Inspection method and inspection device

Abstract

To suppress an increase in inspection time when pass / fail determination is performed using a threshold value set for each inspection object.SOLUTION: An inspection method obtains a V-dQ / dV characteristic for a lithium-ion battery; extracts a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; calculates a first predicted value by substituting the first dQ / dV value and the second dQ / dV value into a first prediction formula for calculating a first predicted value, which is a predicted value of a deviation amount of an initial capacity of the lithium-ion battery from a reference value; calculates a second predicted value by substituting the first predicted value into a second prediction formula for calculating a second predicted value, which is a predicted value of a deviation amount of an SOC-OCV characteristic of the lithium-ion battery from a reference value; derives the SOC-OCV characteristic of the lithium-ion battery based on the second predicted value; drives a threshold value for determining an open circuit voltage when the lithium-ion battery at a predetermined charge rate is left for a predetermined period of time, based on the SOC-OCV characteristic; and performs determination using the threshold value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The disclosed technology relates to a method and apparatus for inspecting lithium ion batteries. [Background technology]

[0002] The following techniques are known as techniques for inspecting lithium-ion batteries. Patent Document 1 describes an inspection method in which a lithium-ion battery is charged at least once, the amount of voltage change in the lithium-ion battery after it is left for a predetermined period of time after charging is determined, and the amount of voltage change is compared with a predetermined threshold value to determine whether the lithium-ion battery is good or bad. If the capacity of the lithium-ion battery being inspected is smaller than the design capacity, the predetermined threshold value is changed to a larger value. On the other hand, if the capacity of the lithium-ion battery being inspected is larger than the design capacity, the predetermined threshold value is changed to a smaller value.

[0003] Patent Document 2 describes an inspection system that compares the actual dQ / dV value at the time of initial charging of a secondary battery under inspection with information on a V-dQ / dV curve to determine whether it corresponds to a characteristic point on the curve, and if it does not, detects this as an abnormality indicating that the long-term capacity reliability of the secondary battery cannot be ensured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-125091 A [Patent Document 2] JP 2014-002055 A Summary of the Invention [Problem to be solved by the invention]

[0005] It is known that a lithium-ion battery with a micro-short circuit has a larger voltage drop after aging than a normal lithium-ion battery. That is, the difference in open circuit voltage (OCV) between a lithium-ion battery with a micro-short circuit and a normal lithium-ion battery becomes significant as time passes from a common state of charge (SOC).

[0006] Therefore, in the manufacturing process of lithium-ion batteries, a self-discharge test is performed to screen out lithium-ion batteries with micro-short circuits as non-conforming products. In the self-discharge test, a lithium-ion battery with a predetermined charge rate is left for a predetermined period of time, and the open-circuit voltage of the lithium-ion battery is determined using a threshold value Vth.

[0007] Since a margin is usually added to the threshold value Vth, if the threshold value Vth is set to a fixed value, a loss occurs due to a failure judgment being made for a test object that should have been a pass judgment. For this reason, it is preferable to set the threshold value Vth for each test object.

[0008] In the above-mentioned Patent Document 1, a threshold value Vth for determining the differential voltage ΔV is set based on the capacity of the lithium ion battery to be tested. However, this method requires measurement of the capacity of the lithium ion battery to be tested, which increases the test time.

[0009] The disclosed technology has been made in consideration of the above points, and aims to prevent the inspection time from becoming too long when determining pass / fail using a threshold value set for each inspection object. [Means for solving the problem]

[0010] An inspection method according to the disclosed technique is a method for inspecting a lithium-ion battery, comprising the steps of: acquiring a V-dQ / dV characteristic indicating a relationship between an inter-electrode voltage and dQ / dV during an initial charge of the lithium-ion battery; extracting a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; a prediction formula for calculating a first predicted value, which is a predicted value of a deviation of an initial capacity of the lithium ion battery from a reference value, the first predicted value being calculated by substituting the extracted first dQ / dV value and the second dQ / dV value into a first prediction formula including the first dQ / dV value and the second dQ / dV value as variables; a prediction formula for calculating a second predicted value, which is a predicted value of a deviation of an SOC-OCV characteristic indicating a relationship between a charging rate and an open-circuit voltage of the lithium ion battery, the second predicted value being calculated by substituting the calculated first predicted value into a second prediction formula including the deviation of an initial capacity of the lithium ion battery from a reference value as a variable; deriving the SOC-OCV characteristic of the lithium ion battery based on the calculated second predicted value; deriving a threshold value for determining the open-circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; and making the determination using the derived threshold value. The first dQ / dV value is the dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode of the lithium ion battery, which is derived from an additive contained in the electrolyte of the lithium ion battery, and the second dQ / dV value is the dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, which is derived from an organic solvent contained in the electrolyte of the lithium ion battery.

