Battery degradation diagnosis method and battery degradation diagnosis device

Abstract

To provide a method for appropriately determining whether or not cell pressurizing force is to be increased.SOLUTION: A battery deterioration diagnosis method for determining whether or not a change in cell pressure is required in a pressure mechanism that applies cell pressure in the stacking direction to a battery stack having a plurality of stacked power generation elements cause a controller to execute calculating an electric double layer capacity on the basis of a change in current value when a voltage changes due to switching between charging and discharging of the power generation elements, estimating an increase or decrease in effective interfacial area relative to a normal state on the basis of the electric double layer capacity, and determining that the cell pressure needs to be increased when it is estimated that the effective interfacial area has decreased, and determining that the cell pressure does not need to be changed when it is estimated that the effective interfacial area has not decreased.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery degradation diagnosis method and device for determining whether or not a pressure force of a pressure mechanism that applies pressure to a battery stack including a plurality of stacked power generating elements in the stacking direction needs to be changed. [Background technology]

[0002] To ensure the area of ​​the interface between the electrolyte and electrodes of a secondary battery (hereinafter also referred to as the effective interfacial area), a method is known in which a pressure mechanism that can apply pressure to the battery stack in the stacking direction is used, and the applied pressure is varied depending on the deterioration state of the secondary battery. For example, if peeling occurs between the active material and the electrolyte due to repeated charge and discharge, reducing the effective interfacial area, increasing the applied pressure (hereinafter also referred to as the cell pressure) can improve adhesion between the active material and the electrolyte and restore the effective interfacial area. However, unnecessary increases in the cell pressure can lead to short circuits due to creep-induced extrusion of electrode material or the formation of dendrites. Therefore, in this method, it is important to accurately grasp the deterioration state of the secondary battery. Patent Document 1 discloses a method for diagnosing the deterioration state of a secondary battery using AC impedance measured by an AC impedance method as a parameter. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 255557 Summary of the Invention [Problem to be solved by the invention]

[0004] However, AC impedance is the sum of the resistances of the positive and negative electrodes, and factors other than the effective interfacial area (e.g., chemical degradation of the electrode material) also affect its increase or decrease. Therefore, if the deterioration diagnosis method described in the above document determines that deterioration is occurring based on an increase in AC impedance and increases the cell pressure, there is a risk of the aforementioned short circuit occurring if the increase in AC impedance is caused by factors other than the effective interfacial area. In other words, the method described in the above document cannot determine whether the effective interfacial area is decreasing, making it difficult to appropriately determine whether the cell pressure should be increased.

[0005] Therefore, an object of the present invention is to provide a method for appropriately determining whether or not the cell pressurizing force should be increased. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a battery degradation diagnosis method for determining whether or not a change in cell pressure is required in a pressure mechanism that applies cell pressure in the stacking direction to a battery stack having a plurality of stacked power-generating elements. In this method, a controller calculates an electric double layer capacity based on a change in current value during a voltage change accompanying switching between charging and discharging of the power-generating elements, estimates an increase or decrease in effective interfacial area relative to a normal state based on the electric double layer capacity, and determines that the cell pressure needs to be increased if it is estimated that the effective interfacial area has decreased, and determines that the cell pressure does not need to be changed if it is estimated that the effective interfacial area has not decreased. [Effects of the Invention]

[0007] According to the above aspect, it is possible to appropriately determine whether or not the cell pressurizing force should be increased. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a battery control system. [Figure 2] FIG. 2 is a schematic diagram of a secondary battery. [Figure 3]FIG. 3 is a schematic diagram of a three-dimensional electrode for explaining the mechanism of battery deterioration. [Figure 4] FIG. 4 is a time chart of voltage and current when charging and discharging are switched. [Figure 5] FIG. 5 is a diagram showing the difference in electric double layer capacity Cdl due to the difference in cell pressure. [Figure 6] FIG. 6 is a flowchart of the deterioration diagnosis. [Figure 7] FIG. 7 is a diagram showing the relationship between charge / discharge and volume expansion / contraction. [Figure 8] FIG. 8 is a graph showing the relationship between the SOC and the electric double layer capacity Cdl. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] 1 is a schematic diagram of a battery control system 100 that performs deterioration diagnosis according to an embodiment of the present invention. FIG. 2 is a schematic diagram of a secondary battery 1 included in the battery control system 100.

