Battery sorting method and battery sorting device

Abstract

To provide a battery sorting method and a battery sorting device capable of quickly sorting a used secondary battery into a secondary battery requiring chemical treatment and a secondary battery not requiring chemical treatment when reusing the used secondary battery.SOLUTION: There is provided a battery sorting method for sorting a secondary battery including a battery stack in which a plurality of power generation elements is stacked. The battery sorting method includes: calculating, with respect to the used secondary battery, an electric double layer capacity based on a change amount of a current value at a time of voltage change accompanying charge / discharge switching of the power generating element; and estimating, based on the electric double layer capacity, magnitude of effective interface area with respect to a normal state. Then, based on an estimation result, the secondary batteries are sorted into a secondary battery requiring chemical treatment and a secondary battery not requiring chemical treatment when reusing the used secondary battery.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a battery sorting method and a battery sorting device. [Background technology]

[0002] When reusing used secondary batteries, chemical treatment is required if the electrode material is chemically deteriorated, for example, if the ratio of lithium to transition metals (hereinafter referred to as the Li / Me ratio) has changed or if transition metals such as cobalt and manganese have eluted. On the other hand, if the electrode structure has deteriorated rather than the electrode material, such as when the interface between the active material and the electrolyte has peeled off, the battery can be reused without chemical treatment. Therefore, when reusing used secondary batteries, they must be sorted according to their state of deterioration.

[0003] As a method for diagnosing the degradation state of a secondary battery, Patent Document 1 discloses a method for diagnosing the degradation state of a secondary battery using AC impedance measured by an AC impedance method as a parameter. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 255557 Summary of the Invention [Problem to be solved by the invention]

[0005] However, AC impedance is the sum of the resistances of the positive and negative electrodes, and is affected by a combination of factors, such as the area of ​​the interface between the electrolyte and electrodes of a secondary battery (hereinafter also referred to as the effective interfacial area) and chemical degradation of the electrode material. Therefore, the diagnostic method described in Patent Document 1 cannot determine whether the deterioration of a secondary battery is due to chemical degradation of the electrode material or to degradation of the electrode structure. Furthermore, because it takes time to measure AC impedance, it is not possible to quickly determine the state of deterioration. In other words, it is difficult to use the diagnostic method described in Patent Document 1 to sort secondary batteries when they are reused.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a battery sorting method and a battery sorting device that can quickly sort used secondary batteries into those that require chemical treatment and those that do not when they are reused. [Means for solving the problem]

[0007] According to one aspect of the present invention, there is provided a battery sorting method for sorting secondary batteries including a battery stack in which multiple power generating elements are stacked. This battery sorting method calculates the electric double layer capacity of used secondary batteries based on the amount of change in current value during voltage changes associated with switching between charging and discharging of the power generating elements, and estimates the effective interfacial area relative to the normal state based on the electric double layer capacity. Then, based on the estimation results, the secondary batteries are sorted into those that require chemical treatment for reuse and those that do not. [Effects of the Invention]

[0008] According to the present invention, the electric double layer capacity of a used secondary battery is calculated, and the effective interfacial area relative to the normal state is estimated based on the electric double layer capacity. This makes it possible to quickly determine whether deterioration of the secondary battery is due to chemical deterioration of the electrode material or deterioration of the electrode structure. Therefore, secondary batteries that require chemical treatment for reuse can be quickly sorted from unnecessary secondary batteries. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of a battery sorting 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 illustrating the battery sorting method according to this embodiment. [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

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] 1 is a schematic diagram of a battery control system 100 to which a battery sorting method according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram of a secondary battery 1 included in the battery control system 100.

[0012] The battery control system 100 includes a secondary battery 1 and a battery controller (hereinafter also simply referred to as "controller") 2, and can be mounted on, for example, an automobile or the like, but is not limited to this.

[0013] The secondary battery 1 is, for example, a known lithium deposition type all-solid-state battery. The secondary battery 1 includes a stack (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 stack 11 in the stacking direction.

[0014] The pressure mechanism 20 includes an upper end plate 12 that contacts the power generation element 10 at the upper end of the stack 11, a lower end plate 13 that contacts the power generation element 10 at the lower end of the 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.

[0015] 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.

