Battery state estimation device and battery state estimation method

Abstract

In the present invention, a battery capacity estimation device is provided with: a measurement unit 11 that measures the impedance (Z) of a secondary battery 1; and a battery state estimation unit 12 that estimates the state of the secondary battery 1. The battery state estimation unit 12 estimates, on the basis of the impedance (Z), at least one of an electric double layer capacity of the positive electrode and the reaction resistance of the positive electrode of the secondary battery 1, estimates, on the basis of the estimated electric double layer capacity, a structural change amount of a positive electrode active material by using the correlation between the electric double layer capacity and the structural change amount in which the structural change amount of the positive electrode active material increases as the electric double layer capacity is smaller or estimates, on the basis of the estimated reaction resistance, the structural change amount of the positive electrode active material by using the correlation between the reaction resistance and the structural change amount in which the structural change amount of the positive electrode active material increases as the reaction resistance is higher.

Description

Battery state estimation device and battery state estimation method

[0001] The present invention relates to a battery state estimation device and a battery state estimation method. This application claims priority based on the Japanese patent application No. 2024-209070, filed on November 29, 2024. In designated countries where incorporation by reference is permitted, the contents described in the above application are incorporated into this application by reference and constitute part of the description of this application.

[0002] A conventional method for determining cracks in the positive electrode active material of a secondary battery involves acquiring pair data, which consists of the square root of the cumulative discharge amount from when the battery was new to that point, and the battery capacity at that point, multiple times. The linear coefficient of determination is calculated when these pair data are approximated by a linear function. Only if the acquired linear coefficient of determination is smaller than a predetermined tolerance value that allows the battery to be used as is, the quadratic coefficient of determination is calculated when these pair data are approximated by a quadratic function. If the quadratic coefficient of determination is greater than or equal to a threshold, it is determined that cracks have occurred in the positive electrode active material (as described in Patent Document 1).

[0003] Japanese Patent Publication No. 2011-228213

[0004] The determination method described in Patent Document 1 can determine whether or not cracks have occurred in the positive electrode active material, but it has the problem that it cannot estimate the amount of structural change in the positive electrode active material.

[0005] The problem that this invention aims to solve is to provide a battery state estimation device and a battery state estimation method that can estimate the amount of structural change of the positive electrode active material.

[0006] This invention relates to the electrical double layer capacitance (C) based on the impedance (Z) of the secondary battery 1. ｄｌ ) or reaction resistance (R ｃｔ Estimate at least one of the following: the electrical double layer capacitance (C ｄｌ Using the correlation between electrical double layer capacitance and structural change, where a smaller value of ) results in a larger amount of cracks, the estimated electrical double layer capacitance (C) ｄｌ The amount of structural change is estimated based on ) or the reaction resistance (R ｃｔThe larger the value of (), the greater the amount of structural change. Using the correlation between reaction resistance and the amount of structural change, the estimated reaction resistance (R ｃｔ Based on), the amount of structural change is estimated to solve the above problems.

[0007] According to the present invention, the amount of structural change of the positive electrode active material can be estimated.

[0008] FIG. 1 is a block diagram showing a battery state estimation system according to the present embodiment. FIG. 2 is a graph showing the correlation between the number of charge-discharge cycles of a secondary battery and the electric double layer capacitance (C ｄｌ ). FIG. 3 is a graph showing the correlation between the number of charge-discharge cycles of a secondary battery and the reaction resistance (R ｃｔ ). FIG. 4 is a graph showing the correlation between the electric double layer capacitance (C ｄｌ ) of a secondary battery and the amount of cracks. FIG. 5 is a graph showing the correlation between the reaction resistance (R ｃｔ ) of a secondary battery and the amount of cracks. FIG. 6 is a graph showing the characteristics of the electric double layer capacitance (C ｄｌ ) with respect to the integrated charge-discharge current amount (Q). FIG. 7 is a graph showing the characteristics of the electric double layer capacitance (C ｄｌ ) with respect to the integrated charge-discharge current amount (Q). FIG. 8 is a graph showing the correlation between the electric double layer capacitance (C ｄｌ ) of a secondary battery and the reaction resistance (R ｃｔ ). FIG. 9 is a circuit diagram showing an equivalent circuit of the electrolyte and the positive electrode included in the secondary battery. FIG. 10 is a graph for explaining a method of calculating equivalent circuit parameters. FIG. 11 is a flowchart showing the procedure of the battery state estimation method by the battery state estimation system according to the present embodiment. FIG. 12 is a graph showing the correlation between the electric double layer capacitance (C ｄｌ ) of a secondary battery and the amount of crystal structure change. FIG. 13 is a graph showing the correlation between the reaction resistance (R ｃｔ ) of a secondary battery and the amount of crystal structure change.

[0009] <First Embodiment> The battery state estimation system according to this embodiment will be described based on the drawings. Figure 1 is a block diagram showing the battery state estimation system according to this embodiment. The battery state estimation system measures the impedance of a secondary battery, estimates at least one of the positive electrode's electric double layer capacitance or the positive electrode's reaction resistance, and uses the correlation between the positive electrode's electric double layer capacitance and the amount of structural change of the positive electrode active material, or the correlation between the positive electrode's reaction resistance and the amount of structural change of the positive electrode active material, to estimate the amount of structural change of the positive electrode active material based on the estimated electric double layer capacitance or reaction resistance. Note that the device equipped with the controller 10 corresponds to the "battery state estimation device" of the present invention, and the method executed by the controller 10 corresponds to the "battery state estimation method" of the present invention. Furthermore, in the following description, "positive electrode's electric double layer capacitance," "positive electrode's reaction resistance," "amount of structural change of positive electrode active material," "amount of cracks in positive electrode active material," and "amount of crystal structure change of positive electrode active material" will be referred to as "electric double layer capacitance," "reaction resistance," "amount of structural change," "amount of cracks," and "amount of crystal structure change," respectively.

[0010] As shown in Figure 1, the battery state estimation system comprises a secondary battery 1, a DC-DC converter 2, a voltage sensor 3, a current sensor 4, an impedance meter 5, and a controller 10. The secondary battery 1 includes a group of batteries connected together. The secondary battery 1 is, for example, a lithium-ion secondary battery. While not particularly limited, examples of lithium-ion secondary batteries include those using silicon or a silicon-containing active material as the negative electrode active material, or those using a sulfur-containing active material as the positive electrode active material. Furthermore, the secondary battery 1 may be an electrolyte lithium-ion secondary battery or an all-solid-state lithium-ion secondary battery.

[0011] The positive electrode of the battery included in secondary battery 1 is electrically connected to the negative electrode of another battery via a busbar, although this is not shown in the diagram. In other words, the multiple batteries included in secondary battery 1 are modularized by being connected via a busbar.

[0012] The DC-DC converter 2 is a power conversion device that converts the voltage input from the secondary battery 1 to a predetermined voltage and outputs power to a load such as a motor. The DC-DC converter 2 also converts the voltage input from a load such as a motor or a charging device to a predetermined voltage and outputs power to the secondary battery 1. This DC-DC converter 2 is controlled by the controller 10. The secondary battery 1 is connected to the input side of the DC-DC converter 2, and the load is connected to the output side of the DC-DC converter 2. The load is a charging device, and the secondary battery 1 is electrically connected to the charging device.

[0013] The voltage sensor 3 is a sensor for detecting the voltage between the terminals of the secondary battery 1. The voltage sensor 3 is connected between the wiring connected to the positive and negative terminals of the secondary battery 1. The current sensor 4 is a sensor for detecting the input and output current of the secondary battery 1. The current sensor 4 is connected to the wiring connected to either the positive or negative terminal of the secondary battery 1. The voltage sensor 3 and the current sensor 4 detect the state of the battery and output the detected values ​​to the controller 10.