[0011] The battery control system 100 includes a secondary battery 1 and a battery controller (hereinafter simply referred to as the “controller”) 2.

[0012] The secondary battery 1 is, for example, a known lithium deposition type all-solid-state battery. The secondary battery 1 includes a battery stack 11 in which a plurality of power generating elements 10 are stacked, and a pressure mechanism 20 that applies a cell pressure to the battery stack 11 in the stacking direction.

[0013] The pressure mechanism 20 includes an upper end plate 12 that contacts the power generation element 10 at the upper end of the battery stack 11, a lower end plate 13 that contacts the power generation element 10 at the lower end of the battery stack 11, multiple shafts 14 that connect the upper end plate 12 and the lower end plate 13, and an adjustment mechanism 15 that adjusts the cell pressure. The adjustment mechanism 15 includes, for example, a thread groove on the shaft 14 and a nut that engages with the thread groove, and adjusts the cell pressure by the tightness of the nut. The cell pressure can be set arbitrarily depending on the power generation element 10 used, and is set to a magnitude that maintains good contact between the layers of the power generation element 10. Note that an elastic member such as a spring may be added to the adjustment mechanism 15 to absorb volume changes due to expansion and contraction of the electrodes, or the controller 2 may adjust the cell pressure using an actuator or the like.

[0014] The battery control system 100 also includes a temperature sensor 3 that detects the temperature of the secondary battery 1, a current sensor 4 that detects the input / output current of the secondary battery 1, and a voltage sensor 5 that detects the voltage of the secondary battery 1. A plurality of temperature sensors 3 are provided to obtain the temperature distribution within the surface of the power generating element 10.

[0015] The controller 2 reads the detected values ​​of the temperature sensor 3, current sensor 4, and voltage sensor 5, and performs various known controls such as managing the SOC (State of Charge) and controlling charging and discharging, as well as performing a deterioration diagnosis (described later). The controller 2 is composed of a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and an input / output interface (I / O interface). The controller 2 can also be composed of multiple microcomputers.

[0016] For the deterioration diagnosis, the controller 2 includes an electric double layer capacity (Cdl) calculation unit 2A, an increase / decrease estimation unit that estimates an increase / decrease in the effective interfacial area, and a deterioration diagnosis unit 2C that diagnoses the degree of deterioration of the secondary battery 1 based on the increase / decrease in the effective interfacial area.

[0017] The deterioration that is the subject of the deterioration diagnosis will be described with reference to FIG.

[0018] FIG. 3 is a schematic diagram of an electrode having a three-dimensional structure (hereinafter also referred to as a three-dimensional electrode), with the left diagram showing a normal state and the right diagram showing a deteriorated state.

[0019] The deterioration that is the subject of deterioration diagnosis in this embodiment is a decrease in the effective interfacial area between the electrolyte and the active material. This decrease in effective interfacial area occurs when the electrolyte and active material, which are normally in close contact, become at least partially separated as a result of repeated charge and discharge, as shown in areas A and B in the right diagram. Even if such separation occurs, it may be possible to restore the effective interfacial area by increasing the cell pressure to bring the separated active material and electrolyte into close contact.

[0020] However, it is difficult to directly detect the effective interfacial area. Furthermore, since a decrease in the effective interfacial area increases the interfacial resistance between the electrode and the electrolyte, it is conceivable that a decrease in the effective interfacial area can be detected using AC impedance as a parameter. However, as mentioned above, AC impedance is also affected by chemical degradation of the electrode material, etc., so an increase in AC impedance does not necessarily mean that the effective interfacial area has decreased.

[0021] Therefore, in this embodiment, the electric double layer capacitance Cdl is used as a parameter to diagnose whether the effective interfacial area has decreased by the method described below, and the cell pressure is adjusted based on the diagnosis result.

[0022] [Deterioration diagnosis method] Controller 2, more specifically, C dl The calculation unit 2A switches between charging and discharging at a predetermined potential sweep rate, and calculates the electric double layer capacity based on the amount of change in current value when the voltage changes due to switching between charging and discharging. This will be described with reference to Figures 4 and 5.

