (S9). For short periods, the battery capacity and degradation of each cell CB1 to CB3 are small, and the positive electrode ion concentration θ of each cell CB1 to CB3 is small. pThe changes are approximately synchronized. That is, in a short period of time, with little deviation in the cell batteries CB1 to CB3, as shown in FIG. 12, the positive ion concentration rate θ p changes by the same amount and moves left and right by the same amount. Therefore, for a while, only the SOC of the cell battery CB1 is estimated, and for the other cell batteries CB2 and CB3, they are considered to have the same changes as the cell battery CB1. As a result, the calculation amount of the SOC estimation can be reduced, and the control can be speeded up.

[0161] The procedure of the simple SOC estimation (S9) is repeated until a predetermined time (for example, 60 [sec]) elapses (S10: NO), and when the predetermined time elapses (S10: YES), it ends. <Abnormal cell battery determination (S11)> When the predetermined time elapses (S10: YES) and the procedure of the simple SOC estimation (S9) ends, the procedure of the abnormal cell battery determination (S11) is performed. This procedure corresponds to an example of the step of the abnormal cell battery determination of the present invention.

[0162] FIG. 13 is a diagram showing the abnormal cell battery determination (S11). As described above, in a short period of time, the battery capacity and deterioration of each of the cell batteries CB1 to CB3 are small, and the changes in the positive ion concentration rate θ p of each of the cell batteries CB1 to CB3 are approximately synchronized. However, as shown in FIG. 13, when the change in the positive ion concentration rate θ p of a specific cell battery CB (here, the cell battery CB2) becomes larger compared to the positive ion concentration rate θ p of other cell batteries CB, it is assumed that self-discharge or the like is the cause. Therefore, when the change in the positive ion concentration rate θ p of a specific cell battery CB becomes larger compared to the positive ion concentration rate θ p of other cell batteries CB, and in the figure, when it is shifted to the right, it is determined that an abnormality has occurred in the cell battery CB2.

[0163] <Whether it is the end (S12)> For example, the control method of this embodiment terminates (S12:YES) when the vehicle operation is terminated, or when an abnormality is detected in the abnormal cell battery detection (S11). Otherwise (S12:NO), the control method of this embodiment is repeated. In this case, it is not necessarily required to return to positive electrode capacity estimation (S1) as shown in Figure 2; for example, the positive electrode ion concentration ratio θ p You may also return to the estimation (S3) procedure.

[0164] (Operation of this embodiment) In this embodiment, the positive electrode ion concentration ratio θ of the positive electrode active material of each cell battery CB p The absolute state of each cell battery CB is evaluated using the following: Then, the positive electrode ion concentration ratio θ p We will use this to compare the SOC[%] of each cell battery CB.

[0165] Based on this premise, it is possible to control the SOC[%] of the battery pack so that it changes uniformly, whether the SOC[%] of the battery pack is in the high or low range, without placing a heavy load on or unnecessarily restricting any particular cell battery CB. As a result, it is possible to determine when the battery will be fully charged or completely discharged, which allows for effective control of the battery pack within its capabilities without placing an excessive burden on each cell battery CB.

[0166] (Effects of this embodiment) (1) According to the battery pack control method of the present invention, even if there is variation in the state of charge (SOC) of the cell batteries CB constituting the battery pack, the movement of the SOC of the battery pack will be uniform for the same input / output current. In addition, it has the effect of being able to predict whether the battery will be fully charged or completely discharged.

[0167] (2) In the battery pack control method of this embodiment, the control device 10 estimates the positive electrode ion concentration θ of the positive electrode active material of each cell battery CB1 to CB3 in the step of estimating the ion concentration θ. p To estimate this, each cell battery CB1 to CB3 is set to the positive electrode ion concentration θ. pThis has the effect of allowing for accurate evaluation using a specific physical quantity.

[0168] (3) Of the multiple cell batteries CB1 to CB3, cell battery CB1 is used as the reference cell battery CBS, and the estimated positive electrode ion concentration rate θ p Based on the positive electrode ion concentration ratio θ of each cell battery CB2 and CB3 p The values ​​are plotted on a common θ-axis. Therefore, multiple cell batteries CB1 to CB3 are plotted on the positive electrode ion concentration θ. p This has the effect of allowing comparisons based on [a certain factor].

[0169] (4) The length of the other cells CB2 and CB3 is adjusted according to the capacity of cell CB, so that the length of the reference cell CBS is set to 1x. For this purpose, the positive electrode ion concentration ratio θ of the positive electrode active material of multiple cells CB1 to CB3 p This has the effect of allowing comparisons that reflect the battery capacity.