[0016] 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 SOC (State of Charge) management and charge / discharge control, as well as sorting judgments for used secondary batteries, which will be described later. In other words, the controller 2 functions as a battery sorting device that sorts used secondary batteries. The controller 2 is composed of a microcomputer equipped with a central processing unit (CPU), read-only memory (ROM), random access memory (RAM), and input / output interface (I / O interface). The controller 2 can also be composed of multiple microcomputers.

[0017] For sorting judgment, the controller 2 includes a first judgment unit 21 and a second judgment unit 22. The first judgment unit 21 judges the electric double layer capacitance (C dl) calculation unit 21A, an increase / decrease estimation unit 21B that estimates an increase / decrease in the effective interfacial area, and a sorting determination unit 21C that determines the degradation state of the used secondary battery 1 based on the increase / decrease in the effective interfacial area and decides where to sort it. The second determination unit 22 also includes a pressure setting unit 22A that sets the cell pressure of the secondary battery 1, and a second electric double layer capacity (C dl ) calculation unit 22B that estimates an increase or decrease in the effective interfacial area, a second increase or decrease estimation unit 22C that estimates an increase or decrease in the effective interfacial area, and a second sorting judgment unit 22D that judges the deterioration state of the used secondary battery 1 based on the increase or decrease in the effective interfacial area and determines the sorting destination.

[0018] The deterioration state of the used secondary battery 1 that is the subject of the above-mentioned sorting judgment will be described with reference to FIG.

[0019] FIG. 3 is a schematic diagram of an electrode having a three-dimensional structure (hereinafter also referred to as a three-dimensional electrode), in which (a) shows a normal state, and (b) and (c) show deteriorated states.

[0020] Secondary battery degradation can be attributed to chemical degradation of the electrode material or degradation of the electrode structure. Figure 3(b) shows a state in which the electrode material has chemically deteriorated, with some of the active material altered. On the other hand, Figure 3(c) shows a state in which the electrode structure has deteriorated, with a reduced effective interfacial area between the electrolyte and active material. The reduction in effective interfacial area occurs when the electrolyte and active material, which are normally in close contact, become at least partially separated as shown in regions A and B in Figure 3(c) after repeated charge and discharge. Even if such separation occurs, applying pressure to the cell can restore the effective interfacial area by reconnecting the separated active material and electrolyte. That is, when the electrode structure has deteriorated, such as when the interface between the active material and electrolyte has separated, a used secondary battery can be reused (reused in a vehicle) or repurposed (reused in a vehicle or for a non-vehicle purpose) by simply applying pressure to the cell without chemical treatment. On the other hand, when the electrode material has chemically deteriorated, chemical treatment is required for reuse. Therefore, when used secondary batteries are to be reused, they must be sorted according to their state of deterioration.

[0021] Here, a known method for diagnosing the degradation state of a secondary battery is to diagnose the degradation state of the secondary battery using, for example, AC impedance measured by an AC impedance method as a parameter. However, AC impedance is the sum of the resistances of the positive and negative electrodes, and is affected by a combination of factors such as the area of ​​the interface between the electrolyte and the electrode of the secondary battery (effective interfacial area) and chemical degradation of the electrode material. Therefore, a diagnosis method using the AC impedance method cannot determine whether the degradation of the secondary battery is due to chemical degradation of the electrode material or degradation of the electrode structure. Furthermore, because it takes time to measure AC impedance, it is difficult to quickly determine the degradation state.

[0022] Therefore, in this embodiment, the electric double layer capacity C dl Calculate the electric double layer capacitance C dl Based on this, the size of the effective interfacial area relative to the normal state is estimated, and the used secondary batteries 1 are sorted based on the estimation result. dl By estimating the effective interfacial area based on this, it is possible to determine whether the deterioration of the secondary battery is due to chemical deterioration of the electrode material or deterioration of the electrode structure. In addition, compared to measurements such as AC impedance, the electric double layer capacitance C dl Therefore, secondary batteries that require chemical treatment when reused (hereinafter also referred to as recycled secondary batteries) can be quickly separated from unnecessary secondary batteries (hereinafter also referred to as reusable or repurposeable secondary batteries).

[0023] The battery sorting method according to this embodiment will be described in detail below. The secondary batteries 1 to be sorted are assumed to be used secondary batteries that are in a deteriorated state, such as having a lower capacity or an increased resistance compared to a normal state.

[0024] Controller 2, more specifically, C dl The calculation unit 21A switches between charging and discharging at a predetermined potential sweep rate, and calculates the electric double layer capacitance C based on the amount of change in the current value when the voltage changes due to the switching between charging and discharging.dl This will be explained with reference to FIGS.

