JP7529458B2 - Method and device for determining deterioration of lithium ion secondary battery - Google Patents

Description

The present invention relates to a method for determining the deterioration of a lithium ion secondary battery and a device for determining the deterioration of a lithium ion secondary battery.

Conventionally, as shown in, for example, Patent Document 1, a method is known in which the resistance and capacity of a collected secondary battery are measured, and the deterioration state of the secondary battery is determined based on these resistance and capacity. By adopting such a configuration, it is possible to easily determine whether the secondary battery can be used. Furthermore, modules with similar degrees of deterioration can be combined and packaged. This makes it possible to suppress variations in performance and ensure high reliability.

JP 2013-110069 A

However, while the above-mentioned conventional technology configuration allows for easy deterioration determination with a simple configuration, there is variation in the accuracy of the determination. For this reason, in actual operation, it is difficult to set the threshold value used for the deterioration determination, which may result in overdetermination, and in this respect, there is still room for improvement.

The present invention has been made to solve the above problems, and its purpose is to provide a degradation determination method and degradation determination device that can easily and accurately determine the degradation of a lithium-ion secondary battery.

A method for determining deterioration of a lithium ion secondary battery that solves the above problems includes the steps of: measuring a self-discharge capacity of a lithium ion secondary battery; calculating a negative electrode side reaction current consumed on the negative electrode side of the lithium ion secondary battery by dividing the self-discharge capacity by a discharge time; estimating an amount of a coating formed on the negative electrode based on the negative electrode side reaction current; calculating a degree of deterioration due to lithium precipitation occurring on the negative electrode due to the formation of a coating based on the amount of the coating as the lithium precipitation resistance of the lithium ion secondary battery; and determining a deterioration state of the lithium ion secondary battery based on the lithium precipitation resistance .

According to the above configuration, the degradation phenomenon occurring in the positive electrode and the negative electrode of the lithium ion secondary battery is separated, and the lithium deposition resistance , which is an index of the degradation state, is calculated by estimating the amount of the coating formed on the negative electrode. Furthermore, for example, the lithium deposition resistance according to the amount of the coating can be calculated according to the type of the lithium ion secondary battery to be judged. This makes it possible to accurately judge the degradation state of the lithium ion secondary battery. Furthermore, the negative electrode side reaction current is calculated and the amount of the coating is estimated by measuring the self-discharge capacity. This makes it possible to easily judge the degradation of the collected lithium ion secondary battery, even if there is no information on the usage history linked to the individual battery, such as the usage state and the environmental temperature.

A method for determining deterioration of a lithium ion secondary battery that solves the above problem preferably calculates the lithium precipitation resistance to have a smaller value as the amount of coating increases, and determines that the lithium ion secondary battery can be used when the lithium precipitation resistance is equal to or greater than a predetermined deterioration determination threshold.

In other words, the formation of the coating on the negative electrode is a rate-limiting reaction that depends on the amount of charge transfer at the electrode interface, and the deposition of lithium accompanying the formation of this coating causes the deterioration state of the negative electrode to progress. Therefore, with the above configuration, it is possible to easily and accurately determine the deterioration of a lithium-ion secondary battery.

A method for determining the deterioration of a lithium ion secondary battery that solves the above problem preferably includes a step of registering in advance in a storage device lithium deposition information indicating the relationship between the amount of coating and the lithium deposition resistance , and calculating the lithium deposition resistance by referring to the amount of coating in accordance with the lithium deposition information.

According to the above configuration, the lithium deposition resistance can be calculated quickly according to the amount of the coating film while reducing the calculation load. Furthermore, the lithium deposition information can be switched according to the type of the lithium ion secondary battery. This makes it possible to easily and accurately determine the deterioration of the lithium ion secondary battery.

The method for determining the deterioration of a lithium-ion secondary battery that solves the above problem preferably includes a step of storing the lithium-ion secondary battery for a predetermined storage period under a predetermined storage environment, and calculates the negative electrode side reaction current by using the change in capacity before and after storage as the self-discharge capacity and the storage period as the discharge time.

The above configuration makes it possible to easily and accurately measure the self-discharge capacity of a lithium-ion secondary battery and calculate the negative electrode side reaction current with a simple configuration. This makes it possible to more accurately determine the deterioration of a lithium-ion secondary battery.

A method for determining deterioration of a lithium ion secondary battery that solves the above-mentioned problems preferably includes a step of predicting and calculating over time the negative electrode side reaction current generated in the lithium ion secondary battery and the amount of film growing based on the negative electrode side reaction current, a step of calculating the lithium deposition resistance at a future time based on the predicted amount of film at the future time, and a step of estimating a remaining life of the lithium ion secondary battery by identifying the future time at which the lithium ion secondary battery will be unusable based on the lithium deposition resistance at the future time.

In other words, since the formation of the coating on the negative electrode is a rate-limiting reaction that depends on the amount of charge transfer at the electrode interface, it is possible to predict the negative electrode side reaction current and the amount of coating over time in the future, using the amount of coating on the negative electrode as the initial condition. Therefore, with the above configuration, it is possible to accurately estimate the remaining life of the lithium ion secondary battery. This allows the lithium ion secondary battery to be used effectively, taking into account the remaining life.

The method for determining the deterioration of a lithium-ion secondary battery that solves the above problem preferably includes a step of registering in advance data over time relating to the usage environment of the lithium-ion secondary battery in a storage device, and the step of predicting and calculating the amount of coating over time preferably includes a step of correcting the negative electrode side reaction current based on the data over time.

That is, the charge transfer rate at the electrode interface depends on the electrode potential and temperature of the usage environment. Therefore, with the above configuration, it is possible to accurately predict the negative electrode side reaction current and the amount of coating in the future. This makes it possible to more accurately estimate the remaining life of the lithium ion secondary battery.