[0011] The first dQ / dV value may be a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from LiBOB contained in the electrolyte of the lithium ion battery.

[0012] The second dQ / dV value may be a dQ / dV value of a characteristic portion appearing on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from EC contained in the electrolyte of the lithium ion battery.

[0013] The second predicted value may further include a positive electrode capacity of the lithium ion battery as a variable, and the second predicted value may be calculated by substituting the positive electrode capacity and the first predicted value into the second prediction formula.

[0014] Based on the derived SOC-OCV characteristic, an allowable fluctuation amount, which is the amount of fluctuation in the open-circuit voltage of the lithium-ion battery when the charging rate changes to a limit that is allowable as the amount of fluctuation in the charging rate of the lithium-ion battery when the lithium-ion battery is left at a predetermined charging rate for a predetermined period of time, may be derived as the threshold value, and a differential voltage, which is the difference in the open-circuit voltage of the lithium-ion battery before and after the lithium-ion battery is left at a predetermined charging rate for a predetermined period of time, may be determined using the derived threshold value.

[0015] Based on the derived SOC-OCV characteristic, an allowable fluctuation amount, which is the amount of fluctuation in the open-circuit voltage of the lithium-ion battery when the charging rate changes to a limit allowable as the amount of fluctuation in the charging rate of the lithium-ion battery when the lithium-ion battery is left alone for a predetermined period of time at a predetermined charging rate, may be derived, and a threshold value may be derived from a measured value of the open-circuit voltage of the lithium-ion battery before being left alone when the lithium-ion battery is left alone at a predetermined charging rate for a predetermined period of time, by fluctuating by the derived allowable fluctuation amount, and the measured value of the open-circuit voltage of the lithium-ion battery after being left alone when the lithium-ion battery is left alone at a predetermined charging rate for a predetermined period of time may be determined using the derived threshold value.

[0016] The inspection device according to the disclosed technique is an inspection device for a lithium-ion battery, comprising: an acquisition unit that acquires a V-dQ / dV characteristic that indicates the relationship between the inter-electrode voltage and dQ / dV during an initial charge of the lithium-ion battery; an extraction unit that extracts a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; a first calculation unit that calculates a first predicted value, which is a predicted value of the deviation of the initial capacity of the lithium-ion battery from a reference value, by substituting the extracted first dQ / dV value and the second dQ / dV value into a first prediction formula that includes the first dQ / dV value and the second dQ / dV value as variables; and a second calculation unit that calculates the relationship between the charging rate and the open-circuit voltage of the lithium-ion battery. the second prediction formula including, as a variable, the amount of deviation of the initial capacity of the lithium ion battery from a reference value; a characteristic derivation unit that derives the SOC-OCV characteristic of the lithium ion battery based on the calculated second predicted value; a threshold derivation unit that derives, based on the derived SOC-OCV characteristic, a threshold for making a judgment about the open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time; and a judgment unit that makes the judgment using the derived threshold. The first dQ / dV value is the dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode of the lithium ion battery, which is derived from an additive contained in the electrolyte of the lithium ion battery, and the second dQ / dV value is the dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, which is derived from an organic solvent contained in the electrolyte of the lithium ion battery.

[0017] The threshold derivation unit may derive, as the threshold, an amount of change in the open-circuit voltage of the lithium-ion battery when the charging rate changes to a limit that is permissible as an amount of change in the charging rate of the lithium-ion battery when the lithium-ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic. The determination unit may determine, using the derived threshold, a differential voltage that is a difference between the open-circuit voltage of the lithium-ion battery before and after the lithium-ion battery is left at a predetermined charging rate for a predetermined period of time.

[0018] The threshold derivation unit may derive an allowable fluctuation amount, which is the amount of fluctuation in the open-circuit voltage of the lithium-ion battery when the charging rate changes to a limit allowable as the amount of fluctuation in the charging rate of the lithium-ion battery when the lithium-ion battery is left alone for a predetermined period of time at a predetermined charging rate, based on the derived SOC-OCV characteristic, and may derive as the threshold a voltage fluctuated by the derived allowable fluctuation amount from a measured value of the open-circuit voltage of the lithium-ion battery before it is left alone for the predetermined period of time at a predetermined charging rate.