[0025] 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.

[0026] 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.

[0027]

number

[0028] 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.

[0029]

number

[0030] On the other hand, the electric double layer charge / discharge current i dl is proportional to the potential sweep rate v (Equation (3)).

[0031]

number

[0032] As shown in equation (3), in the case of a three-dimensional electrode, the electric double layer capacitance C dl 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 is considered to represent the capacitance of the entire electrode layer. In this embodiment, the capacitance of the entire electrode layer is used to determine the deterioration state.

[0033] 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.

[0034] C dl The calculation unit 21A calculates the electric double layer charge / discharge current i dl From equation (3), the electric double layer capacitance C dl Calculate.

[0035] FIG. 5 shows the electric double layer capacity C dl The vertical axis shows the electric double layer capacitance C dl The 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.

[0036] 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.

[0037] 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.

[0038] 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 21B estimates the increase / decrease in the effective interfacial area by this method.

[0039] Then, based on the estimation results of the increase / decrease estimation unit 21B, the sorting judgment unit 21C determines whether the deterioration of the secondary battery 1 is due to chemical deterioration of the electrode material, and if it is due to chemical deterioration of the electrode material, sorts the secondary battery 1 as a secondary battery that requires chemical treatment when reused (a secondary battery to be recycled).

[0040] Specifically, if the increase / decrease estimation unit 21B estimates that the effective interfacial area has not decreased, the sorting determination unit 21C determines that the deterioration of the secondary battery 1 is due to chemical deterioration of the electrode material and that the secondary battery requires chemical treatment before reuse. That is, if the secondary battery 1 is in a deteriorated state, such as having a lower capacity or an increased resistance compared to a normal state, but the effective interfacial area has not decreased, there is a high possibility that chemical deterioration of the electrode material has occurred. Therefore, in this case, the secondary battery is determined to require chemical treatment before reuse (a secondary battery to be recycled).

[0041] On the other hand, if it is estimated that the effective interfacial area has decreased, it is possible that the deterioration of the secondary battery 1 has occurred due to separation of the electrolyte and the active material caused by charging and discharging. In this case, the pressure setting unit 22A of the second determination unit 22 sets the increased cell pressure in order to increase the cell pressure. Here, the pressure setting unit 22A increases the rate of increase of the cell pressure as the degree of decrease in the effective interfacial area relative to the normal state increases. The degree of decrease can be expressed by various parameters. For example, the electric double layer capacity C in the normal state dl Current electric double layer capacitance C dl The ratio of the electric double layer capacity in normal condition, C dl 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 increase in the pressure may be a difference between the pressure applied to the cell and the pressure applied to the cell. If the pressure mechanism 20 has the configuration shown in Fig. 2, the operator can manually adjust the pressure applied to the cell. On the other hand, if the controller 2 is configured to be able to adjust the pressure applied to the cell by operating an actuator or the like, the controller 2 changes the pressure applied to the cell to the value set by the pressure setting unit 22A.

[0042] When the cell pressure is increased, the second dl The calculation unit 22B calculates C dl Using the same method as that of the calculation unit 21A, the electric double layer capacitance C after the cell pressure increase dlFurther, the second increase / decrease estimation unit 22C estimates an increase / decrease in the effective interfacial area using the same method as the increase / decrease estimation unit 21B.

[0043] Based on the results of the estimation by the second increase / decrease estimation unit 22C, the second sorting judgment unit 22D determines whether the deterioration of the secondary battery 1 is due to chemical deterioration of the electrode material or deterioration of the electrode structure, and sorts the secondary batteries into those that require chemical treatment etc. when reused (secondary batteries that can be recycled) and those that are not needed (secondary batteries that can be reused or repurposed).

[0044] Specifically, if the second increase / decrease estimation unit 22C estimates that the effective interfacial area has improved to a normal state, the second sorting determination unit 22D determines that the deterioration of the secondary battery 1 is due to deterioration of the electrode structure and that the secondary battery does not require chemical treatment for reuse. In other words, if the effective interfacial area is restored when the cell pressure is increased, it is believed that the deterioration of the secondary battery 1 is caused by peeling between the electrolyte and the active material. Therefore, by increasing the cell pressure and improving adhesion to restore the performance of the secondary battery 1, the used secondary battery 1 can be reused or repurposed as is.