[0170] (5) The positive electrode ion concentration ratio θ of the reference cell cell CBS in the θ axis p The positive electrode ion concentration ratio θ of the other cell batteries CB2 and CB3 is adjusted according to their positions. p The positions are shifted along the θ axis to coincide. Therefore, the positive electrode ion concentration ratios θ of multiple cell batteries CB1 to CB3 are shifted. p This has the effect of allowing for accurate comparison.

[0171] (6) Among the multiple cell batteries CB1 to CB3, the ion concentration ratio θ with the lowest upper limit voltage p and the ion concentration ratio θ of the highest lower limit voltage p The SOC of the battery pack is estimated by setting the range between 100% and 0% of the SOC of the battery pack. This has the effect of not placing an excessive burden on any of the multiple cell batteries CB1 to CB3, and controlling the charging and discharging of the battery pack in the most efficient way.

[0172] (7) The positive electrode ion concentration ratio θ of the positive electrode active material pIn the step of estimating the ion concentration ratio θ, a solid-phase diffusion model of a lithium-ion secondary battery is used to calculate the solid-phase voltage difference of the positive electrode and the solid-phase voltage difference of the negative electrode in the thickness direction of the battery. The difference between the average ion concentration of the active material and the ion concentration on the surface of the active material is represented by a first-order lag model. The ion concentration on the surface of the active material is derived from the average ion concentration of the active material and the volume-average ion concentration flux of the active material. The ion concentration ratio θ is estimated from the average ion concentration on the surface of the active material and the maximum solid-phase ion concentration.

[0173] Therefore, the positive electrode ion concentration ratio θ of the positive electrode active material of multiple cell batteries CB1 to CB3 is precisely determined. p This has the effect of allowing us to estimate [something]. (8) Positive electrode ion concentration ratio θ p Prior to the estimation step, a capacity estimation step is performed to estimate the capacity of the electrode plates of each cell battery CB1 to CB3, and a degradation degree estimation step is performed to estimate the degree of degradation of the cell battery CB. For this purpose, the positive electrode ion concentration ratio θ of each cell battery CB1 to CB3 is performed. p This has the effect of accurately estimating the capacity of the electrode plates of each cell battery CB1 to CB3 and the degree of battery degradation. Furthermore, this invention can be implemented even with lithium-ion secondary batteries that have a history of use in vehicles.

[0174] (9) After the step of estimating the SOC of the battery pack, the positive electrode ion concentration ratio θ of the reference cell battery CBS. p A simplified SOC estimation step is performed, which estimates the SOC based solely on the following: This has the effect of processing the SOC[%] of the battery pack quickly and with minimal processing burden.

[0175] (10) Of each cell battery CB1 to CB3, the positive electrode ion concentration ratio θ p Based on the estimated State of Charge (SOC), a step is performed to determine if a cell cell CB is abnormal if its SOC change is significantly different from that of other cell cells CBs. This has the effect of detecting abnormal cell cells CBs caused by self-discharge, etc.

[0176] (11) Prior to the step of estimating the state of charge (SOC) of the battery pack, a cell voltage adjustment step is performed in which the cell CB with the lowest upper limit voltage among the cell cells CB1 to CB3 is charged, or the cell CB with the highest lower limit voltage is discharged. This has the effect of expanding the control range of the battery pack and enabling efficient use of the battery pack.

[0177] (12) In the capacity estimation step, in which the capacity of the electrode plates of each cell battery CB is estimated, the measured value acquisition process is performed and a theoretical SOC voltage curve is generated from the difference between the theoretical value curve of the positive electrode open circuit potential and the theoretical value curve of the negative electrode open circuit potential using a fitting function. An evaluation value is calculated using an evaluation function that calculates an evaluation value indicating the magnitude of the difference between the theoretical value SOC voltage curve and the measured value SOC voltage curve. The shift amount parameter that minimizes the evaluation value while changing the shift amount parameter and the scaling rate parameter is output as the degree of degradation of the cell battery.

[0178] Therefore, the positive electrode ion concentration ratio θ p This has the effect of being able to accurately estimate the capacity of the electrode plates of each cell battery CB, which is the premise for the estimation. (13) In addition, in the degradation estimation step to estimate the degree of degradation of the cell battery CB, the secondary battery temperature T [K] is used to calculate the side reaction current generated at the negative electrode of the cell battery CB. Based on the calculated side reaction current, a degradation index of the cell battery CB is calculated. For this purpose, the positive electrode ion concentration ratio θ p This has the effect of being able to accurately estimate the degradation of each cell battery CB, which is the premise for the estimation.