A method for determining the deterioration of a lithium ion secondary battery that solves the above problem preferably includes a step of predicting and calculating the negative electrode side reaction current and the positive electrode side reaction current generated in the lithium ion secondary battery over time, a step of calculating the amount of capacity decrease of the lithium ion secondary battery at a future time based on the integral value of the negative electrode side reaction current and the integral value of the positive electrode side reaction current at the predicted future time, and a step of estimating the remaining life of the lithium ion secondary battery by identifying the future time at which the lithium ion secondary battery will become unusable based on the amount of capacity decrease at the future time.

According to the above configuration, the remaining life of the lithium ion secondary battery can be estimated with high accuracy.
A method for determining the degradation of a lithium-ion secondary battery that solves the above problem preferably includes at least one of a step of measuring a resistance of the lithium-ion secondary battery and determining a degradation state of the lithium-ion secondary battery based on the resistance, and a step of measuring a full charge capacity of the lithium-ion secondary battery and determining a degradation state of the lithium-ion secondary battery based on the full charge capacity.

The above configuration allows for more accurate degradation judgment of the lithium ion secondary battery. In particular, it is possible to avoid over-judgment that occurs when judging the degradation state based on resistance or full charge capacity, specifically, a situation in which the negative electrode side is judged to be unusable even when there is a margin for degradation. This allows for more effective use of the lithium ion secondary battery.

A degradation determination device for a lithium ion secondary battery that solves the above problems includes a self-discharge capacity measurement unit that measures the self-discharge capacity of a lithium ion secondary battery, a negative electrode side reaction current calculation unit that calculates a negative electrode side reaction current consumed on the negative electrode side of the lithium ion secondary battery by dividing the self-discharge capacity by a discharge time, a negative electrode film amount estimation unit that estimates an amount of a coating formed on the negative electrode based on the negative electrode side reaction current, a lithium deposition resistance calculation unit that calculates, based on the amount of coating, a degree of degradation due to lithium precipitation caused on the negative electrode due to the formation of a coating as the lithium deposition resistance of the lithium ion secondary battery, and a degradation state determination unit that determines a degradation state of the lithium ion secondary battery based on the lithium precipitation resistance .

The present invention makes it possible to accurately determine the deterioration of a lithium-ion secondary battery.

FIG. 1 is a schematic diagram of a lithium-ion secondary battery. FIG. 2 is a schematic diagram of a deterioration determination device. 4 is a flowchart showing a process for determining deterioration of a lithium ion secondary battery. FIG. 4 is an explanatory diagram showing the relationship between the negative electrode side reaction current and the coating amount of the negative electrode. FIG. 4 is an explanatory diagram showing the relationship between the coating amount of a negative electrode and lithium deposition resistance . 4 is a flowchart showing a processing procedure for calculating a negative electrode side reaction current. FIG. 4 is an explanatory diagram showing storage of recovered lithium-ion batteries and the change in capacity before and after storage. FIG. 4 is an explanatory diagram showing various conditions for remaining life estimation registered in a memory. 4 is a flowchart showing a processing procedure for estimating the remaining life of a lithium ion secondary battery based on predictions of a negative electrode side reaction current and a negative electrode coating amount. 10 is a flowchart showing a processing procedure of another example of remaining life estimation.

Hereinafter, an embodiment of a method and device for determining deterioration of a lithium ion secondary battery will be described with reference to the drawings.
1, a lithium ion secondary battery 1 is composed of a cell 10 that contains a positive electrode 3, a negative electrode 4, and a separator 5 together with an electrolyte (not shown). In general, a plurality of such cells 10 are combined and packaged depending on the intended use, such as an on-board power source.

For convenience of explanation, a so-called one-dimensional battery model is shown in FIG. 1, but in actual configuration, for example, the positive electrode 3, the negative electrode 4, and the separator 5 are laminated with a sheet-like outer shape. Furthermore, by rolling up this laminate, an electrode body 11 is formed in which the positive and negative electrodes and the separator 5 are alternately arranged in the radial direction with the separator 5 sandwiched between the positive electrode 3 and the negative electrode 4. That is, two separators 5 are used to form the electrode body 11. In many cases, the electrode body 11 has a flat outer shape by pressing the rolled positive electrode 3, the negative electrode 4, and the separator 5 from the outside in the radial direction. The lithium ion secondary battery 1 is configured to accommodate such an electrode body 11 together with a nonaqueous electrolyte solution or a nonaqueous electrolyte polymer as an electrolyte in a case 12 that constitutes the outer shell of the cell 10.

The positive electrode 3 and the negative electrode 4 are formed by applying a slurry containing an active material to a positive electrode collector 13 and a negative electrode collector 14, each having a sheet-like outer shape. Specifically, the positive electrode collector 13 is made of, for example, aluminum, and the positive electrode active material is a lithium transition metal oxide. The negative electrode collector 14 is made of, for example, copper, and the negative electrode active material is a carbon-based material. The case 12 of the lithium ion secondary battery 1 is provided with a positive electrode terminal 15 and a negative electrode terminal 16 that protrude to the outside. The lithium ion secondary battery 1 is configured such that the positive electrode collector 13 and the negative electrode collector 14 are electrically connected to the corresponding positive electrode terminal 15 and negative electrode terminal 16, respectively.

(Device and method for determining deterioration of lithium-ion secondary battery)
Next, a deterioration determination device for the lithium ion secondary battery 1 and a deterioration determination method thereof will be described.

As shown in FIG. 2, after being collected, a used lithium-ion secondary battery 1, for example, from an on-board power source, is connected to a deterioration determination device 21. Then, based on the deterioration state, it is determined whether or not the battery can be reused.