[0023] Figure 4 shows the time chart of the voltage and current when switching between charge and discharge. Figure 5 shows the change in the electric double layer capacity C dl FIG.

[0024] The current i detected by the current sensor 4 is the Faraday current i f and the electric double layer charge / discharge current i dl Therefore, in Figure 4, the current value is the Faraday current i f and the electric double layer charge / discharge current i dl The Faraday current i f and the electric double layer charge / discharge current i dl Since it is not possible to directly detect the values ​​of , the chart in Figure 4 shows estimated values ​​that take into account the characteristics of each.

[0025]

number

[0026] Voltage E ≒ equilibrium potential E eq In this case, the Faraday current i f is the overvoltage (i.e., EE eq ) (Equation (2)). In equation (2), i0 is the exchange current density, n is the number of reaction electrons (the number of electrons involved in the reaction), F is the Faraday constant, R is the gas constant, and T is the absolute temperature.

[0027]

number

[0028] On the other hand, the electric double layer charge / discharge current i dl is proportional to the potential sweep rate v (Equation (3)).

[0029]

number

[0030] As shown in equation (3), in the case of a three-dimensional electrode, the electric double layer capacitance Cdl is also considered as a function of the potential sweep rate v. This is because when the potential sweep rate v is fast, the calculated electric double layer capacitance Cdl represents the capacitance of a portion of the electrode layer, and when the potential sweep rate v approaches zero, it represents the capacitance of the entire electrode layer. In this embodiment, the deterioration diagnosis is performed using the capacitance of the entire electrode layer.

[0031] The potential sweep rate v is set in advance, so the electric double layer charge / discharge current i dl If this is known, the electric double layer capacitance C can be calculated from equation (3). dl As described above, the current i detected by the current sensor 4 is the Faraday current i f and the electric double layer charge / discharge current i dl and the Faraday current i f and the electric double layer charge / discharge current i dl Although the individual values ​​of i cannot be directly detected, their behavior can be estimated as shown in Figure 4. f and the electric double layer charge / discharge current i dl When the charge / discharge cycle is switched (i.e., when the voltage E changes between increasing and decreasing), the Faraday current i f does not change, and the electric double layer charge / discharge current i dl The sign of is reversed. Therefore, the change in current i at this timing is 2i dl Since the absolute value of this change remains the same but the sign is reversed, halving the change in current i will result in the electric double layer charge / discharge current i dl can be identified.

[0032] C dl The calculation unit 2A calculates the electric double layer charge / discharge current i dl From equation (3), the electric double layer capacitance C dl Calculate.

[0033] FIG. 5 shows the electric double layer capacity C dl The vertical axis shows the electric double layer capacitance C dlThe horizontal axis represents the potential sweep rate v, and black circles represent the case where the cell pressure is high, and white circles represent the case where the cell pressure is low.

[0034] As shown in the figure, the electric double layer capacity C is higher when the cell pressure is high than when the cell pressure is low. dl The difference becomes more significant as the potential sweep rate v approaches zero.

[0035] When two different cell pressures, high and low, are applied to the same secondary battery 1, it can be estimated that the effective interfacial area is larger when the cell pressure is high than when the cell pressure is low.

[0036] Therefore, the electric double layer capacitance C dl There is a correlation between the electric double layer capacitance and the effective interfacial area, dl It can be assumed that the larger the effective interfacial area, the larger the electric double layer capacity C of the secondary battery 1 in a normal state. dl If this is known, the electric double layer capacitance C calculated by the above method can be calculated. dl The increase / decrease estimation unit 2B estimates the increase / decrease in the effective interfacial area by this method.

[0037] Then, based on the result of the estimation by the increase / decrease estimation unit 2B, the deterioration diagnosis unit 2C determines whether or not to increase the cell pressure. That is, if it is estimated that the effective interfacial area has decreased, it determines that it is necessary to increase the cell pressure, and if it is estimated that it has not decreased, it determines that it is not necessary to increase the cell pressure. In this way, the electric double layer capacitance C, which is correlated with the effective interfacial area, dl By determining whether the effective interfacial area is reduced using the above formula, it is possible to appropriately determine whether to increase the cell pressure.