[0014] The impedance meter 5 is connected to the secondary battery 1 and measures the AC impedance (complex impedance) of the secondary battery 1 by receiving an AC perturbation current as an input signal and obtaining a response voltage corresponding to the AC signal (AC current). The impedance meter 5 can be arbitrarily selected from those commonly used as general AC impedance measuring devices. For example, the impedance meter 5 may measure the AC impedance of the secondary battery 1 by changing the frequency of the AC perturbation current over time using the AC impedance method. The method of measuring AC impedance in the AC impedance method is not particularly limited. For example, analog methods such as the Lissajous method and the AC bridge method, or digital methods such as the digital Fourier integral method and the fast Fourier transform method with noise application can be appropriately employed. In this embodiment, multiple AC perturbation currents with different frequencies are applied to the secondary battery 1 and the AC impedance is measured. The multiple frequencies are, for example, the real part Z that constitutes the AC impedance Z measured by the impedance meter 5. ｒｅ and the imaginary component Zｉｍ The reaction resistance component of the secondary battery 1 can be calculated from a graph (Nyquist plot; Cole-Cole plot) plotted on a complex plane coordinate system, as long as it is within that range. There are no particular restrictions on the amplitude of the waveform (e.g., sine wave) of the AC perturbation current applied to the battery, and it can be set arbitrarily. The measurement result of the AC impedance measured by the impedance meter 5 is sent to the controller 10 as the output of the impedance meter 5. In the following explanation, the AC impedance measured by the impedance meter 5 will also be simply referred to as impedance (Z).

[0015] The controller 10 is a battery control unit (BCU). Based on the detected voltage detected by the voltage sensor 3 and / or the detected current detected by the current sensor 4, the controller 10 controls the charging and discharging of the secondary battery 1 and estimates the battery capacity of the secondary battery 1. The controller 10 is composed of memory such as ROM or RAM, and a processor such as a CPU. The controller 10 also has a measurement unit 11 and a battery state estimation unit 12 as functional blocks for performing functions such as measuring the impedance (Z) of the secondary battery 1, controlling the charging and discharging of the secondary battery 1, and estimating the state of the secondary battery 1. Note that the controller 10 may have other functional blocks besides the measurement unit 11, and the functional blocks included in the controller 10 are not limited to the two shown in Figure 1.

[0016] The measurement unit 11 controls the impedance meter 5 to measure the impedance (Z) of the secondary battery 1. The measurement unit 11 sets a measurement frequency for obtaining positive electrode information and outputs the set frequency value to the impedance meter 5. As will be described later, in order to estimate the state of the positive electrode of the secondary battery 1 from the impedance (Z), it is necessary to obtain the positive electrode information from the impedance (Z) while distinguishing it from information from other parts such as the electrolyte and the negative electrode. The frequency band suitable for extracting positive electrode information is predetermined by the battery materials and structure contained in the secondary battery 1. Therefore, in order to distinguish the information, the frequency used when measuring the impedance (Z) should be set within the frequency band suitable for extracting positive electrode information. In this embodiment, a frequency band that is less affected by the negative electrode and Warburg impedance can be set, thereby improving the accuracy of estimating the positive electrode state. The impedance meter 5 applies an AC perturbation current with the measurement frequency set by the measurement unit 11 to the secondary battery 1 to measure the impedance (Z) and outputs the measured value to the measurement unit 11. In the following explanation, charging and discharging will be collectively referred to as "charge and discharge," but charging and discharge only requires performing at least one of either charging or discharging.

[0017] The battery state estimation unit 12 estimates the state of the secondary battery 1 based on the impedance (Z) measured by the measurement unit 11 at multiple measurement frequencies. Specifically, the battery state estimation unit 12 estimates at least one of the electric double layer capacitance or the reaction resistance based on the impedance (Z) measured by the measurement unit 11. The battery state estimation unit 12 estimates the amount of structural change based on the estimated electric double layer capacitance, using a correlation where the amount of structural change increases as the electric double layer capacitance decreases (hereinafter also referred to as the "correlation between electric double layer capacitance and amount of structural change"). The battery state estimation unit 12 also estimates the amount of structural change based on the estimated reaction resistance, using a correlation where the amount of structural change increases as the reaction resistance increases (hereinafter also referred to as the "correlation between reaction resistance and amount of structural change"). When the battery state estimation unit 12 estimates the electric double layer capacitance, it is sufficient to estimate the amount of structural change using the correlation between electric double layer capacitance and amount of structural change. When the battery state estimation unit 12 estimates the electric double layer capacitance, it is sufficient to estimate the amount of structural change using the correlation between reaction resistance and amount of structural change.

[0018] This section describes the degradation of the positive electrode active material of secondary battery 1 due to crack formation and changes in crystal structure (crystal structure change). Degradation of the positive electrode occurs due to factors such as changes in crystal structure, film formation, and crack formation. For example, when considering the recycling of secondary battery 1, it is desirable to understand which factor is causing the degradation of the positive electrode. When the positive electrode active material degrades due to crack formation or changes in crystal structure, it is advisable to estimate the amount of structural change in order to understand the degree of degradation. The amount of structural change represents the degree of degradation when the positive electrode active material degrades due to crack formation or changes in crystal structure. Structural changes in the positive electrode active material include external changes and internal changes of the active material. Crack formation corresponds to a change in the external shape of the active material (visual change), and internal changes correspond to changes in crystal structure. In this invention, among the amounts of structural change, the amount of cracks is estimated as an indicator representing external changes, and the amount of crystal structure change is estimated as an indicator representing internal changes. In this embodiment, the objective is to estimate the amount of cracks as an indicator showing the degree of degradation when the positive electrode active material degrades due to crack formation.

[0019] When a crack occurs in the positive electrode of secondary battery 1, the positive electrode active material breaks, increasing the distance lithium travels and resulting in an electrically isolated state. The degradation of secondary battery 1 progresses with repeated charge-discharge cycles, but according to the inventor's knowledge, the mechanism of positive electrode degradation differs depending on the number of cycles.

[0020] For example, if cracks occur in the early stages of degradation, the cracked portion of the positive electrode active material will break, increasing the surface area, which in turn increases the electrical double layer capacitance and decreases the reaction resistance. Also, in the early stages of degradation, the increase in surface area due to cracks is stronger than the decrease in active surface area due to changes in crystal structure, so overall, the electrical double layer capacitance tends to increase and the reaction resistance tends to decrease. Furthermore, as the degradation of the positive electrode progresses beyond the early stages, cracking of the positive electrode active material continues, but since the cracked portion has already broken in the early stages of degradation, the rate of increase in electrical double layer capacitance due to cracks slows down compared to the early stages. Also, as the cracking of the positive electrode active material progresses, more positive electrode active material becomes isolated, and the decrease in active surface area due to changes in crystal structure also progresses, so overall, the electrical double layer capacitance tends to decrease and the reaction resistance tends to increase. In other words, the main factors affecting positive electrode degradation differ between the early stages of degradation and the later stages of degradation, so the electrical double layer capacitance and reaction resistance change with different characteristics depending on the type and degree of degradation.

[0021] Figure 2 shows the number of charge / discharge cycles and the electric double layer capacity (C) of secondary battery 1. ｄｌ Figure 2 is a graph showing the correlation between the number of cycles and the electric double layer capacitance (C) from experimental data of secondary battery 1. ｄｌ This is a line graph plotting the data for the following stages: Ta represents the early stages of degradation when degradation has not yet progressed, and Tb represents the later stages of degradation when degradation has progressed. In the early stages of degradation (Ta), the electrical double-layer capacitance increases as the number of cycles increases. In the later stages of degradation, the electrical double-layer capacitance decreases as the number of cycles increases.

[0022] Figure 3 shows the number of charge / discharge cycles and the reaction resistance (R) of secondary battery 1. ｃｔ Figure 3 is a graph showing the correlation between the number of cycles and the reaction resistance (R) from experimental data of secondary battery 1. ｃｔThis is a line graph plotting the data for the following stages: Ta represents the early stages of degradation when degradation has not yet progressed, and Tb represents the stages after the early stages of degradation when degradation has progressed. In the early stages of degradation (Ta), the reaction resistance decreases as the number of cycles increases. After the early stages of degradation, the reaction resistance increases as the number of cycles increases. In the early stages of degradation, cracks are minor, and in order to estimate the amount of cracks in the later stages of degradation, in this embodiment, the correlation between electrical double layer capacitance and crack amount, or the correlation between reaction resistance and crack amount, is used to estimate the amount of cracks. Note that the correlation between electrical double layer capacitance and crack amount shows that the amount of cracks increases as the electrical double layer capacitance decreases, and the correlation between reaction resistance and crack amount shows that the amount of cracks increases as the reaction resistance increases.