More specifically, the deterioration determination device 21 includes a charge/discharge unit 22 that charges and discharges the lithium ion secondary battery 1. The deterioration determination device 21 also includes a voltage measurement unit 23 that measures the voltage VB of the lithium ion secondary battery 1, and a current measurement unit 24 that measures the current IB. The deterioration determination device 21 also includes a temperature sensor 25 that measures the environmental temperature TB of the lithium ion secondary battery 1. The deterioration determination device 21 also includes a temperature management unit 26 that manages the environmental temperature TB of the lithium ion secondary battery 1.

In the deterioration determination device 21 of this embodiment, the operation of the charge/discharge unit 22 is controlled by the control device 30. Specifically, the control device 30 is configured as a microcomputer equipped with a memory 31 in which control programs and data are stored, along with an arithmetic processing circuit that executes arithmetic processing for control. Furthermore, detection data by the voltage measurement unit 23 and the current measurement unit 24 are also input to the control device 30. The operation of the temperature management unit 26 is also controlled by the control device 30.

That is, the deterioration determination device 21 can freely set the charge/discharge state and the environmental temperature TB of the lithium ion secondary battery 1 based on the control program executed by the control device 30. The deterioration determination device 21 of this embodiment is configured to adjust the charge/discharge state and the environmental temperature TB of the lithium ion secondary battery 1 while measuring various state quantities of the lithium ion secondary battery 1 based on the detection data of the voltage measurement unit 23 and the current measurement unit 24, thereby determining the deterioration state.

In more detail, as shown in the flowchart of FIG. 3, when the lithium ion secondary battery 1 is collected (step 101), the deterioration determination device 21 of this embodiment first measures the resistance R and full charge capacity R1 at the time of collection (step 102). Furthermore, the resistance R and full charge capacity Q1 at the time of collection are compared with predetermined deterioration determination thresholds Rth and Qth, respectively (steps 103 and 104). Then, if the resistance R at the time of collection exceeds the deterioration determination threshold Rth (R>Rth, step 103: NO), or if the full charge capacity Q1 at the time of collection is less than the deterioration determination threshold Qth (Q1<Qth, step 104: NO), the deterioration determination device 21 determines that the deterioration state is in a terminal state in which the battery cannot be reused (reusable, step 105).

In addition, when both of the deterioration determination conditions in steps 103 and 104 are satisfied (R≦Rth and Q1≧Qth, step 103: YES and step 104: YES), the deterioration determination device 21 of this embodiment subsequently measures the negative electrode side reaction current I_ne generated in the negative electrode 4 of the lithium ion secondary battery 1 (step 106). Next, the deterioration determination device 21 estimates the amount of film X_ne formed on the negative electrode 4 based on this negative electrode side reaction current I_ne (step 107). Furthermore, based on the amount of film X_ne on the negative electrode 4, the deterioration determination device 21 calculates the degree of deterioration resistance against lithium deposition generated on the negative electrode 4 due to the formation of the film as the lithium deposition resistance Z of the lithium ion secondary battery 1 (step 108). Then, the deterioration determination device 21 of this embodiment determines the deterioration state of the lithium ion secondary battery 1 based on this lithium deposition resistance Z (step 109).

That is, the following equation (1), which shows the electrode film growth model, can be converted to equation (2), which shows the relationship between the side reaction current I generated by charge transfer at the electrode interface and its integral value ∫Idt.

That is, the amount of charge transfer per unit time consumed to form the coating at the electrode interface is represented by the side reaction current I. Furthermore, as the resistance increases with the growth of the coating, the amount of charge transfer at the electrode interface gradually decreases. This leads to equation (1) showing that the film thickness x and the growth rate (dx/dt) are inversely proportional to each other, and equation (2) showing that the side reaction current I and the integral value ∫Idt showing the amount of coating on the electrode are inversely proportional to each other.

2 and 4, in the deterioration determination device 21 of this embodiment, the relationship between the negative electrode side reaction current I_ne and the amount of coating X_ne of the negative electrode 4 is registered in advance in the memory 31 of the control device 30 in the form of a map 33. In FIG. 4, the unit of the negative electrode side reaction current I_ne is "μA", and the unit of the amount of coating X_ne of the negative electrode 4 is "Ah". The deterioration determination device 21 of this embodiment estimates the amount of coating X_ne of the negative electrode 4 in the lithium ion secondary battery 1 by referring to the measured negative electrode side reaction current I_ne in this map 33.

2 and 5, in the deterioration determination device 21 of this embodiment, lithium deposition information indicating the relationship between the coating amount X_ne of the negative electrode 4 and the lithium deposition resistance Z is also registered in advance in the memory 31 of the control device 30 in the form of a map 34. Specifically, the map 34 holds a relationship between the lithium deposition resistance Z and the coating amount X_ne, the value of which gradually decreases as the coating amount X_ne of the negative electrode 4 increases. That is, as the coating amount X_ne of the negative electrode 4 increases, the amount of lithium deposited on the negative electrode 4 side increases by being taken in by the coating. Then, the deterioration determination device 21 of this embodiment calculates the lithium deposition resistance Z of the lithium ion secondary battery 1 by referring to the estimated coating amount X_ne of the negative electrode 4 in the map 34.

3 to 5, the deterioration determination device 21 of this embodiment compares the calculated lithium precipitation resistance Z with a predetermined deterioration determination threshold Zth in step 109. If the lithium precipitation resistance Z is equal to or greater than the deterioration determination threshold Zth (Z≧Zth, step 109: YES), the lithium ion secondary battery 1 is determined to be in a state in which it can be reused (step 110), and if it is less than the deterioration determination threshold Zth (Z<Zth, step 109: NO), the lithium ion secondary battery 1 is determined to be unreusable in step 105.