[0019] The determination unit may determine a measured value of an open circuit voltage of the lithium ion battery after the lithium ion battery is left at a predetermined charge rate for a predetermined period of time, using the derived threshold value. Effect of the Invention

[0020] According to the disclosed technology, when determining whether an object is good or bad using a threshold value set for each object to be inspected, it is possible to prevent the inspection time from becoming too long. [Brief description of the drawings]

[0021] [Figure 1] FIG. 2 is a diagram illustrating an example of a functional configuration of an inspection apparatus according to an embodiment of the disclosed technique. [Diagram 2] FIG. 1 is a diagram showing an example of a V-dQ / dV characteristic. [Diagram 3]FIG. 13 is a diagram showing the relationship between predicted and actually measured values ​​of initial capacitance deviation. [Figure 4A] FIG. 1 is a diagram showing an example of SOV-OCV characteristics of a lithium ion battery. [Figure 4B] This is an enlarged view of the area enclosed by the square in FIG. 4A. [Figure 5A] FIG. 4 is a diagram showing an example of the relationship between positive electrode capacity and SOC deviation amount. [Figure 5B] FIG. 11 is a diagram showing an example of the relationship between the initial capacitance deviation amount and the SOC deviation amount. [Figure 6] 10 is a flowchart showing an example of a process flow in a self-discharge inspection. [Figure 7] 11 is a diagram for explaining a method for deriving a threshold value by a threshold value deriving unit; FIG. [Figure 8] 4 is a flowchart showing an example of the flow of an inspection process performed by an inspection device. [Figure 9] 1 is a flowchart showing an example of a flow of an inspection process performed by an inspection device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, an example of an embodiment of the disclosed technology will be described with reference to the drawings. In each drawing, the same or equivalent components and parts are given the same reference numerals, and duplicated descriptions will be omitted.

[0023] [First embodiment] 1 is a diagram showing an example of a functional configuration of an inspection device 10 according to an embodiment of the disclosed technique. The inspection device 10 has a determination function in a self-discharge inspection of a lithium-ion battery. The inspection device 10 is installed, for example, in a manufacturing line for lithium-ion batteries.

[0024] The inspection device 10 has an acquisition unit 11, an extraction unit 12, a first calculation unit 13, a second calculation unit 14, a characteristic derivation unit 15, a threshold derivation unit 16, a judgment unit 17, and a storage unit 18. The inspection device 10 is equipped with a computer (not shown). The computer functions as the acquisition unit 11, the extraction unit 12, the first calculation unit 13, the second calculation unit 14, the characteristic derivation unit 15, the threshold derivation unit 16, and the judgment unit 17 by executing an inspection program. The storage unit 18 is realized by a non-volatile storage medium such as a hard disk and a semiconductor memory provided in the inspection device 10. Each of the above-mentioned functional units constituting the inspection device 10 will be described in detail below.

[0025] The acquisition unit 11 acquires a V-dQ / dV characteristic indicating the relationship between the battery voltage V and dQ / dV at the time of the initial charging of the lithium ion battery to be inspected. dQ / dV is the ratio of the change amount dQ of the charge charge to the change amount dV of the battery voltage at the time of charging the lithium ion battery. The V-dQ / dV characteristic is a graph in which the horizontal axis represents the battery voltage V and the vertical axis represents dQ / dV, and the transition of the relationship between the battery voltage V and dQ / dV at the time of charging the lithium ion battery is plotted. FIG. 2 is a diagram showing an example of the V-dQ / dV characteristic. FIG. 2 illustrates an example of the V-dQ / dV characteristic acquired for each of the four lithium ion batteries [1] to [4]. The lithium ion batteries [1] to [4] have the following configurations. Positive electrode: Lithium nickel cobalt manganese oxide (Li(NiCoMn)O4) Negative electrode: Natural graphite Electrolyte: organic solvent (EC, DMC, EMC), Li salt (LiPF6), additives (LiBOB, FSO3Li, LiPO2F2)

[0026] The extraction unit 12 extracts a first dQ / dV value X1 and a second dQ / dV value X2 from the V-dQ / dV characteristic acquired by the acquisition unit 11. The first dQ / dV value X1 and the second dQ / dV value X2 are dQ / dV values ​​of a portion where a characteristic shape appears in the V-dQ / dV characteristic.

[0027] The first dQ / dV value X1 is a dQ / dV value of a characteristic portion that appears in the V-dQ / dV characteristic due to a coating formed on the negative electrode of the lithium-ion battery, which is derived from an additive contained in the electrolyte of the lithium-ion battery to be inspected. During the initial charging of the lithium-ion battery, a coating derived from an additive added to the electrolyte is formed on the negative electrode of the lithium-ion battery. It is known that the coating formed from the additive enhances the life performance of the lithium-ion battery. The first dQ / dV value X1 is a dQ / dV value of a characteristic portion that is caused by a coating that enhances the life performance of the lithium-ion battery. When this coating is formed, a peak is formed in the V-dQ / dV characteristic near a battery voltage of 1.8V. The extraction unit 12 extracts, for example, a dQ / dV value when the battery voltage is 1.8V as the first dQ / dV value X1. Examples of additives that have the effect of improving the life performance of lithium-ion batteries include LiBOB (lithium bis(oxalatoborate), 1,3-divinyltetramethyldisiloxane, 1,3-bis(isocyanatomethyl)cyclohexane, etc. The battery voltage corresponding to the first dQ / dV value X1 is not limited to 1.8 V, and can be changed appropriately depending on the components of the additive used, etc.