[0023] Next, the correlation between electrical double layer capacitance and crack amount, and the correlation between reaction resistance and crack amount will be explained with reference to Figures 4 and 5. Figure 4 shows the electrical double layer capacitance (C) of secondary battery 1. ｄｌ Figure 4 is a graph showing the correlation between the electric double layer capacitance (C) and the amount of cracks. From the experimental data of secondary battery 1, the electric double layer capacitance (C) ｄｌ Figure 4 shows a graph plotting the data between the electrical double layer capacitance and the amount of cracks, and an approximate curve being drawn. As shown in Figure 4, the amount of cracks increases as the electrical double layer capacitance decreases. Figure 5 shows the reaction resistance (R) of secondary battery 1. ｃｔ Figure 5 is a graph showing the correlation between the reaction resistance (R) and the amount of cracks from experimental data of secondary battery 1. ｃｔ This graph plots the reaction resistance against the amount of cracking and shows an approximate curve. As shown in Figure 5, the greater the reaction resistance, the greater the amount of cracking.

[0024] The battery state estimation unit 12 stores in memory a map showing the correlation between electric double layer capacitance and crack amount, or a map showing the correlation between reaction resistance and crack amount. By referring to the map, it estimates the value corresponding to the estimated electric double layer capacitance as the crack amount, or estimates the value corresponding to the estimated reaction resistance as the crack amount. For example, if the electric double layer capacitance estimated based on impedance (Z) is C ｄｌ＿ａIn this case, the battery state estimation unit 12 determines the electric double layer capacitance (C) from the graph showing the correlation between electric double layer capacitance and crack amount (corresponding to the dotted line graph in Figure 4). ｄｌ＿ａ Crack amount (Cr) corresponding to ) ＿ａ We estimate the following.

[0025] The battery state estimation unit 12 determines whether the current state of the secondary battery 1 is in the early stages of degradation or beyond. Figure 6 shows the electric double layer capacity (C) in relation to the integrated charge / discharge current (Q). ｄｌ This graph shows the characteristics of the device. Figure 6 shows the characteristics in the early stages of degradation. ΔQ is the interval of the integrated charge and discharge current used to determine whether the electrical double-layer capacitance is increasing or decreasing. If ΔQ is too small, the degradation state will hardly change in a short period, and there is a possibility of misjudgment due to variations such as measurement errors. Also, if ΔQ is too long, the number of measurement data points required to identify the increasing or decreasing trend of the electrical double-layer capacitance will be large. Therefore, ΔQ should be set based on actual durability test data so that the increasing or decreasing trend of the electrical double-layer capacitance can be identified without requiring too many measurement data points. The integrated value of the charge and discharge current (Q) corresponds to the number of cycles.

[0026] The battery state estimation unit 12 acquires the detected value from the current sensor 4 and calculates the integrated value (Q) of the charge and discharge current of the secondary battery 1. The battery state estimation unit 12 also calculates the electric double layer capacitance (C) based on the impedance (Z) measured by the measurement unit 11. ｄｌ The battery state estimation unit 12 calculates the integrated value of the charge and discharge current (Q) and the electric double layer capacitance (C). ｄｌ The estimation of the electrical double layer capacitance (C) is repeatedly performed, and the integrated value (Q) and the electrical double layer capacitance (C) are obtained. ｄｌ Obtain multiple measurement data including ).

[0027] The battery state estimation unit 12 then calculates the electric double layer capacitance (C) between two measurement data points separated by ΔQ. ｄｌ The system determines whether the electric double layer capacitance (C) is increasing or decreasing. The circles in Figure 6 represent the measurement data. For example, the battery state estimation unit 12 plots the measurement data within ΔQ and calculates an approximate straight line, and from the slope of the approximate straight line, it determines the electric double layer capacitance (C) ｄｌThe unit determines whether the electric double layer capacitance (C) is increasing or decreasing. In the example in Figure 6, since the slope of the approximate line is positive, the battery state estimation unit 12 determines that the electric double layer capacitance (C) is increasing or decreasing. ｄｌ The battery state estimation unit 12 determines that the electric double layer capacity (C) is on an increasing trend. The battery state estimation unit 12 determines that the current state of the secondary battery 1 is in the early stages of deterioration by determining that the electric double layer capacity is on an increasing trend. In addition, if the slope of the approximate straight line is negative, the battery state estimation unit 12 determines that the electric double layer capacity (C) is on an increasing trend. ｄｌ It can be determined that the value is on a downward trend, and that the current state of secondary battery 1 is beyond the initial stage of degradation.

[0028] The battery state estimation unit 12 determines the reaction resistance (R ｃｔ The battery state estimation unit 12 calculates the integrated value of the charge and discharge current (Q) and the reaction resistance (R ｃｔ The estimation of the integrated value (Q) and the reaction resistance (R) is repeatedly performed, and the integrated value (Q) and the reaction resistance (R) are obtained. ｃｔ Multiple measurement data including ) are obtained. The battery state estimation unit 12 determines the reaction resistance (R) between two measurement data points separated by ΔQ. ｃｔ The battery state estimation unit 12 determines whether the electric double layer capacitance (C) is on a downward or upward trend. ｄｌ Similar to the above determination method based on ), the measurement data within ΔQ is plotted to calculate an approximate straight line, and the reaction resistance (R) is determined from the slope of the approximate straight line. ｃｔ The battery state estimation unit 12 determines whether the reaction resistance (R) is decreasing or increasing. If the slope of the approximate straight line is negative, the unit determines whether the reaction resistance (R) is decreasing or increasing. ｃｔ The battery state estimation unit 12 determines that the reaction resistance (R) is on a downward trend, and that the current state of secondary battery 1 is in the early stages of deterioration. Furthermore, if the slope of the approximate straight line is positive, the battery state estimation unit 12 determines that the reaction resistance (R) is in the early stages of deterioration. ｃｔ By determining that the value is increasing, it can be determined that the current state of secondary battery 1 is beyond the initial stage of degradation.

[0029] Furthermore, the battery state estimation unit 12 determines the electric double layer capacitance (C ｄｌ The above determination method based on ) and the reaction resistance (R ｃｔ By combining the above determination method based on ), the electrical double layer capacitance (C ｄｌ) is on a downward trend, and the reaction resistance (R ｃｔ The battery state estimation unit 12 may determine that the current state of the secondary battery 1 is beyond the initial stage of degradation by determining that the electric double layer capacity (C) is on an increasing trend. ｄｌ ) and / or reaction resistance (R ｃｔ The amount of cracking is estimated based on the electrical double layer capacitance (C). ｄｌ ) and reaction resistance (R ｃｔ When estimating the amount of cracks based on ), the electrical double layer capacitance (C) ｄｌ Crack amount and reaction resistance (R) based on ) ｃｔ If the estimated crack amount based on ) results in different values, the battery state estimation unit 12 may, for example, estimate the average value as the final crack amount. In this way, when the battery state estimation unit 12 determines that the electric double layer capacity is decreasing or the reaction resistance is increasing, or at least one of the two trends, it estimates the crack amount based on the correlation between electric double layer capacity and crack amount, or the correlation between reaction resistance and crack amount.