More specifically, as shown in the flowchart of FIG. 6 and in FIG. 7, the deterioration determination device 21 of this embodiment first measures the full charge capacity Q1 of the collected lithium ion secondary battery 1 at the time of collection (step 201).

Specifically, in the measurement of the full charge capacity Q1 in step 201, the lithium ion secondary battery 1 is first discharged to reduce the voltage VB to a lower limit voltage Vmin corresponding to a state of charge (SOC) of "0%, i.e., a fully discharged state. Next, the lithium ion secondary battery 1 is charged to increase the voltage VB to an upper limit voltage Vmax corresponding to a state of SOC of "100%, i.e., a fully charged state. For example, the lower limit voltage Vmin is "3.0 V" and the upper limit voltage Vmax is "4.1 V". Furthermore, the charge amount from the fully discharged state to the fully charged state, i.e., the current IB flowing while charging the lithium ion secondary battery 1, is measured. Then, the deterioration determination device 21 of this embodiment uses the measured full charge capacity Q1 at the time of recovery for the deterioration determination based on the full charge capacity Q1 at the time of recovery as described above (see FIG. 3, step 104).

Next, the deterioration determination device 21 of this embodiment sets a reference voltage Vref to the voltage VB of the lithium ion secondary battery 1, and measures the reference charge capacity Q2 at this reference voltage Vref (step 202). Specifically, the reference voltage Vref is set to any value between the lower limit voltage Vmin and the upper limit voltage Vmax, for example, "3.8 V". In this case as well, the reference charge capacity Q2 is measured based on the charge amount from when the voltage VB of the lithium ion secondary battery 1 reaches the reference voltage Vref from the lower limit voltage Vmin.

Furthermore, the deterioration determination device 21 of this embodiment stores the lithium ion secondary battery 1 adjusted to this reference voltage Vref for a predetermined storage period t_st and in a predetermined storage environment (step 203). Specifically, for example, the predetermined storage period t_st is set to "about several days". In addition, as the predetermined storage environment, the environmental temperature TB of the lithium ion secondary battery 1 is maintained at a predetermined temperature T_st, for example, about "70°C". Then, after storing the lithium ion secondary battery 1, the deterioration determination device 21 measures its remaining capacity Q3 (step 204).

The measurement of the remaining capacity Q3 in step 204 is performed by discharging the lithium ion secondary battery 1 after storage until its voltage VB reaches the lower limit voltage Vmin, and measuring the current IB that flows during this time. The degradation determination device 21 of this embodiment then subtracts this remaining capacity Q3 after storage from the reference charge capacity Q2 before storage measured in step 102 above, that is, calculates the self-discharge capacity Qsd of the lithium ion secondary battery 1 based on the change in capacity before and after storage (Qsd = Q2 - Q3, step 205).

The deterioration determination device 21 further calculates the negative electrode side reaction current I_ne of the lithium ion secondary battery 1 by dividing the self-discharge capacity Qsd calculated in step 205 by the storage period t_st, which is the discharge time (I_ne = Qsd / t_st, step 206). The deterioration determination device 21 of this embodiment is configured to use the negative electrode side reaction current I_ne calculated in step 206 to estimate the amount of film X_ne formed on the negative electrode 4, calculate the deterioration determination threshold Zth based on this amount of film X_ne, and perform deterioration determination (see FIG. 3, steps 106 to 109).

The full charge capacity Q4 after storage is measured (step 207), and the capacity loss amount Qloss of the lithium ion secondary battery 1 can be calculated by subtracting this full charge capacity Q4 after storage from the full charge capacity Q1 at the time of recovery (Qloss = Q1 - Q4, step 208). In this case, the full charge capacity Q4 after storage can also be measured based on the charge amount until the voltage VB of the lithium ion secondary battery 1 reaches the upper limit voltage Vmax from the lower limit voltage Vmin. The capacity loss amount Qloss is divided by the storage period t_st, and the value is subtracted from the negative electrode side reaction current I_ne calculated in step 206 above to calculate the positive electrode side reaction current I_pe of the lithium ion secondary battery 1 (I_pe = I_ne - (Qloss/t_st), step 209).

The deterioration determination device 21 of this embodiment also predicts and calculates, over time, the negative electrode side reaction current I_ne generated in the lithium ion secondary battery 1 and the amount of film X_ne of the negative electrode 4 that grows based on the negative electrode side reaction current I_ne. Furthermore, the deterioration determination device 21 calculates the lithium deposition tolerance Z at the future time t based on the predicted amount of film X_ne at the future time t. Then, the deterioration determination device 21 of this embodiment specifies the future time t at which the lithium ion secondary battery 1 will become unusable based on the lithium deposition tolerance Z at the future time t, thereby estimating the remaining life N of the lithium ion secondary battery 1.

As shown in the flowcharts of Figures 8 and 9, when estimating the remaining life N of a lithium-ion secondary battery 1 using the deterioration determination device 21 of this embodiment, first, various conditions that serve as initial conditions for the remaining life estimation are registered in the memory 31 of the control device 30 (see Figure 2) (step 301).

Specifically, the conditions that are registered in advance in the memory 31 as the initial conditions include the coating amount X_ne of the negative electrode 4 estimated as described above (see Figures 3 and 4), and the usage environment information D_evr of the lithium ion secondary battery 1.

In the deterioration determination device 21 of this embodiment, the value of the coating amount X_ne estimated when calculating the lithium deposition resistance Z of the recovered lithium ion secondary battery 1 is registered in the memory 31 of the control device 30 as an initial value X_ne0 at the start of the prediction. Furthermore, independently of this initial value X_ne0, the coating amount X_ne at the future time t, which grows with the passage of time, is updated as needed as the prediction progresses and is stored in the memory 31 of the control device 30. As will be described later, in the deterioration determination device 21 of this embodiment, the initial value X_ne0 of the coating amount X_ne is used in the update calculation of the coating amount X_ne at the future time t. Then, the deterioration determination device 21 of this embodiment calculates the lithium deposition resistance Z at the future time t based on the coating amount X_ne at the future time t calculated by this prediction.