[0028] The second dQ / dV value X2 is a dQ / dV value of a characteristic portion that appears in the V-dQ / dV characteristic due to a coating formed on the negative electrode of the lithium ion battery, which is derived from an organic solvent contained in the electrolyte of the lithium ion battery to be inspected. During the initial charging of the lithium ion battery, a coating derived from an organic solvent contained in the electrolyte is formed on the negative electrode of the lithium ion battery. It is known that the coating formed from the organic solvent reduces the life performance of the lithium ion battery. The second dQ / dV value X2 is a dQ / dV value of a characteristic portion that is caused by a coating that reduces the life performance of the lithium ion battery. When this coating is formed, a portion in which the slope changes is formed near a battery voltage of 2.7V in the V-dQ / dV characteristic. The extraction unit 12 extracts, for example, a dQ / dV value when the battery voltage is 2.7V as the second dQ / dV value X2. Examples of organic solvents that reduce the life performance of lithium-ion batteries include EC (ethylene carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), etc. The battery voltage corresponding to the second dQ / dV value X2 is not limited to 2.7 V, but can be changed appropriately depending on the components of the organic solvent used.

[0029] The first calculation unit 13 calculates a predicted value ΔQ of the deviation ΔQ of the initial capacity of the lithium ion battery from the reference value based on the first dQ / dV value X1 and the second dQ / dV value X2 extracted by the extraction unit 12. e The initial capacity is the capacity of the lithium-ion battery after the initial charging process and the aging process. The reference value of the initial capacity is Q s , the initial capacity of the lithium-ion battery under test is Q a Then, the deviation ΔQ of the initial capacity of the lithium ion battery from the reference value (hereinafter referred to as the initial capacity deviation ΔQ) is expressed by the following formula (1). ΔQ=Q a -Q s (1)

[0030] Reference value Q s is a theoretical value determined by the design of the lithium-ion battery. Let the initial capacity of the lithium-ion battery under test be Qa can be obtained by measurement, but the inspection device 10 according to the present embodiment can obtain Q a The first calculation unit 13 calculates the predicted value ΔQ of the initial capacitance deviation ΔQ by using the first prediction formula 21 stored in the storage unit 18. e Calculate 。

[0031] The first prediction formula 21 includes the first dQ / dV value X1 and the second dQ / dV value X2 as variables. The first prediction formula 21 can be expressed by the following formula (2). The first calculation unit 13 substitutes the first dQ / dV value X1 and the second dQ / dV value X2 extracted by the extraction unit 12 into the first prediction formula 21 exemplified by formula (2) to calculate a predicted value ΔQ e In equation (2), a and b are coefficients, and c is a constant. ΔQ e = aX1 + bX2 + c (2)

[0032] The first prediction formula 21 is derived by obtaining the first dQ / dV value X1, the second dQ / dV value X2, and the initial capacity deviation ΔQ at the time of initial charging for each of a plurality of lithium ion batteries by actual measurement, and performing a multiple regression analysis on these obtained values ​​with X1 and X2 as explanatory variables and ΔQ as a response variable to determine the coefficients a, b, and constant c in formula (2).

[0033] As the first prediction formula 21, for example, the following (3) is used to obtain the predicted value ΔQ e It is possible to calculate ΔQ e =-0.041X1+0.015X2+0.007...(3)

[0034] Figure 3 shows the predicted value ΔQ calculated using equation (3). e 1 is a diagram showing the relationship between the initial capacitance deviation amount ΔQ and the actual measured value ΔQ. e The coefficient of determination R indicates the degree of agreement between the measured value and the 2was 0.9202, and the two results were almost the same.

[0035] The second calculation unit 14 calculates a predicted value ΔS of a deviation amount ΔS from a reference value in the SOC-OCV characteristic of the lithium ion battery to be inspected (hereinafter referred to as SOC deviation amount ΔS). e The SOC-OCV characteristic is a characteristic that indicates the relationship between the state of charge (SOC) and the open circuit voltage (OCV).

[0036] Fig. 4A is a diagram showing an example of the SOV-OCV characteristics of a lithium-ion battery. Fig. 4B is an enlarged view of the area enclosed by a square in Fig. 4A. In Fig. 4A and Fig. 4B, the dotted lines show the SOV-OCV characteristics of the reference battery, and the solid lines show the SOV-OCV characteristics of the test battery.