[0030] The battery state estimation unit 12 may also determine whether the current state of the secondary battery 1 is in the early stages of degradation or beyond, based on the integrated value of the charge and discharge currents of the secondary battery 1. From the actual durability test data of the secondary battery 1, a correlation relationship like that shown in Figure 2 or Figure 3 can be obtained, and the electric double layer capacity (C) can be determined. ｄｌ The cumulative value of the charge / discharge current or the number of cycles when the reaction resistance (R) changes from an increasing trend to a decreasing trend can be determined in advance. Similarly, from the actual durability test data of secondary battery 1, the reaction resistance (R) can be determined in advance. ｃｔ The battery state estimation unit 12 can pre-determine the integrated value of the charge / discharge current or the number of cycles when the electric double layer capacity (C) changes from a decreasing trend to an increasing trend. ｄｌ When the reaction resistance (R) changes from an increasing trend to a decreasing trend, or when the reaction resistance (R) changes ｃｔ A threshold value for the cumulative charge and discharge current (cumulative threshold) is set in advance to correspond to the time when the cumulative charge and discharge current changes from a decreasing trend to an increasing trend. The battery state estimation unit 12 may then determine that the battery has deteriorated beyond the initial stage if the cumulative charge and discharge current is equal to or greater than the predetermined cumulative threshold.

[0031] The battery state estimation unit 12 estimates the electric double layer capacitance (C) based on the impedance (Z). ｄｌ ) or reaction resistance (R ｃｔ If the estimated value of ) shows an abnormal value due to noise, etc., then the electrical double layer capacitance (C) ｄｌ ) or reaction resistance (R ｃｔ The estimated values ​​of ) can be excluded as outliers and do not need to be used in estimating the amount of cracking. The method for excluding outliers is explained below.

[0032] Figure 7 shows the relationship between the integrated charge / discharge current (Q) and the electric double layer capacitance (C). ｄｌ This is a graph showing the characteristics of the battery. Figure 7 shows the characteristics from the early stages of degradation onward. The battery state estimation unit 12 calculates the current predicted value of the electric double layer capacity (C) based on the history of the estimated electric double layer capacity. ｄｌ＿ｐ The battery state estimation unit 12 predicts the electric double layer capacitance (C) based on the impedance (Z) measured by the measurement unit 11. ｄｌ The battery state estimation unit 12 estimates the electric double layer capacitance (C) that has been estimated so far at predetermined intervals. ｄｌ The battery state estimation unit 12 stores the integrated charge / discharge current value or the number of cycles at the time of estimation in its internal memory. The circles in Figure 7 represent measurement data (past data). The battery state estimation unit 12 calculates an approximate curve from the past data of the integrated charge / discharge current value and the estimated electric double layer capacity stored in the internal memory. In the example in Figure 7, the battery state estimation unit 12 calculates an approximate curve (Pw) from the past data in ΔQ. The battery state estimation unit 12 sets the value corresponding to the current integrated charge / discharge current value on the extension of the approximate curve (Pw) to the electric double layer capacity (C). ｄｌ Current predicted value (C) ｄｌ＿ｐ ) predicts point C in Figure 7. ｄｌ＿ｐ The current electric double layer capacitance (C) predicted from the approximation curve (Pw) ｄｌ ) Furthermore, the battery state estimation unit 12 calculates the electric double layer capacitance (C) based on the impedance (Z) measured by the measurement unit 11. ｄｌ ) Current value (Current estimated value: C ｄｌ＿ｅ The battery state estimation unit estimates the current estimated value (C). ｄｌ＿ｅ ) and current predicted value (C ｄｌ＿ｐ The difference between this value and a predetermined difference threshold (ΔC) is calculated, and the difference is found to be equal to the difference threshold (ΔC). ｄｌDetermine whether it is greater than (). The difference threshold (ΔC ｄｌ ) is a threshold for determining whether the current estimated value (C ｄｌ＿ｅ ) is an abnormal value, and corresponds to the allowable deviation amount with respect to the current predicted value (C ｄｌ＿ｐ ).

[0033] In the example of FIG. 7, the current estimated value (C ｄｌ＿ｅ ) is affected by noise or the like and deviates from a predetermined width (±ΔC ｄｌ＿ｐ ) centered on the current predicted value (C ｄｌ ). The difference between the current estimated value (C ｄｌ＿ｅ ) and the current predicted value (C ｄｌ＿ｐ ) is greater than the difference threshold (ΔC ｄｌ ), so the battery state estimation unit 12 sets the current estimated value (C ｄｌ＿ｅ ) as an abnormal value. Then, the battery state estimation unit 12 does not use the current estimated value (C ｄｌ＿ｅ ) which is an abnormal value for estimating the crack amount. That is, when the difference between the current estimated value (C ｄｌ＿ｅ ) and the current predicted value (C ｄｌ＿ｐ ) is greater than a predetermined difference threshold (ΔC ｄｌ ), the battery state estimation unit 12 does not use the current estimated value (C ｄｌ＿ｅ ) for estimating the crack amount, and when the difference between the current estimated value (C ｄｌ＿ｅ ) and the current predicted value (C ｄｌ＿ｐ ) is less than or equal to the difference threshold (ΔC ｄｌ ), the battery state estimation unit 12 uses the current estimated value (C ｄｌ＿ｅ ) for estimating the crack amount.

[0034] The battery state estimation unit 12 may also not use the estimated value of the reaction resistance (R ｃｔ ) for estimating the crack amount when the estimated value of the reaction resistance (R ｄｌ ) shows an abnormal value, similar to the above electric double layer capacitance (C ｃｔ ). The method for excluding abnormal values of the reaction resistance (R ｃｔ ) is the same as the method for excluding abnormal values of the above electric double layer capacitance (C ｃｔ ). Among the methods for excluding abnormal values of the above electric double layer capacitance (C ｄｌ ), the current predicted value (C ｄｌ ), the current estimated value (C ｄｌ＿ｐ )ｄｌ＿ｅ ), and the differential threshold (ΔC ｄｌ ) are each the reaction resistance (R ｃｔ Current predicted value (R ｃｔ＿ｐ ), current estimate (R ｃｔ＿ｅ ), and the difference threshold (ΔR ｃｔ ) can be replaced accordingly. Then, the battery state estimation unit 12 will determine the reaction resistance (R ｃｔ Based on the history of estimated values ​​of ), the reaction resistance (R ｃｔ Current predicted value (R ｃｔ＿ｐ ) predicts the response resistance (R) based on the impedance (Z). ｃｔ Current estimate of (R ｃｔ＿ｅ ) is estimated. Current estimate (R ｃｔ＿ｅ ) and the current predicted value (R ｃｔ＿ｐ The difference from ) is a predetermined difference threshold (ΔR ｃｔ If it is greater than the current estimated value (R ｃｔ＿ｅ ) is not used to estimate the amount of cracks, and the current estimated value (R ｃｔ＿ｅ ) and the current predicted value (R ｃｔ＿ｐ The difference with the difference threshold (ΔR ｃｔ If the current estimated value (R) is less than or equal to the current estimated value, the battery state estimation unit 12 will determine the current estimated value (R) ｃｔ＿ｅ This is used to estimate the amount of cracking.

[0035] In this embodiment, the battery state estimation unit 12 may exclude abnormal values ​​using the method described below. Figure 8 shows the electric double layer capacity (C) of the secondary battery 1. ｄｌ ) and reaction resistance (R ｃｔ Figure 8 is a graph showing the correlation with the electric double layer capacitance (C) as the integrated value of the charge / discharge current or the number of cycles is varied from experimental data. ｄｌ ) and reaction resistance (R ｃｔ ) and calculate the electrical double layer capacitance (C ｄｌ ) and reaction resistance (R ｃｔ This is a scatter plot of the data from ). Also, two graphs CR а and CR ｂ The area enclosed by the box is the electrical double layer capacitance (C ｄｌ ) and reaction resistance (R ｃｔ ) is the range that can be taken. And the range (CR а CR ｂElectrical double layer capacitance (C) outside of ) ｄｌ ) and reaction resistance (R ｃｔ The combination of ) is judged as an outlier. Note that the range (CR а CR ｂ The value of the secondary battery 1 is determined experimentally, depending on the materials and structure of the secondary battery 1.