In the deterioration determination device 21 of this embodiment, the usage environment information D_evr is composed of voltage data over time D_vb of the lithium ion secondary battery 1 predicted during future use, and temperature data over time D_tb of the lithium ion secondary battery 1 predicted during future use. The voltage data over time D_vb is stored in a state in which the negative electrode potential V_ne and the positive electrode potential V_pe are separated for each elapsed time. In the deterioration determination device 21 of this embodiment, the voltage data over time D_vb and the temperature data over time D_tb are stored in the form of a map, which represents the relationship between the elapsed time and the cell voltage, and the relationship between the elapsed time and the temperature information.

Furthermore, a correction map M_ne for correcting the anode side reaction current I_ne at the future time t based on the use environment information D_evr is registered in the memory 31. That is, the correction map M_cor holds the relationship between the anode potential V_ne and the environmental temperature TB and the correction value α of the anode side reaction current I_ne, which are obtained by an experiment, a simulation, or the like. The deterioration determination device 21 of this embodiment is configured to perform deterioration determination of the lithium ion secondary battery 1 at the future time t by referring to this correction map M_cor and correcting the anode side reaction current I_ne based on the anode potential V_ne and the environmental temperature TB at the future time t, while estimating the coating amount X_ne and calculating the lithium deposition resistance Z.

In detail, when the deterioration determination device 21 registers various conditions that are the initial conditions for the remaining life estimation in step 301, it first sets a time counter for measuring the future time t (t=0, step 302). For convenience of explanation, "one count" of the future time t by the time counter is set to a unit time of the negative electrode side reaction current I_ne ("1 s (second)"). Next, the deterioration determination device 21 calculates the lithium deposition resistance Z based on the coating amount X_ne of the negative electrode 4 registered in the memory 31 (step 303). In the deterioration determination device 21 of this embodiment, the calculation of the lithium deposition resistance Z is performed using the map 34 stored in the memory 31, as in the determination of the deterioration state after recovery shown in the flowchart of FIG. 3 (see FIG. 5). Then, the deterioration determination device 21 of this embodiment determines whether the deterioration state of the lithium ion secondary battery 1 is such that the lithium ion secondary battery 1 cannot be used based on a comparison between this lithium precipitation resistance Z and the deterioration determination threshold value Zth (step 304).

9 is performed for lithium ion secondary batteries 1 that have been determined to be reusable (see FIG. 3, step 110) in the above-mentioned post-recovery degradation state determination. Therefore, immediately after the start of remaining life estimation (t=0), in step 304, it is determined that the lithium precipitation resistance Z is equal to or greater than the degradation determination threshold value Zth (Z≧Zth, step 304: NO).

In this step 304, if it is determined that the lithium ion secondary battery 1 can be used, the deterioration determination device 21 then increments its time counter (t = t + 1, step 305). Next, the deterioration determination device 21 calculates the value of the negative electrode side reaction current I_ne based on the coating amount X_ne of the negative electrode 4 registered in the memory 31 (step 306). In addition, in the deterioration determination device 21 of this embodiment, the calculation of this negative electrode side reaction current I_ne is performed using the above map 33 (see FIG. 4) stored in the memory 31. Furthermore, the deterioration determination device 21 calculates a correction value α of the negative electrode side reaction current I_ne at the future time t based on the usage environment information D_evr and the correction map M_cor also registered in the memory 31 (step 307). Then, the correction value α is used to perform the correction calculation of the negative electrode side reaction current I_ne (I_ne' = I_ne + α, step 308).

Next, the deterioration determination device 21 calculates the integral value ∫Idt_ne of the negative electrode side reaction current I_ne at the future time t (step 309). Note that the deterioration determination device 21 of this embodiment stores the value of the negative electrode side reaction current I_ne calculated in the above step 306 in the memory 31 as the negative electrode side reaction current transition data DI_ne over time. Then, based on this negative electrode side reaction current transition data D_ne, the integral value ∫Idt_ne of the negative electrode side reaction current I_ne is calculated.

Furthermore, the deterioration determination device 21 updates the coating amount X_ne of the negative electrode 4 by adding the integral value ∫Idt_ne of the negative electrode side reaction current I_ne calculated in step 309 based on the above formulas (1) and (2) to the initial value X_ne0 of the coating amount X_ne registered in the memory 31 in step 301 (X_ne = X_ne0 + ∫Idt_ne, step 310). Then, based on the new value of the coating amount X_ne updated in step 301, the processing of the above steps 303 and 304 is executed again.

That is, the deterioration determination device 21 of this embodiment repeatedly executes the processes of steps 303 to 310 described above until it is determined in step 304 that the value of the lithium precipitation resistance Z at the future time t is less than the deterioration determination threshold value Zth, in other words, that the lithium ion secondary battery 1 is unusable (Z<Zth, step 304: YES).Then, the future time t at which the lithium ion secondary battery 1 will be unusable is specified (step 311), and this is converted into the remaining life N of the lithium ion secondary battery 1 (step 312).

The remaining life N is expressed in units of, for example, "days" or "years." The deterioration determination device 21 of this embodiment compares the estimated remaining life N with a predetermined shipping threshold Nth (step 313). If the estimated remaining life N is equal to or greater than the shipping threshold Nth, the lithium ion secondary battery 1 is permitted to be shipped (step 314), and if it is less than the shipping threshold Nth, the lithium ion secondary battery 1 is determined not to be eligible for shipping (not eligible for shipping, step 315).