[0037] The charging rate of the reference battery is set to the reference value S s The reference value S of the reference battery s The charge rate of the test battery corresponding to the open circuit voltage equal to the open circuit voltage corresponding to S a Then, the SOC deviation amount ΔS is expressed by the following equation (3). ΔS=S a -S s (3)

[0038] The second calculation unit 14 uses the second prediction formula 22 stored in the storage unit 18 to calculate a predicted value ΔS of the SOC deviation ΔS for the lithium ion battery to be inspected. e Here, the SOC deviation amount ΔS is a value specified at each point in the range of the charging rate from 0% to 100%. For example, in FIG. 4B, s The SOC deviation ΔS when the charging rate (reference value S s ) is changed in increments of 1%, for example, and the predicted value ΔS of the SOC deviation ΔS is calculated. e The storage unit 18 stores the charging rate (reference value S sA plurality of second prediction formulas 22 corresponding to the cases where the charging rate (reference value S s ) Predicted value ΔS of the SOC deviation ΔS corresponding to e In calculating the above, the corresponding second prediction formula 22 is used.

[0039] The second prediction formula 22 is the initial capacity deviation ΔQ and the positive electrode capacity C of the lithium ion battery to be tested. a The second prediction formula 22 can be expressed by the following formula (4). The second calculation unit 13 applies the predicted value ΔQ of the initial capacitance deviation amount ΔQ calculated by the first calculation unit 13 to the second prediction formula 22 exemplified by formula (4). e and positive electrode capacity C a By substituting the above, the predicted value of the SOC deviation ΔS is e The charging rate (reference value S s In formula (4), m and n are coefficients. ΔS e =mΔQ+nC a (4)

[0040] Positive electrode capacity C a can be calculated using material and process data obtained for the lithium ion battery. a can be calculated, for example, by using the following formula (5). In formula (5), f is the Li / Me ratio, g is the Ni amount, h is the positive electrode BET, o is the positive electrode basis weight, p is the positive electrode coating width, and r is the electrode length. f, g, and h are material data, and o, p, and r are process data. Positive electrode capacity C a is calculated for each production lot of the lithium ion battery, for example, and is stored in the memory unit 18 as the positive electrode capacity data 23. C a =(-143f+4.5g+1.1h+226.4)×o×p×r ···(5)

[0041] The second prediction formula 22 is a prediction formula for each of a plurality of lithium ion batteries, which is obtained by calculating the SOC deviation amount ΔS, the initial capacity deviation amount ΔQ, and the positive electrode capacity C aand for these values, ΔQ and C a It is derived by performing multiple regression analysis with the explanatory variables and the SOC deviation ΔS as the response variable to determine the coefficients m and n in equation (4).

[0042] Here, FIG. 5A shows the positive electrode capacity C a 5A is a graph showing an example of the relationship between the positive electrode capacity C and the SOC deviation amount ΔS (when the charging rate is 60%). a and the SOC deviation amount ΔS are in a proportional relationship. On the other hand, FIG. 5B is a diagram showing an example of the relationship between the initial capacity deviation amount ΔQ and the SOC deviation amount ΔS (when the charging rate is 60%). As shown in FIG. 5B, the initial capacity deviation amount ΔQ and the SOC deviation amount ΔS are in a proportional relationship. These facts are related to the initial capacity deviation amount ΔQ and the positive electrode capacity C a functions effectively as an explanatory variable, and the SOC deviation amount ΔS functions effectively as a response variable, thereby demonstrating the validity of the second prediction formula 22 represented by formula (4).

[0043] The characteristic deriving unit 15 calculates the predicted value ΔS of the SOC deviation ΔS calculated by the second calculation unit 14. e Specifically, the characteristic deriving unit 15 calculates the charging rate in the SOC-OCV characteristic of a known reference battery by multiplying the predicted value ΔS e The SOC-OCV characteristics of the lithium-ion battery under test are derived by shifting the SOC-OCV characteristics by an amount equivalent to the above.

[0044] The threshold derivation unit 16 determines a threshold V for determining the open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charge rate for a predetermined period of time based on the SOC-OCV characteristics of the lithium ion battery to be inspected derived by the characteristic derivation unit 15. th1 Derive.

[0045] In the manufacturing process of lithium-ion batteries, a self-discharge test is carried out to screen out lithium-ion batteries with micro-short circuits as non-conforming products. In the self-discharge test, a threshold V is set for the open-circuit voltage of a lithium-ion battery when the battery is left at a certain charge rate for a certain period of time. th1 The judgment is made using the following:

[0046] FIG. 6 is a flow chart showing an example of a process flow in a self-discharge inspection. In step P1, an initial charge is performed on the lithium ion battery to be inspected. In the initial charge, the lithium ion battery is charged until the charging rate reaches, for example, 100%. In step P2, the lithium ion battery to be inspected is aged. This is performed to dissolve and remove foreign matter such as metal that was mixed into the lithium ion battery during manufacture. In addition, by performing aging, the movement state of the lithium ions moving the electrolyte is stabilized. In step P3, an initial discharge is performed on the lithium ion battery to be inspected. In the initial charge, the lithium ion battery is discharged until the charging rate reaches, for example, 0%. In step P4, the lithium ion battery to be inspected is charged until the charging rate reaches, for example, 20%, and the open voltage V1 of the lithium ion battery at that time is measured. In step P5, the lithium ion battery to be inspected is left for, for example, 24 hours. In step P6, the open voltage V2 of the lithium ion battery is measured. The open voltages V1 and V2 are stored in the memory unit 18 as measurement data 24.