[0036] The battery state estimation unit 12 estimates the electric double layer capacitance and reaction resistance based on the impedance (Z) measured by the measurement unit 11. ｄｌ ) Estimated value and reaction resistance (R ｃｔ The system determines whether the combination of estimated values ​​of ) is outside or inside a predetermined region. The predetermined region is set on a map showing the correspondence between electric double layer capacitance and reaction resistance, and is within the range shown in Figure 8 (CR а CR ｂ ) corresponds to the electric double layer capacitance (C ｄｌ ) Estimated value and reaction resistance (R ｃｔ If the combination of estimated values ​​of ) falls outside the predetermined range, then the electrical double layer capacitance (C) ｄｌ ) Estimated value and reaction resistance (R ｃｔ The estimated value of ) is not used to estimate the amount of cracking, and the electrical double layer capacitance (C) is not used. ｄｌ ) Estimated value and reaction resistance (R ｃｔ If the combination of estimated values ​​of ) falls within a predetermined range, then the electrical double layer capacitance (C) ｄｌ ) Estimated value and reaction resistance (R ｃｔ The estimated value of ) is used to estimate the amount of cracking.

[0037] The battery state estimation unit 12 calculates the electric double layer capacitance (C) based on the impedance (Z) measured at multiple measurement frequencies. ｄｌ ) and reaction resistance (R ｃｔ ) is estimated. Figure 9 is a circuit diagram showing the equivalent circuit of the electrolyte and positive electrode contained in secondary battery 1. R ｏR represents the electrolyte resistance, R represents the positive electrode reaction resistance, and C represents the positive electrode's electric double layer capacitance. The equivalent circuit of secondary battery 1 also includes the negative electrode's RC parallel circuit, but depending on the frequency band of the AC current flowing through secondary battery 1, the impedance of the negative electrode's electric double layer capacitance can be made so small that it is negligible compared to the impedance of the positive electrode. The equivalent circuit shown in Figure 9 corresponds to the equivalent circuit when a current in a frequency band that makes the negative electrode's RC parallel circuit practically negligible is flowed through it.

[0038] Equivalent impedance (Z) in the equivalent circuit ｃｅｌｌ The expression is given by the following equation (1). Note that ω is the angular frequency determined by the frequency of the AC signal.

[0039] From equation (1), the imaginary part (Z ｉｍ If we extract only the part shown, we derive equation (2) below.

[0040] Further transformation of equation (2) yields equation (3) below.

[0041] In equation (3), -1 / (ωZ) ｉｍ ) with y on the vertical axis, 1 / ω ２ If we plot the horizontal axis (x) and draw a graph, we get the graph shown in Figure 10. From the graph, the slope (m = 1 / (CR) ２ By reading the response resistance (R) and intercept (C), the reaction resistance (R) and electric double layer capacitance (C) of the positive electrode can be estimated. That is, the graph shown in Figure 10 is represented by a straight line equation, and the imaginary impedance (Z) of the two points ｉｍ If the following is obtained, the characteristics of a straight line can be derived. For this reason, the measurement unit 11 measures impedance at at least two measurement frequencies. The battery state estimation unit 12 then uses the measured impedance values ​​measured by the measurement unit 11 to derive characteristics corresponding to the graph in Figure 7 by linear regression calculation, and the slope of the line (m = 1 / (CR) ２ By determining the )) and the intercept (C), the reaction resistance (R) and electric double layer capacitance (C) of the positive electrode can be estimated as the positive electrode state of secondary battery 1. Then, the electric double layer capacitance (C) and reaction resistance (R) of the positive electrode calculated in the above calculation are used to estimate the electric double layer capacitance (C) ｄｌ ) Estimated value and reaction resistance (Rｃｔ These correspond to the estimated values ​​of ).

[0042] Next, the control flow of the battery state estimation method in this embodiment will be described. Figure 11 is a flowchart showing the procedure of the battery state estimation method by the battery state estimation system according to this embodiment. Note that the flowchart shown in Figure 11 is executed repeatedly at a predetermined period. In the following description of the flowchart, ΔT represents the calculation period, and Q represents the variable for the time interval count. The initial state of Q is zero.

[0043] The controller 10 manages an estimated state variable (S) as a value indicating the control state for estimating the battery state, and sets the estimated state variable (S) in accordance with the progression of the control sequence. The initial value of the estimated state variable (S) is zero, it increases as the sequence progresses, and is reset when the estimation of the battery state is complete.

[0044] In step S1, the battery state estimation unit 12 integrates the charge and discharge currents and calculates an integrated value (Q). Specifically, it calculates the current integrated value by adding the value obtained by multiplying the charge and discharge current value by the calculation period (ΔT) to the previous integrated value. In step S2, the controller 10 determines whether no current is flowing through the secondary battery 1 (current = 0) and whether the relaxation time has elapsed. When measuring the impedance (Z) of the secondary battery 1, the battery state continues to change while current is flowing or for a while after current has flowed. Therefore, the determination flow in step S2 is provided to avoid the battery state changing during impedance measurement. If current is flowing through the secondary battery 1 (current ≠ 0), or if the current is zero but the relaxation time has not elapsed, the determination flow in step S2 becomes "No", and the controller 10 terminates the control flow shown in Figure 11.

[0045] If no current is flowing through the secondary battery 1 (current = 0) and the relaxation time has elapsed, in step S3, the measurement unit 11 measures the impedance (Z). Based on the impedance (Z), the battery state estimation unit 12 calculates the electric double layer capacitance (C). ｄｌ [x]) and reaction resistance (R ｃｔEstimate [x]), where x represents the number of loop iterations, and C ｄｌ [x] and R ｃｔ [x] is the electric double layer capacitance (C) estimated in the control flow of step S3 in the xth loop. ｄｌ ) and reaction resistance (R ｃｔ This represents the value of ). Furthermore, when the battery state estimation unit 12 calculates the integrated current value (Q) after the xth loop, it performs calculations for Q[0] to Q[x] and counts the number of values ​​m that are smaller than Q - ΔQ within Q[0] to Q[x]. Then, the integrated current value Q[x] and the electric double layer capacitance C calculated or estimated in the xth loop are used. ｄｌ [x] and reaction resistance R ｃｔ [x] is Q[x-m], and the electrical double layer capacitance C is C. ｄｌ [x-m], reaction resistance R ｃｔ Replace with [x-m]. Also, the integrated current value Q[x-1] and the electrical double layer capacitance C. ｄｌ [x-1] and reaction resistance R ｃｔ Let [x-1] be Q[x-1-m], and the electrical double layer capacitance C ｄｌ [x-1-m], reaction resistance R ｃｔ Replace it with [x-1-m]. Then, replace it sequentially until you get the integrated current value Q [m] and the electrical double layer capacitance C. ｄｌ [m], reaction resistance R ｃｔ Replace it with [m]. Also, replace the loop count x with x-m. In other words, the controller 10 repeatedly executes the loop process, securing measurement data corresponding to ΔQ from the current point in time, and discarding measurement data older than the measurement data corresponding to ΔQ. That is, m past data points are excluded from processing.

[0046] In step S4, the battery state estimation unit 12 determines the reaction resistance R ｃｔ [x] and electrical double layer capacitance C ｄｌ Determine whether the combination of [x] falls within a predetermined range. Reaction resistance R ｃｔ [x] and electrical double layer capacitance C ｄｌ If it is determined that the combination of [x] is outside the predetermined range, in step S5 the battery state estimation unit 12 determines the reaction resistance R ｃｔ [x] and electrical double layer capacitance C ｄｌThe combination of [x] is determined to be an outlier, and the loop count [x] is reset to x-1 (step S5). This ensures that if the current measurement data is an outlier, the current measurement data is discarded.

[0047] Reaction resistance R ｃｔ [x] and electrical double layer capacitance C ｄｌ If the controller determines that the combination of [x] is within a predetermined range, in step S6 the controller determines whether the estimated state variable (S) is zero. If the estimated state variable (S) is zero, in step S7 the controller determines whether the integrated current value (Q) is greater than ΔQ. If the integrated current value (Q) is less than or equal to ΔQ, the controller determines that it is not possible to secure the number of measurement data corresponding to ΔQ (the determination flow in step S7 is "No"), and the controller terminates the control flow shown in Figure 11 and executes the control flow again from step S1.