[0045] On the other hand, if the second increase / decrease estimation unit 22C estimates that the effective interfacial area has not improved, the second sorting judgment unit 22D determines that the deterioration of the secondary battery 1 is not due to deterioration of the electrode structure and judges that the secondary battery requires chemical treatment or the like when reused (a secondary battery to be recycled). In other words, if the effective interfacial area does not improve even when the cell pressure is increased, that is, if the performance of the secondary battery 1 cannot be restored even when the cell pressure is increased, the used secondary battery 1 cannot be reused or repurposed as is. Therefore, in this case, the used secondary battery 1 is sorted as a secondary battery requiring chemical treatment or the like.

[0046] 6 is a flowchart illustrating the battery sorting method according to this embodiment, showing an example of a control routine for operations according to the results of determining the degradation state of used secondary batteries 1. The following will explain the steps.

[0047] In step S100, the controller 2 determines whether the temperature distribution (difference between high temperature and low temperature areas) within the cell surface of the battery stack 11 is equal to or less than a fourth threshold value set in advance, and if it is equal to or less than the fourth threshold value, the process of step S101 is executed. On the other hand, if it is greater than the fourth threshold value, this routine is terminated, and after a predetermined time has elapsed, the controller 2 executes the process of step S100 again. This step is for determining whether the state of deterioration can be accurately determined. 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, 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 When it is not possible to estimate the temperature distribution in the cell plane (when the temperature distribution in the cell plane is equal to or lower than the fourth threshold), it is decided not to judge the deterioration state.

[0048] 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.

[0049] In step S101, the controller 2 determines whether the secondary battery 1 is in a state where it can be charged or discharged, and if it is, executes the process of step S102. On the other hand, if it is not possible to charge or discharge, this routine ends and, after a predetermined time has elapsed, executes the process of step S100 again. This step is for determining whether switching between charging and discharging to determine the degradation state 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 an attempt is made to determine the degradation state 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, if the SOC (state of charge) of the secondary battery 1 is within a range where the above restriction does not apply even when switching between charging and discharging to determine the degradation state, it is determined that charging and discharging are possible, but if it is outside this range, it is determined that charging and discharging are not possible.

[0050] 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).

[0051] In step S103, the controller 2 starts measuring the temperature (battery temperature) T, cell voltage E, and current i of the secondary battery 1, and also starts measuring the time t from the start of the measurements.

[0052] In step S104, the controller 2 determines whether a predetermined time has elapsed since the switching of charging and discharging. If the predetermined time has elapsed, the controller 2 executes the process of step S105. If the predetermined time has not elapsed, the controller 2 repeats the processes of steps S103 and S104 until the predetermined time has elapsed. The predetermined time here is determined based on the electric double layer charging and discharging 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.

[0053] In step S105, the controller 2 ends the measurement of each value that began in step S103.

[0054] In step S106, the controller 2 determines whether the change amount ΔT of the battery temperature T being measured (hereinafter also referred to as the temperature change amount) is equal to or less than the third threshold, and if it is equal to or less than the third threshold, executes the process of step S107. On the other hand, if it is greater than the third threshold, this routine ends, and after a predetermined time has elapsed, executes the process of step S100 again. 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 the deterioration state is judged 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 i dl 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.

[0055] In step S107, the controller 2 determines whether the actual potential sweep rate v is equal to or less than the first threshold, and if it is equal to or less than the first threshold, executes the process of step S108. On the other hand, if it is greater than the first threshold, the controller 2 ends this routine and executes the process of step S100 again after a predetermined time has elapsed.

[0056] This step is the electric double layer capacitance C dl The potential sweep rate v for determining the degradation state is preset, but the actual potential sweep rate v does not necessarily match the preset rate. 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. dlis 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.

[0057] 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, and if it is equal to or less than the second threshold value, executes the process of step S109. On the other hand, if it is greater than the second threshold value, the routine ends, and after a predetermined time has elapsed, the process of step S100 is executed again. In this step, the electric double layer capacitance C dl This is to determine whether it is possible to estimate with accuracy.

[0058] 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 repeats small fluctuations around the set value. Since fluctuations in cell voltage E affect current i, the larger the fluctuation amount per time dv / dt of the potential sweep rate v, the larger the fluctuation in current i. Furthermore, when current i fluctuates greatly, 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 the degradation state is judged only when the 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.