Next, the operation of this embodiment will be described.
As shown in FIG. 2, in this embodiment, a control device 30 constituting the deterioration determination device 21 functions as a self-discharge capacity measurement unit 30a, a negative electrode side reaction current calculation unit 30b, a negative electrode film amount estimation unit 30c, a lithium precipitation resistance calculation unit 30d, and a deterioration state determination unit 30e.

That is, in the deterioration determination device 21 of the present embodiment, the self-discharge capacity Qsd of the lithium ion secondary battery 1 is detected by measuring the capacity change before and after storage of the collected lithium ion secondary battery 1 based on the program executed by the control device 30. Next, the negative electrode side reaction current I_ne consumed on the negative electrode 4 side of the lithium ion secondary battery 1 is measured by dividing the self-discharge capacity Qsd by the storage period t_st, which is the discharge time. Next, the amount of film X_ne formed on the negative electrode 4 is estimated based on the negative electrode side reaction current I_ne. Furthermore, based on the amount of film X_ne, the degree of deterioration due to the deposition of lithium on the negative electrode 4 caused by the formation of the film is calculated as the lithium deposition resistance Z of the lithium ion secondary battery 1. Then, based on the lithium deposition resistance Z, the deterioration state of the lithium ion secondary battery 1 is determined.

Next, the effects of this embodiment will be described.
(1) According to the above configuration, the deterioration phenomenon occurring in the positive electrode 3 and the negative electrode 4 of the lithium ion secondary battery 1 is separated, and the lithium deposition tolerance Z, which is a tolerance to the deteriorated state, is calculated by estimating the amount of coating X_ne formed on the negative electrode 4. Furthermore, for example, the lithium deposition tolerance Z according to the amount of coating X_ne can be calculated according to the type of the lithium ion secondary battery 1 to be judged. This makes it possible to accurately judge the deteriorated state of the lithium ion secondary battery 1. Furthermore, the negative electrode side reaction current I_ne is calculated and the amount of coating X_ne is estimated by measuring the self-discharge capacity Qsd. This makes it possible to easily judge the deterioration of the collected lithium ion secondary battery 1, even if there is no information on the usage history linked to the individual battery, such as the usage state and the environmental temperature.

(2) The deterioration determination device 21 calculates a smaller value of the lithium deposition resistance Z as the coating amount X_ne of the negative electrode 4 increases. Then, when the lithium deposition resistance Z is equal to or greater than a predetermined deterioration determination threshold value Zth (Z≧Zth), the deterioration determination device 21 determines that the lithium ion secondary battery 1 can be used.

In other words, the formation of the coating on the negative electrode 4 is a rate-limiting reaction that depends on the amount of charge transfer at the electrode interface, and the deposition of lithium accompanying the formation of this coating causes the deterioration state of the negative electrode 4 to progress. Therefore, with the above configuration, the deterioration of the lithium-ion secondary battery 1 can be easily and accurately determined.

(3) In the memory 31 serving as a storage device, lithium deposition information indicating the relationship between the coating amount X_ne of the negative electrode 4 and the lithium deposition resistance Z is registered in advance in the form of a map 34. Then, the deterioration determination device 21 calculates the lithium deposition resistance Z by referring to the map 34 for the estimated coating amount X_ne of the negative electrode 4.

According to the above configuration, it is possible to quickly calculate the lithium deposition resistance Z corresponding to the coating amount X_ne while reducing the calculation load. Furthermore, it is also possible to switch the map 34 of the lithium deposition information according to the model of the lithium ion secondary battery 1. This makes it possible to easily and accurately determine the deterioration of the lithium ion secondary battery 1.

(4) The recovered lithium ion secondary battery 1 is stored in a specified storage environment that maintains a specified temperature T_st for a specified storage period t_st. The deterioration determination device 21 then determines the capacity change before and after storage as the self-discharge capacity Qsd of the lithium ion secondary battery 1, and calculates the negative electrode side reaction current I_ne using the storage period t_st as the discharge time.

The above configuration makes it possible to easily and accurately measure the self-discharge capacity Qsd of the lithium-ion secondary battery 1 and calculate the negative electrode side reaction current I_ne with a simple configuration. This makes it possible to more accurately determine the deterioration of the lithium-ion secondary battery 1.

(5) The deterioration determination device 21 predicts and calculates the negative electrode side reaction current I_ne generated in the lithium ion secondary battery 1 and the amount of film X_ne of the negative electrode 4 that grows based on the negative electrode side reaction current I_ne over time. Furthermore, the deterioration determination device 21 calculates the lithium deposition tolerance Z at the future time t based on the predicted amount of film X_ne at the future time t. Then, the deterioration determination device 21 specifies the future time t at which the lithium ion secondary battery 1 will become unusable based on the lithium deposition tolerance Z at the future time t, thereby estimating the remaining life N of the lithium ion secondary battery 1.

In other words, since the formation of the coating on the negative electrode 4 is a rate-limiting reaction depending on the amount of charge transfer at the electrode interface, the amount of coating X_ne on the negative electrode 4 can be used as an initial condition to predict the negative electrode side reaction current I_ne and the amount of coating X_ne at future time t over time. Therefore, with the above configuration, the remaining life N of the lithium ion secondary battery 1 can be estimated with high accuracy. This allows the lithium ion secondary battery 1 to be effectively reused based on the remaining life N.

(6) In the memory 31 as a storage device, usage environment information D_evr including voltage time data D_vb and temperature time data D_tb predicted for future use is registered in advance as time-lapse data related to the usage environment of the lithium-ion secondary battery 1. The deterioration determination device 21 then corrects the negative electrode side reaction current I_ne based on the usage environment information D_evr, and predicts the coating amount X_ne of the negative electrode 4 at the future time t.