[0048] If the controller 10 determines that the integrated current value (Q) is greater than ΔQ, the controller 10 determines that the electrical double layer capacitance C ｄｌ [x] is the electrical double layer capacitance C ｄｌ Determine whether it is less than [0]. Electrical double layer capacitance C ｄｌ [x] is the electrical double layer capacitance C ｄｌ If the value is [0] or greater, the electric double layer capacity is increasing, and the secondary battery 1 is in the early stages of deterioration (the judgment flow in step S8 is "No"). The controller 10 terminates the control flow shown in Figure 11 and executes the control flow again from step S1. Electric double layer capacity C ｄｌ [x] is the electrical double layer capacitance C ｄｌ If the value is less than [0], the electric double-layer capacity is decreasing, and the state of the secondary battery 1 is beyond the early stages of degradation (the judgment flow in step S8 is "Yes"). In step S9, the controller 10 sets the estimated state variable (S) to "1". The controller 10 terminates the control flow shown in Figure 11 and executes the control flow again from step S1.

[0049] In the determination flow of step S6, if it is determined that the estimated state variable (S) is not zero, the controller 10 determines whether the estimated state variable (S) is "1" (step S10). If it is determined that the estimated state variable (S) is not "1", the controller 10 terminates the control flow shown in Figure 11 and executes the control flow again from step S1.

[0050] If the estimated state variable (S) is "1", the battery state estimation unit 12 determines Q[0] to Q[x-1] and C ｄｌ [0] to C ｄｌ An approximation curve is calculated based on the data set [x-1]. The battery state estimation unit 12 calculates the current electric double layer capacitance C from the approximation curve. ｄｌ Predicted value (Current predicted value: C) ｄｌ＿ｐ Step S11 predicts the current estimated value (C). In step S12, the battery state estimation unit 12 predicts the current estimated value (C). ｄｌ [x) is within the specified range (C ｄｌ＿ｐ ±Δ ｄｌ Determine whether or not it is within the parentheses.

[0051] Current estimate (C ｄｌ [x) is within the specified range (C ｄｌ＿ｐ ±Δ ｄｌ If it is determined that the battery state is outside of the specified range, the battery state estimation unit 12 will determine the current estimated value (C ｄｌ The system determines that [x] is an outlier and resets the loop count [x] to x-1 (step S13). This ensures that if the current measurement data is an outlier, the current measurement data is discarded. Current estimated value (C ｄｌ [x) is within the specified range (C ｄｌ ±Δ ｄｌ If it is determined that the battery state is within the range, the battery state estimation unit 12 uses the correlation between electric double layer capacitance and crack amount to determine the current estimated value (C ｄｌ The amount of crack is estimated based on [x] (step S14). The controller 10 terminates the control flow shown in Figure 11. Note that if the amount of crack has been estimated, the controller 10 may terminate the control flow without executing the control flow again from step S1.

[0052] As described above, the battery state estimation device or battery state estimation method according to this embodiment measures the impedance (Z) of the secondary battery 1 and calculates the electric double layer capacitance (C) based on the impedance (Z). ｄｌ ) or reaction resistance (R ｃｔ Estimate at least one of the following: the electrical double layer capacitance (C ｄｌ The smaller the value of ), the greater the amount of structural change (crack amount). Using the correlation between electrical double layer capacitance and structural change (crack amount), the estimated electrical double layer capacitance (C) ｄｌ The amount of structural change (amount of cracks) is estimated based on ), or the reaction resistance (R ｃｔ The larger the reaction resistance (R), the greater the structural change (amount of cracking). Using the correlation between reaction resistance and structural change (amount of cracking), the estimated reaction resistance (R) ｃｔ The amount of structural change (amount of cracking) is estimated based on the following. This allows the amount of structural change (amount of cracking) to be estimated without disassembling the battery, using parameters calculated based on impedance. As a result, the amount of structural change can be estimated.

[0053] In this embodiment, the battery state estimation unit 12 calculates the cumulative amount of charge and discharge current of the secondary battery 1. If the cumulative amount of charge and discharge current is equal to or greater than a predetermined cumulative amount threshold, it determines that the secondary battery 1 is in the early stages of degradation or beyond. When it is determined that the secondary battery 1 is in the early stages of degradation or beyond, it estimates the amount of structural change (crack amount) based on the correlation between the electric double layer capacity and the amount of structural change (crack amount), or the correlation between the reaction resistance and the amount of structural change (crack amount). In other words, in this embodiment, the behavior of the electric double layer capacity and reaction resistance differs between the early stages of degradation and the later stages of degradation, so the determination of whether it is the early stages of degradation or beyond is made using the cumulative value of the charge and discharge current. This makes it possible to determine whether it is the early stages of degradation or the later stages of degradation, even when the same electric double layer capacity or reaction resistance is estimated for different degradation states, and prevents a decrease in the estimation accuracy of the amount of structural change (crack amount).

[0054] In this embodiment, the battery state estimation unit 12 calculates the electric double layer capacitance (C ｄｌ ) is on a downward trend, and / or the reaction resistance (R ｃｔ ) determines whether there is an increasing trend, and electric double layer capacitance (Cｄｌ ) is on a downward trend, and the reaction resistance (R ｃｔ If it is determined that the electrical double layer capacitance is increasing or at least one of the two is increasing, the structural change (crack amount) is estimated based on the correlation between electrical double layer capacitance and structural change (crack amount), or the correlation between reaction resistance and structural change (crack amount). In other words, in this embodiment, the behavior of electrical double layer capacitance and reaction resistance differs in the early stages of degradation from that of later stages, so it is determined whether it is the early stages of degradation or later based on whether the electrical double layer capacitance or reaction resistance is increasing or decreasing. This makes it possible to determine whether it is the early stages of degradation or later, even when the same electrical double layer capacitance or reaction resistance is estimated for different degradation states, and prevents a decrease in the estimation accuracy of the structural change (crack amount) compared to determining it by the integrated current.

[0055] In this embodiment, the battery state estimation unit 12 is determined to have an electric double layer capacitance (C ｄｌ Based on the historical estimates of the electrical double layer capacitance (C), ｄｌ Predict the current predicted value of ) and, based on impedance (Z), calculate the electrical double layer capacitance (C). ｄｌ The current estimated value of the electrical double layer capacitance is estimated, and if the difference between the current estimated value and the current predicted value is greater than a predetermined difference threshold, the current estimated value is not used to estimate the structural change amount (crack amount). If the difference between the current estimated value and the current predicted value is less than or equal to the difference threshold, the current estimated value is used to estimate the structural change amount (crack amount). In other words, in this embodiment, a predicted value is predicted from the history of estimated values ​​of the electrical double layer capacitance, and it is determined whether the estimated value of the electrical double layer capacitance estimated from impedance (Z) deviates from the predicted value by more than a predetermined value. If it is within the predetermined value, the estimated value of the electrical double layer capacitance is used to estimate the structural change amount (crack amount). As a result, even if the estimated value of the electrical double layer capacitance becomes an abnormal value due to noise during impedance measurement, the abnormal value can be excluded, thus preventing the estimated value of the crack amount from becoming an abnormal value.

[0056] In this embodiment, the battery state estimation unit 12 has a reaction resistance (R ｃｔ Based on the history of estimated values ​​of ), the reaction resistance (R ｃｔ Predict the current predicted value of ) and, based on the impedance (Z), calculate the response resistance (R).ｃｔ The current estimated value of the reaction resistance is estimated, and if the difference between the current estimated value and the current predicted value is greater than a predetermined difference threshold, the current estimated value is not used to estimate the structural change amount (crack amount). If the difference between the current estimated value and the current predicted value is less than or equal to the difference threshold, the current estimated value is used to estimate the structural change amount (crack amount). In other words, in this embodiment, a predicted value is calculated from the history of estimated values ​​of the reaction resistance, and it is determined whether the estimated value of the reaction resistance estimated from the impedance (Z) deviates from the predicted value by more than a predetermined value. If it is within the predetermined value, the estimated value of the reaction resistance is used to estimate the structural change amount (crack amount). This makes it possible to exclude abnormal values ​​even if the estimated value of the reaction resistance becomes an abnormal value due to noise during impedance measurement, thus preventing the estimated value of the structural change amount (crack amount) from becoming an abnormal value.