[0059] In step S109, the controller 2 calculates the electric double layer capacitance C dl The calculation method is as described above.

[0060] In step S110, the controller 2 determines whether the effective interfacial area has decreased from the effective interfacial area in the normal state at the SOC recorded in step S102. As described above, the effective interfacial area and the electric double layer capacitance C dl There is a correlation between the electric double layer capacitance C dl It can be estimated that the larger the effective interfacial area, 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. dl The 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 whose degradation state is to be determined and is known to be normal, and is stored in the controller 2.

[0061] As described above, in this embodiment, the fifth threshold value used to determine whether the effective interfacial area has decreased with respect to the normal state is changed depending on the SOC. The reason for this is as follows.

[0062] 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 contraction of the active material, which reduces the electric double layer capacity C. 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.

[0063] 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.

[0064] The determination of whether the effective interfacial area has decreased is based on the electric double layer capacitance C dl The calculation is performed at two points, the first SOC and the second SOC, where the actual SOC is different, and the electric double layer capacitance C dl The ratio may be compared with the ratio in a normal state (sixth threshold value). That is, for the used secondary battery 1, the electric double layer capacity C dl The ratio of the electric double layer capacitance C dl For example, as mentioned above, when the electrode is NMC, even if it is normal, the higher the SOC, the smaller the electric double layer capacity C due to the contraction of the active material. dl becomes smaller, but the electric double layer capacitance C dl By comparing the ratio of the effective interfacial area and the effective interfacial area, it is possible to check whether the effective interfacial area is behaving normally. Therefore, it is possible to more accurately determine whether the effective interfacial area has decreased due to deterioration.

[0065] In step S110, if the effective interfacial area of ​​the secondary battery 1 is not reduced compared to its normal state, the controller 2 determines that the deterioration of the secondary battery 1 is due to chemical degradation of the electrode material, and in step S116, sorts the secondary battery as one that requires chemical treatment before reuse (a secondary battery to be recycled). As described above, if the effective interfacial area of ​​the secondary battery 1 is not reduced despite being in a deteriorated state, there is a high possibility that chemical degradation of the electrode material has occurred. Therefore, if the effective interfacial area of ​​the secondary battery 1 is not reduced compared to its normal state, it is sorted as a secondary battery that requires chemical treatment before reuse. Note that the sorting of the secondary batteries 1 may be performed mechanically, such as by a conveyor system, or manually by an operator.

[0066] On the other hand, in step S110, if the effective interfacial area of ​​the secondary battery 1 is reduced compared to the normal state, the controller 2 determines that the deterioration of the secondary battery 1 is caused by peeling of the electrolyte and active material due to charging and discharging, and executes the processing of step S111.

[0067] Steps S111 and S112 are steps for increasing the cell pressure. In step S111, the controller 2 sets the cell pressure after the increase when increasing the cell pressure. Here, the rate of increase of the cell pressure increases as the degree of decrease in the effective interfacial area increases. As described above, the degree of decrease is determined by the electric double layer capacitance C dl Current electric double layer capacitance C dl This can be expressed by various parameters, such as the ratio of the effective interfacial area to the cell pressure. In this way, the increase rate of the cell pressure is determined according to the degree of reduction in the effective interfacial area, so the cell pressure is not increased more than necessary. Therefore, for reused secondary batteries 1, protrusion of electrode material due to creep and the generation of dendrites, which can cause short circuits, can be suppressed. In addition, unnecessary control can be reduced, improving sorting efficiency.

[0068] In step S112, the cell is pressurized with the cell pressure set in step S111. As described above, the cell pressure can be adjusted manually by an operator or by the controller 2 operating an actuator or the like.

[0069] In step S112, when the cell pressure is changed, in step S113, the controller 2 calculates the electric double layer capacitance C dl That is, the processes of steps S100 to S109 are performed again.

[0070] In step S114, the controller 2 determines whether the effective interfacial area has been improved to a normal state by measuring the electric double layer capacitance C dl If the effective interfacial area has improved to a normal state, the controller 2 determines that the deterioration of the secondary battery 1 is due to deterioration of the electrode structure, and in step S115 classifies the secondary battery as one that does not require chemical treatment when reused. A secondary battery 1 that has been classified as one that does not require chemical treatment when reused can be reused or repurposed as is.