[0038] Next, a specific control routine for the deterioration diagnosis will be described with reference to FIG.

[0039] 6 is a flowchart showing an example of a control routine for deterioration diagnosis and operations according to the diagnosis results. The following will explain each step.

[0040] In step S100, the controller 2 determines whether the temperature distribution in the cell surface of the battery stack 11 is equal to or less than a fourth threshold value set in advance. If it is equal to or less than the fourth threshold value, the process of step S101 is executed. If it is greater than the fourth threshold value, the routine is terminated. This step is for determining whether the state is such that deterioration can be diagnosed accurately. As described above, in this embodiment, the electric double layer charge / discharge current i is calculated based on the difference in current i at the time of switching between charge and discharge. dl As can be seen from equation (1) and Figure 4, most of the current i is the Faraday current i f and the Faraday current i f As shown in equation (2), depends on the temperature T. Therefore, when the temperature distribution in the cell surface is large (for example, during fast charging), it is difficult to accurately calculate the electric double layer charge / discharge current i dl Therefore, in this step, we accurately estimate the electric double layer charge / discharge current i dl In cases where it is not possible to estimate the risk, it is decided not to make a diagnosis.

[0041] The fourth threshold is the electric double layer charge / discharge current i dl The influence of temperature distribution on the estimation is obtained by experiment or the like, and the range is arbitrarily set within the range where the estimation accuracy is within the allowable range.

[0042] In step S101, the controller 2 determines whether the secondary battery 1 is in a state where charging and discharging are possible. If charging and discharging are possible, the process of step S102 is executed. If not, the routine ends. This step is for determining whether switching between charging and discharging for degradation diagnosis is possible. Charging of the secondary battery 1 is restricted when it is close to fully charged, and discharging is restricted when it is close to fully discharged. For this reason, for example, if degradation diagnosis is performed when the secondary battery 1 is in a fully charged state, discharging is possible, but the restriction is immediately imposed as soon as charging is switched over. Therefore, in this step, it is determined that charging and discharging are possible if the SOC of the secondary battery 1 is within a range where the above restriction does not apply even when switching between charging and discharging for degradation diagnosis is performed, but that charging and discharging are not possible if it is outside this range.

[0043] In step S102, the controller 2 records the current SOC of the secondary battery 1. The SOC may be estimated by a known method (for example, a current integration method).

[0044] In step S103, the controller 2 starts measuring the battery temperature T, the cell voltage E, and the current i, and also starts measuring the time t from the start of the measurements.

[0045] In step S104, the controller 2 determines whether a predetermined time has elapsed since the charge / discharge switching, and if so, executes the process of step S105, and if not, ends this routine. In other words, the controller 2 repeatedly executes the processes of steps S100 to S104 until the predetermined time has elapsed since the charge / discharge switching, and if so, executes the process of step S105. The predetermined time here is determined by the above-mentioned electric double layer charge / discharge current i dl The specific value can be set arbitrarily depending on the potential sweep rate v, the structure of the power generating element 10, etc.

[0046] In step S105, the controller 2 ends the measurement of each value that began in step S103.

[0047] In step S106, the controller 2 determines whether the change amount ΔT of the battery temperature T during measurement (hereinafter also referred to as the temperature change amount) is equal to or less than the third threshold value. If it is equal to or less than the third threshold value, the controller 2 executes the process of step S107. If it is greater than the third threshold value, the controller 2 ends this routine. As described above, the battery temperature T is calculated based on the electric double layer charge / discharge current i dl Therefore, the larger the temperature change ΔT during measurement, the larger the electric double layer charge / discharge current i dl Electric double layer capacitance C dl Therefore, the temperature change amount ΔT at which the estimation accuracy falls within an acceptable range is set as the third threshold, and deterioration diagnosis is performed only when the actual temperature change amount ΔT is equal to or less than the third threshold. In other words, the third threshold is the temperature change amount at which the estimation accuracy of the electric double layer capacitance Cdl falls within an acceptable range. The specific value is the electric double layer charge / discharge current idl The influence of the temperature change amount ΔT on the estimation of is obtained by experiment or the like, and is set arbitrarily within a range in which the estimation accuracy is within an allowable range.