[0057] In this embodiment, the battery state estimation unit 12 is determined to have an electric double layer capacitance (C ｄｌ Estimated value of ) and reaction resistance (R ｃｔ If the combination of estimated values ​​of ) falls outside the predetermined range, then the electric double layer capacitance (C) ｄｌ ) Estimated value or reaction resistance (R ｃｔ The estimated value of ) is not used to estimate the amount of structural change (amount of cracks), and the electrical double layer capacitance (C) is not used. ｄｌ Estimated value of ) and reaction resistance (R ｃｔ If the combination of estimated values ​​of ) falls within a predetermined range, then the electric double layer capacitance (C) ｄｌ ) Estimated value or reaction resistance (R ｃｔ In this embodiment, the estimated values ​​of the electrical double layer capacitance and electrical double layer capacitance are used to estimate the amount of structural change (amount of cracking). In other words, in this embodiment, the reaction resistance and electrical double layer capacitance change within a predetermined range depending on the state of deterioration. If the values ​​fall outside that range, it means that the electrical double layer capacitance or reaction resistance is an abnormal value, and therefore it is not used to estimate the amount of structural change (amount of cracking). Instead, the electrical double layer capacitance and reaction resistance that are within the range are used to estimate the amount of structural change (amount of cracking). This prevents the estimated value of the amount of structural change (amount of cracking) from becoming abnormal even when abnormal values ​​occur that are difficult to detect by using only past historical data, such as when the values ​​gradually shift due to sensor deterioration.

[0058] In this embodiment, the control flow of the battery state estimation method shown in Figure 11 is the electric double layer capacitance C ｄｌ The amount of cracking was estimated from the reaction resistance R. ｃｔ The amount of cracking can also be estimated from this. Furthermore, the control flow of the battery state estimation method shown in Figure 11 can be modified as follows: Reaction resistance R ｃｔ When estimating the amount of cracks from the reaction resistance R, in the control flow of step S8, the controller 10 controls the reaction resistance R ｃｔ [x] is the reaction resistance R ｃｔ It is determined whether it is greater than [0] or not. Also, in the control flow of step S11, the controller 10 controls Q[0] to Q[x-1] and R ｃｔ [0] to R ｃｔ An approximation curve is calculated based on the data set [x-1]. Then, the battery state estimation unit 12 calculates the current reaction resistance R from the approximation curve. ｃｔ Predicted value (current predicted value: R ｃｔ＿ｐ ) predicts. In the control flow of step S12, the battery state estimation unit 12 predicts the current estimated value (R ｃｔ [x]) is within a predetermined range (R ｃｔ＿ｐ ±ΔR ｃｔ It determines whether or not it is within the range. In the control flow of step S14, the battery state estimation unit 12 uses the correlation between reaction resistance and crack amount to determine the current estimated value (R ｃｔ The amount of cracking is estimated based on [x]).

[0059] In this embodiment, the measurement unit 11 corresponds to the "impedance measurement unit" of the present invention.

[0060] <Second Embodiment> Next, a battery state estimation system according to the second embodiment will be described. In this embodiment, a part of the control processing of the controller 10 differs from that of the first embodiment. In the following description, the parts that differ from the first embodiment will be described, but the configuration other than the differing parts is the same as that of the first embodiment described above, and the description in the first embodiment will be appropriately referenced for the configuration that is the same as that of the first embodiment. In this embodiment, the objective is to estimate the amount of change in crystal structure as an indicator of the degree of degradation when the positive electrode active material deteriorates due to a change in crystal structure.

[0061] Figure 12 shows the electric double layer capacitance (C) of the secondary battery 1. ｄｌ Figure 12 is a graph showing the correlation between the electric double layer capacitance (C) and the amount of change in crystal structure from experimental data of secondary battery 1. ｄｌ Figure 13 shows the reaction resistance (R) of secondary battery 1. The graph plots the data of the change in crystal structure and approximates it. As shown in Figure 12, the smaller the electric double layer capacitance, the greater the change in the crystal structure of the positive electrode active material. ｃｔ Figure 13 is a graph showing the correlation between the reaction resistance (R) and the amount of change in crystal structure from experimental data of secondary battery 1. ｃｔ This graph plots the data on the reaction resistance and the amount of change in crystal structure, and shows an approximate curve. As shown in Figure 13, the greater the reaction resistance, the greater the change in the crystal structure of the positive electrode active material.

[0062] The battery state estimation unit 12 stores in memory a map showing the correlation between electric double layer capacitance and crystal structure change, or a map showing the correlation between reaction resistance and crystal structure change. By referring to the map, it estimates the value corresponding to the estimated electric double layer capacitance as the crystal structure change, or estimates the value corresponding to the estimated reaction resistance as the crystal structure change. For example, if the electric double layer capacitance estimated based on impedance (Z) is Cdl ＿ｂ In this case, the battery state estimation unit 12 calculates the electric double layer capacitance (Cdl) from the graph showing the correlation between electric double layer capacitance and crystal structure change (corresponding to the dotted line graph in Figure 12). ＿ｂ ) corresponds to the change in crystal structure (Cs ＿ｂ We estimate the following.

[0063] As described above, the battery state estimation device or battery state estimation method according to this embodiment measures the impedance (Z) of the secondary battery 1 and calculates the electric double layer capacitance (C) based on the impedance (Z). ｄｌ ) or reaction resistance (R ｃｔ Estimate at least one of the following: the electrical double layer capacitance (C ｄｌ The smaller the value of ), the greater the structural change (crystal structure change). Using the correlation between electric double layer capacitance and structural change (crystal structure change), the estimated electric double layer capacitance (C) ｄｌ The amount of structural change (amount of crystal structure change) is estimated based on ), or the reaction resistance (Rｃｔ The larger the reaction resistance (R), the greater the structural change (crystal structure change). Using the correlation between reaction resistance and structural change (crystal structure change), the estimated reaction resistance (R) ｃｔ The amount of structural change (crystal structure change) is estimated based on the following. This allows the amount of structural change (crystal structure change) of the positive electrode active material to be estimated without disassembling the battery, using parameters calculated based on impedance. As a result, the amount of structural change of the positive electrode active material can be estimated.

[0064] In this embodiment, the battery state estimation unit 12 calculates the cumulative amount of charge and discharge current of the secondary battery 1. If the cumulative amount of charge and discharge current is equal to or greater than a predetermined cumulative amount threshold, it determines that the degradation of the secondary battery 1 is beyond the initial stage. If it determines that the degradation of the secondary battery 1 is beyond the initial stage, it may estimate the amount of structural change (crystal structure change) based on the correlation between electric double layer capacity and structural change (crystal structure change), or the correlation between reaction resistance and structural change (crystal structure change). The method for determining whether or not the degradation is beyond the initial stage may be the same as the determination method described in the first embodiment.

[0065] In this embodiment, the battery state estimation unit 12 may exclude abnormal values ​​if the estimated values ​​of the electric double layer capacitance and / or reaction resistance show abnormal values. The method for determining abnormal values ​​and the method for excluding abnormal values ​​may be the same as the determination method described in the first embodiment.

[0066] In this embodiment, the battery state estimation unit 12 calculates the electric double layer capacitance (C ｄｌ ) is on a downward trend, and / or the reaction resistance (R ｃｔ ) determines whether there is an increasing trend, and electric double layer capacitance (C ｄｌ ) is on a downward trend, and the reaction resistance (R ｃｔ If it is determined that the electrical double layer capacitance (C) is increasing, or at least one of the two is increasing, the structural change (crystal structure change) may be estimated based on the correlation between electrical double layer capacitance and structural change (crystal structure change), or the correlation between reaction resistance and structural change (crystal structure change). ｄｌ ) is on a downward trend, and / or the reaction resistance (R ｃｔThe method for determining whether or not the number is on an increasing trend may be the same as the determination method described in the first embodiment.