[0071] On the other hand, if the effective interfacial area has not improved to a normal state, the secondary battery 1 cannot be reused or repurposed. Therefore, the controller 2 determines that the deterioration of the secondary battery 1 is not due solely to deterioration of the electrode structure, and in step S116, sorts the secondary battery 1 as a secondary battery that requires chemical treatment or the like before reuse (a secondary battery to be recycled). As mentioned above, sorting of the secondary batteries 1 may be performed mechanically, such as by a conveyor system, or manually by a worker.

[0072] As described above, in this embodiment, the electric double layer capacity C dl Calculate the electric double layer capacitance C dlBased on this, it is determined whether the effective interfacial area has decreased compared to the normal state. If it has not decreased, it is classified as a secondary battery that requires chemical treatment when reused (a secondary battery that can be recycled). On the other hand, if the effective interfacial area of ​​the used secondary battery 1 has decreased compared to the normal state, the cell pressure is increased to restore the effective interfacial area, and the secondary battery is classified as a secondary battery that does not require chemical treatment (a secondary battery that can be reused or repurposed). In this way, the electric double layer capacity C dl By estimating the effective interfacial area based on this, it is possible to determine whether the deterioration of the secondary battery is due to chemical deterioration of the electrode material or deterioration of the electrode structure. In addition, compared to measurements such as AC impedance, the electric double layer capacitance C dl This calculation can be performed in a short time. Therefore, it is possible to quickly separate secondary batteries that require chemical treatment when reused (secondary batteries to be recycled) from unnecessary secondary batteries (secondary batteries that can be reused or repurposed).

[0073] According to the battery sorting method of the above embodiment, the following effects can be obtained.

[0074] According to the battery sorting method of this embodiment, the electric double layer capacity C dl Calculate the electric double layer capacitance C dl Based on this, the size of the effective interfacial area relative to the normal state is estimated. This makes it possible to determine whether the deterioration of the secondary battery is due to chemical deterioration of the electrode material or deterioration of the electrode structure. In addition, compared to measurements such as AC impedance, the electric double layer capacitance C dl Therefore, secondary batteries that require chemical treatment when reused can be quickly separated from unnecessary secondary batteries.

[0075] According to the battery sorting method of this embodiment, when the effective interfacial area of ​​a used secondary battery 1 is reduced compared to its normal state, the secondary battery 1 is pressurized in the stacking direction of the power generating element 10, and the size of the effective interfacial area of ​​the pressurized secondary battery compared to its normal state is estimated. Then, based on the estimation result, the secondary batteries are sorted into those that require chemical treatment when reused and those that do not. In this way, by pressurizing the secondary batteries 1 whose effective interfacial area is reduced compared to its normal state and then estimating the size of the effective interfacial area compared to its normal state, secondary batteries 1 that can be reused or repurposed as they are can be more appropriately sorted when reused.

[0076] According to the battery sorting method of this embodiment, if the effective interfacial area of ​​a used secondary battery 1 is reduced compared to a normal state, the secondary battery 1 is pressurized in the stacking direction of the power generating element 10 with a pressure that increases with the degree of reduction in the effective interfacial area. By determining the rate of increase in the cell pressurizing force according to the degree of reduction in the effective interfacial area, it is possible to prevent unnecessary increases in the cell pressurizing force. Therefore, for reused secondary batteries 1, problems such as electrode material protrusion and dendrite formation due to creep, which can cause short circuits, can be suppressed. Furthermore, unnecessary control can be reduced, improving sorting efficiency.

[0077] According to the battery sorting method of this embodiment, the electric double layer capacity C dl is calculated only when the potential sweep rate v is equal to or less than a first threshold value set in advance. dl Since the state of deterioration is determined only when it is possible to estimate the deterioration state, it is possible to more appropriately determine which secondary batteries require chemical treatment when reused and which do not.

[0078] According to the battery sorting method of this embodiment, the electric double layer capacity C dl is calculated 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. dlSince the state of deterioration is determined only when it is possible to estimate the deterioration state, it is possible to more appropriately determine which secondary batteries require chemical treatment when reused and which do not.

[0079] According to the battery sorting method of this embodiment, the electric double layer capacity C dl is calculated 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 state of deterioration is determined only when it is possible to estimate the deterioration state, it is possible to more appropriately determine which secondary batteries require chemical treatment when reused and which do not.

[0080] According to the battery sorting method of this embodiment, the electric double layer capacity C dl is 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 state of deterioration is determined only when it is possible to estimate the deterioration state, it is possible to more appropriately determine which secondary batteries require chemical treatment when reused and which do not.