[0047] In this embodiment, the threshold derivation unit 16 calculates a threshold value V for determining a differential voltage ΔV (=V1−V2) between an open-circuit voltage V1 before being left unused measured in step P4 and an open-circuit voltage V2 after being left unused measured in step P6. th1 Derive.

[0048] FIG. 7 shows the threshold V th1The threshold derivation unit 16 calculates the open-circuit voltage V of the lithium-ion battery when the charging rate changes to the limit allowed as the amount of fluctuation in the charging rate when the lithium-ion battery is left for 24 hours at a charging rate (e.g., 20%) corresponding to the open-circuit voltage V1, based on the SOC-OCV characteristic of the lithium-ion battery under test derived by the characteristic derivation unit 15. LIM The threshold derivation unit 16 derives V1 to V LIM The threshold value V is used to determine the amount of change in the open circuit voltage up to the differential voltage ΔV. th1 Issue it as.

[0049] The determination unit 17 determines the threshold value V th1 Specifically, the determination unit 17 acquires an open circuit voltage V1 before the device is left unused, which is measured in step P4, and an open circuit voltage V2 after the device is left unused, which is measured in step P6. The determination unit 17 derives a differential voltage ΔV (=V1-V2), which is the difference between V1 and V2. The determination unit 17 determines whether the differential voltage ΔV is greater than or equal to a threshold value V th1 If the difference voltage ΔV is smaller than the threshold V, the lithium-ion battery is judged as pass. th1 If the test result is equal to or greater than this, the lithium ion battery is determined to be unqualified.

[0050] 8 is a flowchart showing an example of the flow of the lithium ion battery inspection process performed by the inspection device 10. In step S1, the acquisition unit 11 acquires a V-dQ / dV curve as shown in FIG.

[0051] In step S2, the extraction unit 12 extracts a first dQ / dV value X1 and a second dQ / dV value X2 from the V-dQ / dV curve acquired in step S1. In this embodiment, the extraction unit 12 extracts the dQ / dV value when the battery voltage is 1.8 V as the first dQ / dV value X1, and extracts the dQ / dV value when the battery voltage is 2.7 V as the second dQ / dV value X2.

[0052] In step S3, the first calculation unit 13 substitutes the first dQ / dV value X1 and the second dQ / dV value X2 extracted in step S2 into the first prediction formula 21 to calculate a predicted value ΔQ of the initial capacity deviation amount ΔQ of the lithium ion battery to be inspected. e Calculate.

[0053] In step S4, the second calculation unit 13 inputs the predicted value ΔQ calculated in step S3 into the second prediction formula 22. e and positive electrode capacity C a By substituting the above, the predicted value ΔS of the SOC deviation ΔS of the lithium-ion battery under test is obtained. e The second calculation unit 14 calculates the charging rate (reference value S s ) For each prediction value ΔS e Calculate.

[0054] In step S5, the characteristic deriving unit 15 calculates the predicted value ΔS e Specifically, the characteristic deriving unit 15 derives the SOC-OCV characteristic of the lithium ion battery under test based on the predicted value ΔS calculated in step S4. e The SOC-OCV characteristics of the lithium-ion battery under test are derived by shifting the SOC-OCV characteristics by an amount equivalent to the above.

[0055] In step S6, the threshold derivation unit 16 determines a threshold V for determining the open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charge rate for a predetermined period of time based on the SOC-OCV characteristics of the lithium ion battery to be inspected derived in step S5. th1 Specifically, the threshold derivation unit 16 derives the open circuit voltage V of the lithium ion battery when the charging rate of the lithium ion battery changes to the limit allowed as the amount of fluctuation in the charging rate when the lithium ion battery is left for a predetermined period of time at a charging rate (e.g., 20%) corresponding to the open circuit voltage V1, based on the SOC-OCV characteristics of the lithium ion battery to be inspected. LIM The threshold derivation unit 16 derives V1 to V LIMThe threshold value V is used to determine the amount of change in the open circuit voltage up to the differential voltage ΔV. th1 It is derived as:

[0056] In step S7, the determination unit 17 reads out from the storage unit 18 and acquires the open-circuit voltage V1 before being left unused, measured in step P4, and the open-circuit voltage V2 after being left unused, measured in step P6.