[0067] In this embodiment, the battery state estimation unit 12 is determined to have an electric double layer capacitance (C ｄｌ Based on the historical estimates of the electrical double layer capacitance (C), ｄｌ Predict the current predicted value of ) and, based on impedance (Z), calculate the electrical double layer capacitance (C). ｄｌ The current estimated value of ) is estimated, and if the difference between the current estimated value and the current predicted value is greater than a predetermined difference threshold, the current estimated value is not used to estimate the structural change amount (crystal structure change amount). If the difference between the current estimated value and the current predicted value is less than or equal to the difference threshold, the current estimated value may be used to estimate the structural change amount (crystal structure change amount). Electric double layer capacitance (C ｄｌ Method for predicting the current predicted value of ), electric double layer capacitance (C ｄｌ The method for estimating the current estimated value of ) may be the same as the determination method described in the first embodiment.

[0068] In this embodiment, the battery state estimation unit 12 has a reaction resistance (R ｃｔ Based on the history of estimated values ​​of ), the reaction resistance (R ｃｔ Predict the current predicted value of ) and, based on the impedance (Z), calculate the response resistance (R). ｃｔ The current estimated value of ) is estimated, and if the difference between the current estimated value and the current predicted value is greater than a predetermined difference threshold, the current estimated value is not used to estimate the structural change amount (crystal structure change amount). If the difference between the current estimated value and the current predicted value is less than or equal to the difference threshold, the current estimated value may be used to estimate the structural change amount (crystal structure change amount). Reaction resistance (R ｃｔ Method for predicting the current predicted value of ), reaction resistance (R ｃｔ The method for estimating the current estimated value of ) may be the same as the determination method described in the first embodiment.

[0069] In this embodiment, the battery state estimation unit 12 is determined to have an electric double layer capacitance (C ｄｌ Estimated value of ) and reaction resistance (R ｃｔ If the combination of estimated values ​​of ) falls outside the predetermined range, then the electric double layer capacitance (C) ｄｌ ) Estimated value or reaction resistance (R ｃｔThe estimated value of ) is not used to estimate the structural change (crystal structure change), and the electric double layer capacitance (C) is not used. ｄｌ Estimated value of ) and reaction resistance (R ｃｔ If the combination of estimated values ​​of ) falls within a predetermined range, then the electric double layer capacitance (C) ｄｌ ) Estimated value or reaction resistance (R ｃｔ The estimated value of ) may be used to estimate the structural change (crystal structure change). Note that the electric double layer capacitance (C) ｄｌ Estimated value of ) and reaction resistance (R ｃｔ The method for determining whether the combination of estimated values ​​of ) is outside a predetermined range may be the same as the determination method described in the first embodiment.

[0070] In this embodiment, the battery state estimation unit 12 uses the correlation between electric double layer capacity and crack amount, and the correlation between electric double layer capacity and crystal structure change amount to estimate the electric double layer capacity (C ｄｌ The amount of cracks and the amount of change in crystal structure may be estimated based on the following. For example, the battery state estimation unit 12 estimates the electric double layer capacitance (C) based on the impedance (Z). ｄｌ ) is estimated, and the electrical double layer capacitance (C) is calculated. ｄｌ The amount of cracks and the amount of change in crystal structure that correspond to the estimated value of ) can be identified from the correlation shown in the graphs in Figures 4 and 12. As shown in the graphs in Figures 4 and 12, the amount of cracks and the amount of change in crystal structure are related to the electric double layer capacitance (C). ｄｌ ) is changing with different characteristics. Therefore, the battery state estimation unit 12 determines the electric double layer capacitance (C ｄｌ For a given estimate, it is possible to obtain an estimation result such as one in which the amount of cracks is small but the amount of change in crystal structure is large. In other words, the battery state estimation unit 12 only needs to estimate at least one of the amount of cracks in the positive electrode active material and the amount of change in crystal structure as the amount of change in structure.

[0071] 1...Secondary battery 2...DC-DC converter 3...Voltage sensor 4...Current sensor 5...Impedance meter 10...Controller 11...Measurement unit 12...Battery state estimation unit

Claims

1. A battery state estimation device for estimating the state of a battery, comprising: an impedance measurement unit for measuring the impedance (Z) of the battery; and a battery state estimation unit for estimating the state of the battery, wherein the battery state estimation unit estimates at least one of the electric double layer capacitance of the positive electrode of the battery or the reaction resistance of the positive electrode based on the impedance (Z); estimates the amount of structural change of the positive electrode active material based on the estimated electric double layer capacitance using the correlation between the electric double layer capacitance and the amount of structural change, where a smaller electric double layer capacitance results in a larger amount of structural change of the positive electrode active material; or estimates the amount of structural change of the positive electrode active material based on the estimated reaction resistance using the correlation between the reaction resistance and the amount of structural change, where a larger reaction resistance results in a larger amount of structural change of the positive electrode active material.

2. A battery state estimation device according to claim 1, wherein the battery state estimation unit calculates the cumulative amount of the charge and discharge current of the battery, determines that the battery is beyond the initial stage of deterioration if the cumulative amount of the charge and discharge current is equal to or greater than a predetermined cumulative amount threshold, and estimates the amount of structural change of the positive electrode active material based on the correlation between the electric double layer capacity and the amount of structural change, or the correlation between the reaction resistance and the amount of structural change.

3. A battery state estimation device according to claim 1, wherein the battery state estimation unit determines whether the electric double layer capacity is decreasing and / or whether the reaction resistance is increasing, and when it is determined that the electric double layer capacity is decreasing and / or the reaction resistance is increasing, the battery state estimation device estimates the amount of structural change of the positive electrode active material based on the correlation between the electric double layer capacity and the amount of structural change, or the correlation between the reaction resistance and the amount of structural change.

4. A battery state estimation device according to any one of claims 1 to 3, wherein the battery state estimation unit predicts the current predicted value of the electric double layer capacity based on the history of the estimated value of the electric double layer capacity, estimates the current estimated value of the electric double layer capacity based on the impedance (Z), and if the difference between the current estimated value and the current predicted value is greater than a predetermined difference threshold, the current estimated value is not used to estimate the amount of structural change of the positive electrode active material, and if the difference between the current estimated value and the current predicted value is less than or equal to the difference threshold, the current estimated value is used to estimate the amount of structural change of the positive electrode active material.

5. A battery state estimation device according to any one of claims 1 to 3, wherein the battery state estimation unit predicts the current predicted value of the reaction resistance based on the history of the estimated value of the reaction resistance, estimates the current estimated value of the reaction resistance based on the impedance (Z), and if the difference between the current estimated value and the current predicted value is greater than a predetermined difference threshold, the current estimated value is not used to estimate the amount of structural change of the positive electrode active material, and if the difference between the current estimated value and the current predicted value is less than or equal to the difference threshold, the current estimated value is used to estimate the amount of structural change of the positive electrode active material.

6. A battery state estimation device according to any one of claims 1 to 3, wherein the battery state estimation unit, when the combination of the estimated value of the electric double layer capacity and the estimated value of the reaction resistance is outside a predetermined region, does not use the estimated value of the electric double layer capacity or the estimated value of the reaction resistance to estimate the amount of structural change of the positive electrode active material; when the combination of the estimated value of the electric double layer capacity and the estimated value of the reaction resistance is within the predetermined region, uses the estimated value of the electric double layer capacity or the estimated value of the reaction resistance to estimate the amount of structural change of the positive electrode active material; and the predetermined region is set on a map showing the correspondence between the electric double layer capacity and the reaction resistance.

7. A battery state estimation device according to any one of claims 1 to 3, wherein the battery state estimation unit estimates at least one of the amount of cracks in the positive electrode active material and the amount of change in crystal structure as the amount of structural change.

8. A battery state estimation method performed by a controller for estimating the state of a battery, wherein the controller measures the impedance (Z) of the battery, estimates at least one of the electric double layer capacitance of the positive electrode or the reaction resistance of the positive electrode based on the impedance (Z), estimates the amount of structural change of the positive electrode active material based on the estimated electric double layer capacitance using the correlation between the electric double layer capacitance and the amount of structural change, where a smaller electric double layer capacitance results in a larger amount of structural change of the positive electrode active material, or estimates the amount of structural change of the positive electrode active material based on the estimated reaction resistance using the correlation between the reaction resistance and the amount of structural change, where a larger reaction resistance results in a larger amount of structural change of the positive electrode active material.

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