That is, the charge transfer rate at the electrode interface depends on the electrode potential and temperature. Therefore, with the above configuration, it is possible to accurately predict the negative electrode side reaction current I_ne and the coating amount X_ne at future time t. This makes it possible to more accurately estimate the remaining life N of the lithium ion secondary battery 1.

(7) The deterioration determination device 21 measures the resistance R and full charge capacity Q1 of the recovered lithium ion secondary battery 1. Furthermore, the deterioration determination device 21 determines the deterioration state of the lithium ion secondary battery 1 based on the resistance R and full charge capacity Q1. Then, when both of these deterioration determination conditions are satisfied, the deterioration state of the lithium ion secondary battery 1 is determined by estimating the amount of film X_ne formed on the negative electrode 4 by measuring the negative electrode side reaction current I_ne and calculating the lithium deposition resistance Z based on this amount of film X_ne.

The above configuration allows for more accurate degradation judgment of the lithium ion secondary battery 1. In particular, it is possible to avoid over-judgment that occurs when the degradation state is judged based only on the resistance R and the full charge capacity Q1, specifically, a situation in which it is judged that the battery cannot be reused even when there is a margin for degradation on the negative electrode 4 side. This allows for more effective reuse of the lithium ion secondary battery 1.

The above embodiment can be modified as follows. The above embodiment and the following modified examples can be combined together as long as they are not technically inconsistent.

In the above embodiment, when the recovered lithium ion secondary battery 1 satisfies both the deterioration state determination based on the measurement of its resistance R and full charge capacity Q1 (R≦Rth and Q1≧Qth), the deterioration state determination is performed by measuring the negative electrode side reaction current I_ne, estimating the coating amount X_ne, and calculating the lithium deposition resistance Z. However, the present invention is not limited to this, and a configuration may be adopted in which either one of the deterioration state determination based on the measurement of the resistance R or the deterioration state determination based on the full charge capacity Q1 is combined with the deterioration state determination based on the lithium deposition resistance Z. The order of the determinations may also be arbitrarily changed, for example, by performing the deterioration state determination based on the lithium deposition resistance Z first.

- In the above embodiment, the relationship between the negative electrode side reaction current I_ne and the coating amount X_ne of the negative electrode 4 is registered in advance in the form of a map 33 in the memory 31 as a storage device, but a calculation formula may be used to determine the coating amount X_ne corresponding to the measured negative electrode side reaction current I_ne.

In the above embodiment, the relationship between the coating amount X_ne of the negative electrode 4 and the lithium deposition resistance Z is registered in advance in the memory 31 as a storage device in the form of a map 34. The map 34 holds a relationship between the coating amount X_ne and the lithium deposition resistance Z, the value of which gradually decreases in a substantially linear manner as the coating amount X_ne of the negative electrode 4 increases. However, the present invention is not limited to this, and the relationship between the coating amount X_ne of the negative electrode 4 and the lithium deposition resistance Z may be defined such that, for example, the value of the lithium deposition resistance Z decreases in a stepwise manner as the coating amount X_ne increases.

- The reference voltage Vref before storing the lithium ion secondary battery 1 may be changed arbitrarily between the lower limit voltage Vmin and the upper limit voltage Vmax. For example, the upper limit voltage Vmax may be set as the reference voltage Vref before storage. This makes it possible to omit the step of measuring the reference charge capacity Q2 (Vref = Vmax, Q2 = Q1).

- When storing the lithium ion secondary battery 1, the specified storage period t_st and the specified temperature T_st that is the specified storage condition may be changed arbitrarily. Furthermore, if it is possible to measure the self-discharge capacity Qsd, it is not necessary to store the lithium ion secondary battery 1.

In the above embodiment, the coating amount X_ne of the negative electrode 4 obtained in advance is registered in the memory 31 serving as a storage device as various conditions that serve as initial conditions for remaining life estimation. However, a configuration may also be adopted in which a negative electrode side reaction current I_ne or lithium deposition resistance Z that is measured in advance is registered, and the corresponding coating amount X_ne is obtained from the maps 33 and 34.

-Also, a configuration may be adopted in which "one count" of the future time t by the time counter is set to a time longer than the unit time ("one second") of the negative electrode side reaction current I_ne, such as "1 h" or "1 d," and the negative electrode side reaction current I_ne and the coating amount X_ne at that future time t are predicted. In this case, for example, the interval integral value of the negative electrode side reaction current I_ne is calculated for each count of the time counter. Then, by integrating this value over time, the coating amount X_ne of the negative electrode 4 at the future time t can be calculated.

In the above embodiment, the remaining life of the lithium ion secondary battery 1 is estimated by predicting the lithium deposition resistance Z at the future time t from the coating amount X_ne of the negative electrode 4.
However, the present invention is not limited to this, and may be configured to predict the amount of capacity loss Qloss at a future time t, and then estimate the remaining life of the lithium ion secondary battery 1 based on the predicted amount of capacity loss Qloss.

That is, as shown in Figures 6 and 7, the self-discharge capacity Qsd' of the lithium-ion secondary battery 1 can be obtained by calculating the integral value ∫Idt_ne of the negative electrode side reaction current I_ne (see step 206). Then, the capacity loss amount Qloss can be obtained by subtracting the integral value ∫Idt_pe of the positive electrode side reaction current I_pe from the integral value ∫Idt_ne of the negative electrode side reaction current I_ne (see step 209).

In consideration of this, as shown in the flowchart of FIG. 10, in addition to the prediction calculation of the negative electrode side reaction current I_ne at future time t and its integral value ∫Idt_ne corresponding to the coating amount X_ne (steps 406 and 407), the prediction calculation of the positive electrode side reaction current I_pe at future time t and its integral value ∫Idt_pe is performed (steps 408 to 411). In step 411, "∫Idt_pe0" is the initial value of the integral value ∫Idt_pe registered in step 401. Furthermore, the capacity loss amount Qloss at future time t is calculated by subtracting the integral value ∫Idt_pe of the positive electrode side reaction current I_pe from the integral value ∫Idt_ne of the negative electrode side reaction current I_ne at future time t (Qloss = ∫Idt_ne - ∫Idt_pe, step 403). Then, the remaining life is estimated by comparing the capacity loss Qloss at future time t with the deterioration determination threshold Qth_loss (step 404).