[0057] In step S8, the determination unit 17 derives a differential voltage ΔV (=V1−V2) which is the difference between V1 and V2 acquired in step S7.

[0058] In step S9, the determination unit 17 determines whether the differential voltage ΔV derived in step S8 is equal to or smaller than the threshold value V derived in step S6. th1 The determination unit 17 determines whether the differential voltage ΔV is smaller than the threshold value V th1 If it is determined that the difference voltage ΔV is smaller than the threshold value V, the lithium ion battery is determined to be acceptable in step S10. th1 If it is determined that the battery is equal to or greater than this, the lithium ion battery is determined to be a failure in step S11.

[0059] According to the inspection device 10 according to the embodiment of the disclosed technique, a threshold value V is set to determine a difference voltage ΔV between an open circuit voltage V1 before being left unused and an open circuit voltage V2 after being left unused, which are obtained in a self-discharge inspection. th1 is set for each individual to be inspected, it is possible to prevent losses caused by rejecting what should have been a pass. th1 In order to derive the threshold value V, it is not necessary to measure the capacity of the lithium ion battery to be inspected. That is, according to the inspection device 10 according to the embodiment of the disclosed technique, the threshold value V th1 When the quality determination is performed using the above method, it is possible to prevent the inspection time from becoming too long.

[0060] [Second embodiment] The inspection device 10 according to the first embodiment described above uses a threshold value V for judging the differential voltage ΔV as a threshold value for judging the open circuit voltage of a lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time. th1 The aim of this study was to derive the following:

[0061] In contrast, the inspection device 10 according to the second embodiment uses a threshold value V th2 Derive.

[0062] Fig. 9 is a flowchart showing an example of the flow of the lithium ion battery inspection process performed by the inspection device 10 according to the second embodiment. Note that each process from step S1 to step S5 in the flowchart shown in Fig. 9 is the same as that in the flowchart according to the first embodiment shown in Fig. 8, and therefore a description thereof will be omitted.

[0063] In step S12, based on the SOC-OCV characteristics of the lithium-ion battery being tested derived in step S5, the threshold derivation unit 16 derives an allowable fluctuation amount, which is the amount of fluctuation in the open circuit voltage of the lithium-ion battery when the charging rate changes to the limit allowable as the amount of fluctuation in the charging rate of the lithium-ion battery when the lithium-ion battery at a specified charging rate is left for a specified period of time.

[0064] In step S13, the threshold derivation unit 16 reads out from the storage unit 18 the open circuit voltage V1 before the device was left unused, which was measured in step P4.

[0065] In step S14, the threshold derivation unit 16 determines a threshold V for determining the open-circuit voltage V2 after being left unused by varying the open-circuit voltage V1 obtained in step S13 by the allowable variation amount derived in step S12. th2 It is derived as:

[0066] In step S15, the determination unit 17 reads out from the storage unit 18 the open circuit voltage V2 after the storage voltage V2 was measured in process P6.

[0067] In step S16, the determination unit 17 determines whether the open-circuit voltage V2 after being left unused obtained in step S15 is greater than or equal to the threshold voltage V th2 The determination unit 17 determines whether the open circuit voltage V2 is equal to or greater than the threshold value V th2 If it is determined that the open circuit voltage V2 is equal to or greater than the threshold voltage V, the lithium ion battery is determined to be acceptable in step S17. th2 If it is determined that the battery is less than the specified level, the lithium ion battery is determined to be a failure in step S18.

[0068] According to the inspection device 10 according to the second embodiment of the disclosed technique, a threshold value V th2 When the quality determination is performed using the above method, it is possible to prevent the inspection time from becoming too long.

[0069] The following supplementary notes are further disclosed regarding the above first and second embodiments. (Appendix 1) A method for testing a lithium ion battery, comprising the steps of: acquiring a V-dQ / dV characteristic indicating a relationship between an inter-electrode voltage and dQ / dV during an initial charge of the lithium ion battery; extracting a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; a prediction formula for calculating a first predicted value, which is a predicted value of a deviation amount of an initial capacity of the lithium ion battery from a reference value, the first predicted value being calculated by substituting the extracted first dQ / dV value and the second dQ / dV value into a first prediction formula including the first dQ / dV value and the second dQ / dV value as variables; a prediction formula for calculating a second predicted value, which is a predicted value of a deviation amount from a reference value in an SOC-OCV characteristic that indicates a relationship between a charging rate and an open circuit voltage of the lithium ion battery, the second predicted value being calculated by substituting the calculated first predicted value into the second prediction formula that includes, as a variable, a deviation amount of an initial capacity of the lithium ion battery from a reference value; Deriving an SOC-OCV characteristic of the lithium ion battery based on the calculated second predicted value; deriving a threshold value for determining an open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charge rate for a predetermined period of time based on the derived SOC-OCV characteristic; making the determination using the derived threshold value; the first dQ / dV value is a dQ / dV value of a characteristic portion appearing on the V-dQ / dV curve due to a coating formed on the negative electrode of the lithium ion battery, the coating being derived from an additive contained in an electrolyte of the lithium ion battery; The second dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from an organic solvent contained in the electrolyte of the lithium ion battery. Testing method.