[0048] In step S107, the controller 2 determines whether the actual potential sweep rate v is equal to or less than the first threshold value. If it is equal to or less than the first threshold value, the controller 2 executes the process of step S108. If it is greater than the first threshold value, the controller 2 ends this routine.

[0049] This step is the electric double layer capacitance C dl The potential sweep rate v for deterioration diagnosis is set in advance, but the actual potential sweep rate v does not necessarily match the setting. As mentioned above, if the potential sweep rate is too fast, the calculated electric double layer capacitance C dl Therefore, the actual potential sweep rate v is calculated based on the measured cell voltage E, and deterioration diagnosis is performed only when the value is equal to or less than the first threshold value. In other words, the first threshold value is the electric double layer capacitance C estimated by the above method. dl is the potential sweep rate v, which indicates the capacity of the entire electrode. The specific value varies depending on the composition, structure, etc. of the power generating element 10, so it is necessary to determine the electric double layer capacity C of the entire electrode by experiment, etc. dl The potential sweep rate v at which the potential sweep rate satisfies the above equation is calculated and set as the first threshold value.

[0050] In step S108, the controller 2 determines whether the fluctuation amount dv / dt per unit time of the potential sweep rate v is equal to or less than a second threshold value set in advance. If it is equal to or less than the second threshold value, the controller 2 executes the process of step S109. If it is greater than the second threshold value, the controller 2 ends this routine. dl This is to determine whether it is possible to estimate with accuracy.

[0051] In Figure 4, the fluctuations in cell voltage E in each of the charge and discharge sections are shown as straight lines, but this shows the ideal change (i.e., the change at the set potential sweep rate v). As mentioned above, the actual potential sweep rate v does not follow the set rate, but rather undergoes repeated small fluctuations around the set value. Since fluctuations in cell voltage E affect current i, the larger the fluctuation amount per unit time dv / dt of the potential sweep rate v, the larger the fluctuation in current i will be. Furthermore, if current i fluctuates significantly, the electric double layer charge / discharge current i dl The accuracy of the estimation of the electric double layer capacitance C dl Therefore, the change per unit time dv / dt of the actual potential sweep rate v is calculated based on the measured cell voltage E, and deterioration diagnosis is performed only when this value is equal to or less than the second threshold value. In other words, the second threshold value is the electric double layer charge / discharge current i dl The value of the change per unit time dv / dt of the potential sweep rate v at which the estimation accuracy of is within an allowable range. The specific value differs depending on the composition, structure, etc. of the power generating element 10, and is therefore set based on experiments, etc.

[0052] In step S109, the controller 2 calculates the electric double layer capacitance C dl The calculation method is as described above.

[0053] In step S110, the controller 2 determines whether the effective interfacial area has decreased from the effective interfacial area in the normal state of the SOC recorded in step S102. If it has decreased, the controller 2 executes the process of step S111. If it has not decreased, the controller 2 ends this routine. The determination in this step is to determine whether it is necessary to increase the cell pressure.

[0054] As mentioned above, the effective interfacial area and the electric double layer capacitance Cdl There is a correlation between the electric double layer capacitance Cdl and the effective interfacial area, and it can be estimated that the larger the electric double layer capacitance Cdl, the larger the effective interfacial area. Therefore, in this step, this relationship is used to calculate the electric double layer capacitance C calculated in step S109. dl and the normal electric double layer capacitance C at the first recorded SOC. dlThe fifth threshold is used to determine whether the effective interfacial area has decreased. dl is calculated in advance by performing the same processing as S103 to S109 for each SOC of a secondary battery that has the same structure as the secondary battery 1 to be diagnosed and is known to be normal, and is stored in the controller 2.

[0055] As described above, in this embodiment, the fifth threshold value used to determine whether to increase the cell pressurizing force is changed depending on the SOC for the following reasons.

[0056] It is known that the volume of the electrode active material expands and contracts during charging and discharging (see Figure 7). Figure 7 shows the relationship between charging and discharging and the expansion and contraction of the volume when the electrode is LCO and when it is NMC. For example, when the electrode is NMC, even if normal, the higher the SOC, the greater the electric double layer capacity C due to the contraction of the active material. dl (See Figure 8). In other words, the higher the SOC, the smaller the effective interfacial area. Figure 8 shows the relationship between SOC and electric double layer capacitance C dl FIG.