[0081] According to the battery sorting method of this embodiment, the electric double layer capacity C dl The fifth threshold used to determine whether the effective interfacial area has decreased is changed according to the actual SOC (charge rate) at the start of calculation. This makes it possible to more appropriately determine which secondary batteries require chemical treatment when reused and which do not, even if the effective interfacial area decreases due to contraction of the active material accompanying a change in SOC.

[0082] In this embodiment, when the effective interfacial area of ​​a used secondary battery 1 is reduced compared to its normal state, it is preferable to pressurize (increase the pressure) the secondary battery 1, estimate the size of the effective interfacial area of ​​the pressurized (increased) secondary battery compared to its normal state, and, based on the estimation result, sort the secondary battery into those that require chemical treatment when reused and those that do not require chemical treatment. However, this is not necessarily limited to this. For example, when it is estimated that the effective interfacial area of ​​a used secondary battery 1 is reduced compared to its normal state, it may be sorted as a secondary battery that does not require chemical treatment when reused. In other words, when the effective interfacial area is reduced compared to its normal state, it may be sorted as a secondary battery that does not require chemical treatment when reused without performing the processes of steps S111 to S114 in the flowchart of FIG. 6.

[0083] 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]

[0084] 1: Secondary battery, 2: Controller (battery sorting device), 3: Temperature sensor, 4: Current sensor, 5: Voltage sensor, 10: Power generation element, 11: Battery stack (laminated body), 20: Pressurizing mechanism, 100: Battery control system

Claims

1. A battery sorting method for sorting secondary batteries including a battery stack in which a plurality of power generating elements are stacked, comprising: calculating an electric double layer capacity of the used secondary battery based on a change in current value during a voltage change accompanying switching between charging and discharging of the power generating element; based on the electric double layer capacity, the size of the effective interfacial area relative to a normal state is estimated, and based on the estimation result, the secondary batteries are classified into those that require chemical treatment when reused and those that do not require chemical treatment. How to sort batteries.

2. 2. The battery sorting method according to claim 1, If the effective interfacial area is reduced compared to a normal state, a pressure is applied to the secondary battery from the stacking direction of the power generating element, the effective interfacial area of ​​the secondary batteries after pressurization is estimated relative to that of the normal state, and based on the estimation result, the secondary batteries are classified into those that require chemical treatment when reused and those that do not require chemical treatment; How to sort batteries.

3. 3. The battery sorting method according to claim 2, The pressing force during pressing is larger as the degree of reduction in the effective interfacial area is larger. How to sort batteries.

4. 3. The battery sorting method according to claim 1 or 2, The electric double layer capacitance is calculated only when the potential sweep rate is equal to or less than a predetermined first threshold value. How to sort batteries.

5. 5. The battery sorting method according to claim 4, The electric double layer capacitance is calculated only when the fluctuation amount per unit time of the potential sweep rate is equal to or less than a second threshold value set in advance. How to sort batteries.

6. 3. The battery sorting method according to claim 1 or 2, The electric double layer capacity is calculated only when the change in battery temperature per unit time is equal to or less than a third threshold value set in advance. How to sort batteries.

7. 7. The battery sorting method according to claim 6, The electric double layer capacity is calculated only when the temperature distribution in the cell surface of the battery stack is equal to or less than a fourth threshold value set in advance. How to sort batteries.

8. 3. The battery sorting method according to claim 1 or 2, a fifth threshold value used to determine whether the effective interfacial area is reduced compared to the effective interfacial area in a normal state is changed according to an actual charging rate at the start of calculation of the electric double layer capacity; How to sort batteries.

9. 9. The battery sorting method according to claim 8, The electric double layer capacity is calculated at two different actual charging rates. How to sort batteries.

10. A battery sorting device that sorts secondary batteries having a battery stack in which a plurality of power generating elements are stacked, an electric double layer capacity calculation unit that calculates an electric double layer capacity of the used secondary battery based on a change in current value during a voltage change accompanying switching between charging and discharging of the power generating element; an increase / decrease estimation unit that estimates the size of the effective interfacial area relative to a normal state based on the electric double layer capacitance; a sorting determination unit that sorts secondary batteries into those that require chemical treatment when reused and those that do not require chemical treatment based on the result of estimation by the increase / decrease estimation unit; Battery sorting device.

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