Note that the processes in step 402, steps 405 to 407, and step 412 and onward in the flowchart in FIG. 10 are the same as the processes in step 302, steps 305 to 310, and step 311 and onward in the flowchart in FIG. 9, respectively.

That is, the positive electrode side reaction current I_pe can be obtained by subtracting the differential value dQloss of the capacity loss amount Qloss from the negative electrode side reaction current I_ne (I_pe = I_ne' - dQloss, step 408, see step 209 in FIG. 6). In this example, similar to the negative electrode side reaction current I_ne, a correction calculation is also performed on the positive electrode side reaction current I_pe based on the usage environment information D_evr (step 409). Furthermore, the integral value ∫Idt_pe' of the positive electrode side reaction current I_pe is calculated (step 410), and the ∫Idt_pe registered in the memory 31 is updated with the new value ∫Idt_pe' (step 411). Then, in step 404, the process of steps 403 to 411 is repeated while incrementing the time counter (t = t + 1, step 405) until the value of the capacity loss amount Qloss during the initial back time exceeds the deterioration determination threshold Qth_loss (Qloss > Qth_loss, step 404: YES).

Even if such a configuration is adopted, the remaining life N of the lithium ion secondary battery 1 can be estimated with high accuracy, as in the above embodiment.

REFERENCE SIGNS LIST 1...Lithium ion secondary battery 4...Negative electrode 21...Deterioration determination device Qsd...Self-discharge capacity t_st...Storage period (discharge time)
I_ne: Negative electrode side reaction current X_ne: Amount of film Z: Lithium deposition resistance

Claims (8)

Measuring the self-discharge capacity of the lithium ion secondary battery;
A step of calculating a negative electrode side reaction current consumed on the negative electrode side of the lithium ion secondary battery by dividing the self-discharge capacity by a discharge time;
estimating an amount of a coating formed on the negative electrode based on the negative electrode side reaction current;
a step of registering in advance in a storage device lithium deposition information indicating a relationship between the amount of the coating film and lithium deposition resistance, which is a degree of deterioration resistance against lithium deposition occurring on the negative electrode due to the formation of the coating film ;
calculating the lithium deposition resistance based on the amount of the coating film by referring to the lithium deposition information;
determining a degradation state of the lithium ion secondary battery based on the lithium precipitation resistance . The lithium precipitation resistance is calculated so that the lithium precipitation resistance has a smaller value as the amount of the coating film increases, and
The method for determining deterioration of a lithium ion secondary battery according to claim 1 , further comprising the step of determining that the lithium ion secondary battery is usable when the lithium precipitation resistance is equal to or greater than a predetermined deterioration determination threshold value. storing the lithium ion secondary battery in a predetermined storage environment for a predetermined storage period;
3. The method for determining deterioration of a lithium ion secondary battery according to claim 1, further comprising the steps of: calculating the negative electrode side reaction current by using a change in capacity before and after storage as the self-discharge capacity and the storage period as the discharge time. a step of predicting and calculating the negative electrode side reaction current generated in the lithium ion secondary battery and the amount of the coating film growing based on the negative electrode side reaction current over time;
calculating the lithium deposition resistance in the future time based on the film amount predicted in the future time;
and estimating a remaining life of the lithium ion secondary battery by specifying the future time at which the lithium ion secondary battery will become unusable based on the lithium precipitation resistance of the future time. a step of registering, in advance, time-dependent data relating to a usage environment of the lithium ion secondary battery in a storage device;
5. The method for determining deterioration of a lithium ion secondary battery according to claim 4, wherein the step of predicting and calculating the amount of coating over time includes a step of correcting the negative electrode side reaction current based on the data over time. predicting and calculating the negative electrode side reaction current and the positive electrode side reaction current generated in the lithium ion secondary battery over time;
calculating an amount of capacity decrease of the lithium ion secondary battery in the future time based on an integral value of the negative electrode side reaction current and an integral value of the positive electrode side reaction current in the predicted future time;
and estimating a remaining life of the lithium ion secondary battery by identifying the future time at which the lithium ion secondary battery will become unusable based on the amount of capacity decrease in the future time. The degradation determination method for a lithium ion secondary battery according to any one of claims 1 to 6, comprising at least one of a step of measuring a resistance of the lithium ion secondary battery and determining a degradation state of the lithium ion secondary battery based on the resistance, and a step of measuring a full charge capacity of the lithium ion secondary battery and determining a degradation state of the lithium ion secondary battery based on the full charge capacity. A self-discharge capacity measuring unit for measuring a self-discharge capacity of the lithium ion secondary battery;
a negative electrode side reaction current calculation unit that calculates a negative electrode side reaction current consumed on the negative electrode side of the lithium ion secondary battery by dividing the self-discharge capacity by a discharge time;
a negative electrode film amount estimation unit that estimates an amount of a film formed on the negative electrode based on the negative electrode side reaction current;
a storage device that preregisters lithium deposition information indicating a relationship between the coating amount and lithium deposition resistance ;
a lithium precipitation resistance calculation unit that calculates the degree of deterioration resistance against lithium precipitation occurring on the negative electrode due to the formation of the coating based on the amount of the coating by referring to the lithium precipitation information, as the lithium precipitation resistance of the lithium ion secondary battery;
a degradation state determination unit that determines a degradation state of the lithium ion secondary battery based on the lithium precipitation resistance .