[0057] The decrease in effective interfacial area due to the contraction of the active material is a reversible change and not deterioration. Therefore, comparing a normal state in which the effective interfacial area is decreased due to contraction of the active material with the effective interfacial area in a state in which the active material is not contracted does not allow for accurate diagnosis of deterioration. In other words, by changing the fifth threshold value according to the SOC, the decrease in effective interfacial area due to deterioration can be accurately determined.

[0058] In step S111, when increasing the cell pressure, the controller 2 sets the cell pressure after the increase. Here, the rate of increase of the cell pressure is increased as the degree of decrease in the effective interfacial area increases. The degree of decrease can be expressed by various parameters. For example, the electric double layer capacitance C in a normal state is dl Current electric double layer capacitance C dl The ratio of the electric double layer capacity in normal condition, Cdl The normal state electric double layer capacitance C dl and the current electric double layer capacitance C dl The difference ratio between the normal electric double layer capacitance and the normal electric double layer capacitance, C dl and the current electric double layer capacitance C dl The difference between the two may be any of the above.

[0059] In step S112, the cell is pressurized with the cell pressure set in step S111. If the pressurizing mechanism 20 has the configuration shown in Fig. 2, the operator manually adjusts the cell pressure. On the other hand, if the controller 2 is configured to adjust the cell pressure by operating an actuator or the like, the controller 2 changes the cell pressure to the value set in step S111.

[0060] In order to perform the above control routine, a diagnostic device capable of CV measurement may be installed in the vehicle, or data on voltage and current when switching from power running to regeneration or from regeneration to power running during operation may be utilized.

[0061] As described above, this embodiment provides a battery deterioration diagnosis method for determining whether or not it is necessary to change the cell pressure applied by the pressure mechanism 20, which applies a cell pressure (pressure) from the stacking direction to the battery stack 11 including a plurality of stacked power generating elements 10. In this method, the controller 2 calculates the electric double layer capacitance C based on the amount of change in the current value i when the voltage E changes due to switching between charging and discharging of the power generating elements 10. dl Calculate the electric double layer capacitance C dl Based on this, the increase or decrease in the effective interfacial area relative to the normal state is estimated, and if it is estimated that the effective interfacial area has decreased, it is determined that the cell pressure (applied pressure) needs to be increased, and if it is estimated that it has not decreased, it is determined that there is no need to change the cell pressure. dlSince there is a correlation between the effective interfacial area and the cell pressure, this embodiment can accurately estimate whether the effective interfacial area is decreasing and, based on this, determine whether it is necessary to change the cell pressure. As a result, if the effective interfacial area is not decreasing, the cell pressure will not be increased, thereby suppressing the extrusion of electrode material due to creep and the formation of dendrites, which can cause short circuits. When diagnosing the deterioration of a secondary battery 1 based on AC impedance, it generally takes about 5 to 15 minutes to measure the electrode reaction resistance on the low-frequency side. In contrast, this embodiment can estimate the decrease in effective interfacial area using only information about the halfway point of charge / discharge, so it only takes about 20 seconds.

[0062] In this embodiment, the controller 2 controls the electric double layer capacitance C dl The calculation of the electric double layer capacitance C is performed only when the potential sweep rate v is equal to or less than a first threshold value set in advance. dl Since the deterioration diagnosis is performed only when it is possible to estimate the deterioration, it is possible to appropriately determine whether or not to increase the cell pressurizing force.

[0063] In this embodiment, the controller 2 controls the electric double layer capacitance C dl The calculation of the electric double layer capacitance C is performed only when the fluctuation amount per unit time of the potential sweep rate v is equal to or less than a second threshold value set in advance. dl Since the deterioration diagnosis is performed only when it is possible to estimate the deterioration, it is possible to appropriately determine whether or not to increase the cell pressurizing force.