[0179] (14) The control method for the battery pack of this embodiment has the advantage of being suitably implemented when the electrode plate is the positive electrode and the secondary battery is a lithium-ion secondary battery, as shown in this embodiment.

[0180] (Alternative example) The present invention is not limited to this embodiment and can be implemented in the following forms. ○In this embodiment of the battery pack control method, we have exemplified a battery pack that constitutes a battery pack installed for propulsion in an electric vehicle or a hybrid vehicle mounted on a vehicle, but the application is not limited as long as it is a battery pack made by combining cell batteries CB.

[0181] ○In addition, in this embodiment, the lithium ion Li of the positive electrode of the lithium-ion secondary battery + This was given as an example. However, it is not limited to this, and the term can be broadly applied to secondary batteries that are composed of multiple cells, such as other non-aqueous electrolyte secondary batteries, alkaline electrolyte secondary batteries like NiMH batteries, and all-solid-state batteries.

[0182] ○In this embodiment, the capacity estimation step, which estimates the capacity of the electrode plates of each cell battery CB, and the degradation degree estimation step, which estimates the degree of degradation of the cell battery CB, are performed in separate procedures. However, these may be combined into a single procedure. In short, the objective of this invention is achieved if it is possible to analyze the capacity taking degradation into account.

[0183] ○Also, the positive electrode ion concentration ratio θ at the positive electrode p As explained using the example, the negative electrode ion concentration ratio θ at the negative electrode n It can also be carried out using [this method]. In this case, when the open-circuit voltage OCV [V] of the battery pack increases, lithium ion Li [V] will be released at the negative electrode. + The negative electrode ion concentration ratio θ is absorbed into the negative electrode active material. n The positive electrode ion concentration ratio θ increases in the θ coordinate shown in Figures 7-13. p This results in a movement that is reversed left to right.

[0184] ○In this embodiment, three cell batteries CB1 to CB3 are used as examples for illustrative purposes, but the number of cell batteries is not limited to three; in reality, a battery pack may contain many cell batteries CB.

[0185] ○The control device 10 shown in Figure 1 is just one example, and its configuration is not limited as long as the procedure of the present invention can be carried out. For example, the processing may be determined outside the vehicle by means of communication. ○The flowcharts shown in Figures 2 and 4 are examples of implementation of the present invention, and it goes without saying that those skilled in the art can implement it by adding, deleting, rearranging, or modifying the procedures.

[0186] ○For example, in the flowchart shown in Figure 2, if it is determined that the process will not terminate (S12:NO), the system returns to positive electrode capacity estimation (S1), but it is also possible to control the system to return to battery degradation estimation (S2). Furthermore, in either procedure, the decision of whether or not to execute the process may be made based on predetermined thresholds such as elapsed time, SOC[%], and ion concentration ratio θ.

[0187] The numerical values, ranges, graphs, etc., exemplified in this embodiment are merely examples for explaining the present invention, and are not limited to these numerical values ​​and ranges. They can be appropriately optimized and implemented by those skilled in the art.

[0188] ○Furthermore, the present invention is not limited to this embodiment, and can be implemented by those skilled in the art by adding, deleting, or modifying as appropriate without departing from the scope of this disclosure. [Explanation of symbols]

[0189] θ…Ion concentration rate (=c s,avg / c s,max ) θ p ...Positive electrode ion concentration (=1-c) s,p,avg / c s,p,max ) D S [m 2 / s]... Solid-phase diffusion coefficient of lithium ions in the solid phase c[mol / m 3 ]... Lithium ion concentration of the active material c avg [mol / cm 3 ]...Average lithium ion concentration of the active material c s [mol / cm 3]...Lithium ion concentration on the surface of the active material c s,avg [mol / cm 3 ]...Average ion concentration on the surface of the active material R p ...Surface position in the particle diameter direction of the active material (solid phase particle size) j Li [mol / m 2 s]...Lithium ion flux c s,p,avg [mol / cm 3 ]...(Positive electrode) Solid-phase average lithium concentration c s,max [mol / cm 3 ]...Maximum ion concentration c s,p,max [mol / cm 3 ]...(Positive electrode) Maximum solid phase ion concentration CB (CB1, 2, 3)... Cellular battery CBS…Reference Cell Battery 10...Control device 11…Communication Interface (I / F) 12...Storage device 13...Arithmetic device 130...Measurement value acquisition unit 131...Positive electrode capacitance estimation unit 132...Battery deterioration degree estimation section 133...Positive electrode ion concentration estimation unit 134…Battery SOC estimation section 135...Battery SOC Control Unit 136... Abnormal cell detection unit

Claims

1. In a battery pack that combines multiple secondary battery cells, the control device is A step of estimating the ion concentration rate θ of the active material of any electrode plate of the cell battery, A cell cell plotting step in which one of the multiple cell cells is designated as a reference cell cell, and the ion concentration rates θ of the multiple cell cells estimated in the ion concentration rate θ estimation step are plotted on a common θ axis, A battery capacity correction step involves adjusting the length of other cell batteries according to their capacity, so that the length of the reference cell battery is equal to the length of the reference cell battery with a capacity of 1. The steps include: adjusting the position of the ion concentration rate θ on the θ axis so that the position of the ion concentration rate θ of other cell cells matches the position of the ion concentration rate θ of the reference cell cell on the θ axis; Steps for estimating the SOC of a battery pack include: estimating the SOC of a battery pack by setting the range between the ion concentration ratio θ at the lowest upper limit voltage and the ion concentration ratio θ at the highest lower limit voltage among the cell batteries to be 100 to 0% of the SOC of the battery pack; A method for controlling a battery pack, characterized by performing the following actions.

2. In the step of estimating the ion concentration ratio θ of the active material, A method for controlling a battery pack according to claim 1, characterized in that a solid-phase diffusion model of a secondary battery is used to calculate the solid-phase voltage difference of the positive electrode and the solid-phase voltage difference of the negative electrode in the thickness direction of the cell battery, the difference between the average ion concentration of the active material and the ion concentration on the surface of the active material is expressed using a first-order lag model, the ion concentration on the surface of the active material is derived from the average ion concentration of the active material and the volume-average ion concentration flux of the active material, and the ion concentration ratio θ is estimated from the average ion concentration on the surface of the active material and the maximum solid-phase ion concentration.

3. Prior to the step of estimating the ion concentration rate θ, A capacity estimation step of estimating the capacity of each electrode plate of the cell battery, A step of estimating the degree of degradation of the aforementioned cell battery, The battery pack control method according to claim 2, characterized by performing the following:

4. After the step of estimating the SOC of the battery pack, The battery pack control method according to claim 1, characterized in that it performs a simplified SOC estimation step of estimating SOC based solely on the ion concentration ratio θ of the aforementioned reference cell battery.

5. After the step of estimating the SOC of the battery pack, The battery pack control method according to claim 1, characterized in that it performs a step of determining an abnormal cell battery, in which, among the cell batteries, the SOC estimated based on the ion concentration ratio θ shows a large difference in the change of SOC compared to the other cell batteries.

6. Prior to the step of estimating the SOC of the battery pack, The battery pack control method according to claim 1, characterized by performing a cell battery voltage adjustment step of charging the cell battery with the lowest upper limit voltage among the cell batteries, or discharging the cell battery with the highest lower limit voltage.

7. In the capacity estimation step, which estimates the capacity of the electrode plates of each cell battery, The process of acquiring measured values ​​for the aforementioned cell battery generates an actual SOC voltage curve using the measurement results of the open-circuit voltage between 0% and 100% SOC, A theoretical value generation process that generates a theoretical SOC voltage curve calculated from the difference between a theoretical positive electrode open-circuit potential curve calculated from the content of at least one component of the positive electrode composite material of the cell battery using a fitting function and a theoretical negative electrode open-circuit potential curve calculated from the content of at least one component of the negative electrode composite material of the cell battery, An evaluation value calculation process that calculates the evaluation value using an evaluation function that calculates an evaluation value indicating the magnitude of the difference between the theoretical SOC voltage curve and the measured SOC voltage curve, A battery pack control method according to claim 3, characterized in that a computer performs the following analysis processing: repeatedly performing the theoretical value generation process and the evaluation value calculation process while changing a shift amount parameter that shifts the curve in the SOC direction with respect to at least one of the theoretical value curve of the positive electrode open circuit potential and the theoretical value curve of the negative electrode open circuit in the fitting function, and outputting the shift amount parameter that minimizes the evaluation value as the degree of degradation of the cell battery.

8. In the step of estimating the degree of degradation of the cell battery, A degradation estimation method for estimating the degradation of the aforementioned cell battery, Using the temperature of the aforementioned cell, the side reaction current generated at the negative electrode of the aforementioned cell is calculated. Based on the calculated side reaction current, the degradation index of the cell battery is calculated. A battery pack control method according to claim 3, characterized by using a degradation estimation method.

9. A method for controlling a battery pack according to any one of claims 1 to 8, characterized in that the electrode plate is a positive electrode plate.

10. A method for controlling a battery pack according to any one of claims 1 to 8, characterized in that the secondary battery is a lithium-ion secondary battery.

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