[0064] In this embodiment, the controller 2 controls the electric double layer capacitance C dl The calculation of the electric double layer capacitance C is performed only when the change in the battery temperature T per unit time is equal to or less than a third threshold value set in advance. dl Since the deterioration diagnosis is performed only when it is possible to estimate the deterioration, it is possible to appropriately determine whether or not to increase the cell pressurizing force.

[0065] In this embodiment, the controller 2 controls the electric double layer capacitance C dlis calculated only when the temperature distribution in the cell surface of the battery stack 11 is equal to or less than a fourth threshold value set in advance. dl Since the deterioration diagnosis is performed only when it is possible to estimate the deterioration, it is possible to appropriately determine whether or not to increase the cell pressurizing force.

[0066] In this embodiment, the controller 2 controls the electric double layer capacitance C dl The fifth threshold value used to determine whether the effective interfacial area has decreased is changed according to the actual SOC (charge rate) at the start of the calculation. This makes it possible to appropriately determine whether to increase the cell pressure even if the effective interfacial area has decreased due to contraction of the active material accompanying a change in SOC.

[0067] In this embodiment, the controller 2 sets a larger value as the increased cell pressure as the degree of reduction in the effective interfacial area increases. This results in an appropriate cell pressure according to the degree of reduction in the effective interfacial area, improving the contact state between the electrolyte and the electrodes and reducing the risk of short circuiting caused by applying an unnecessarily large cell pressure.

[0068] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments. [Explanation of symbols]

[0069] 1 secondary battery, 2 controller, 3 temperature sensor, 4 current sensor, 5 voltage sensor, 10 power generation element, 11 battery stack, 20 pressure mechanism, 100 battery control system

Claims

1. 1. A battery deterioration diagnosis method for determining whether or not a cell pressure force of a pressure mechanism that applies a cell pressure force in a stacking direction to a battery stack including a plurality of stacked power-generating elements needs to be changed, The controller calculating an electric double layer capacity based on a change in current value during a voltage change accompanying switching between charging and discharging of the power generating element; Estimating an increase or decrease in the effective interfacial area relative to a normal state based on the electric double layer capacitance; A battery deterioration diagnosis method characterized by determining that the cell pressure needs to be increased when it is estimated that the effective interfacial area has decreased, and determining that the cell pressure does not need to be changed when it is estimated that the effective interfacial area has not decreased.

2. 2. The battery deterioration diagnosis method according to claim 1, The controller calculates the electric double layer capacity only when a potential sweep rate is equal to or lower than a preset first threshold.

3. 3. The battery deterioration diagnosis method according to claim 2, The controller calculates the electric double layer capacity only when the amount of change per unit time of the potential sweep rate is equal to or less than a second threshold value set in advance.

4. 2. The battery deterioration diagnosis method according to claim 1, The controller calculates the electric double layer capacity only when a change in battery temperature per unit time is equal to or less than a preset third threshold.

5. 5. The battery deterioration diagnosis method according to claim 4, The battery deterioration diagnosis method, wherein the controller calculates the electric double layer capacity only when a temperature distribution within a cell surface of the battery stack is equal to or less than a fourth threshold value set in advance.

6. 2. The battery deterioration diagnosis method according to claim 1, The controller changes a fifth threshold value used to determine whether the effective interfacial area has decreased, depending on an actual charging rate at the start of calculation of the electric double layer capacity.

7. 2. The battery deterioration diagnosis method according to claim 1, The method for diagnosing battery degradation, wherein the controller sets a larger value as the increased cell pressing force as the degree of decrease in the effective interfacial area increases.

8. 1. A battery deterioration diagnosis device for determining whether or not a cell pressure force of a pressure mechanism that applies a cell pressure force in a stacking direction to a battery stack including a plurality of stacked power-generating elements needs to be changed, an electric double layer capacity calculation unit that calculates an electric double layer capacity based on a change in current value when a voltage changes due to switching between charging and discharging of the power generating element; an increase / decrease estimation unit that estimates an increase / decrease in the effective interfacial area relative to a normal state based on the electric double layer capacitance; a deterioration diagnosis unit that determines that the cell pressurizing force needs to be increased when it is estimated that the effective interfacial area has decreased, and that the cell pressurizing force does not need to be changed when it is estimated that the effective interfacial area has not decreased; A battery deterioration diagnosis device comprising:

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