[0070] (Appendix 2) The first dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from LiBOB contained in the electrolyte of the lithium ion battery. The test method described in Appendix 1.

[0071] (Appendix 3) The second dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from EC contained in the electrolyte of the lithium ion battery. 2. The method of claim 1 ,

[0072] (Appendix 4) The second predicted value further includes a positive electrode capacity of the lithium ion battery as a variable, The second predicted value is calculated by substituting the positive electrode capacity and the first predicted value into the second prediction formula. 1. The method of any one of claims 1 to 3.

[0073] (Appendix 5) deriving, as the threshold value, an allowable fluctuation amount, which is an amount of fluctuation in the open circuit voltage of the lithium ion battery when the charging rate changes to a limit allowable as an amount of fluctuation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; The lithium ion battery is stored in a predetermined state of charge for a predetermined period of time. A difference voltage between before and after the open circuit voltage of the lithium ion battery is determined using the derived threshold value. 1. The testing method according to any one of appendix 1 to appendix 4.

[0074] (Appendix 6) deriving an allowable variation amount, which is an amount of variation in an open circuit voltage of the lithium ion battery when a charging rate of the lithium ion battery changes to a limit allowable as an amount of variation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; deriving, as the threshold value, a voltage that is fluctuated by the derived allowable fluctuation amount from a measured open circuit voltage of the lithium ion battery before the lithium ion battery is left unused for a predetermined period of time while the lithium ion battery is at a predetermined charge rate; The lithium ion battery is stored in a predetermined state of charge for a predetermined period of time. A measured value of an open circuit voltage of the lithium ion battery after the lithium ion battery is left in the storage state is determined using the derived threshold value. 5. The method of any one of claims 1 to 4.

[0075] (Appendix 7) A lithium ion battery inspection device, An acquisition unit that acquires a V-dQ / dV characteristic that indicates a relationship between an inter-electrode voltage and dQ / dV during an initial charge of the lithium ion battery; an extracting unit that extracts a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; a first calculation unit that calculates a first predicted value, which is a predicted value of a deviation amount of an initial capacity of the lithium ion battery from a reference value, by substituting the extracted first dQ / dV value and the extracted second dQ / dV value into a first prediction formula including the first dQ / dV value and the second dQ / dV value as variables; a second calculation unit that calculates a second predicted value by substituting the calculated first predicted value into a prediction formula for calculating a second predicted value, which is a predicted value of a deviation amount from a reference value in a SOC-OCV characteristic that indicates a relationship between a charging rate and an open circuit voltage of the lithium ion battery, the second prediction formula including a deviation amount of an initial capacity of the lithium ion battery from a reference value as a variable; a characteristic deriving unit that derives an SOC-OCV characteristic of the lithium ion battery based on the calculated second predicted value; a threshold derivation unit that derives a threshold for determining an open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charge rate for a predetermined period of time based on the derived SOC-OCV characteristic; a determination unit that performs the determination using the derived threshold value, the first dQ / dV value is a dQ / dV value of a characteristic portion appearing on the V-dQ / dV curve due to a coating formed on the negative electrode of the lithium ion battery, the coating being derived from an additive contained in an electrolyte of the lithium ion battery; The second dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from an organic solvent contained in the electrolyte of the lithium ion battery. Inspection equipment.

[0076] (Appendix 8) the threshold derivation unit derives, as the threshold, an amount of change in open circuit voltage of the lithium ion battery when the charging rate changes to a limit allowable as an amount of change in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; The determination unit determines a differential voltage, which is a difference between an open-circuit voltage of the lithium ion battery before and after the lithium ion battery is left at a predetermined charging rate for a predetermined period of time, using the derived threshold value. 8. The inspection device according to claim 7.

[0077] (Appendix 9) The threshold derivation unit deriving an allowable variation amount, which is an amount of variation in an open circuit voltage of the lithium ion battery when a charging rate of the lithium ion battery changes to a limit allowable as an amount of variation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; deriving, as the threshold value, a voltage that is fluctuated by the derived allowable fluctuation amount from a measured open circuit voltage of the lithium ion battery before the lithium ion battery is left unused for a predetermined period of time while the lithium ion battery is at a predetermined charge rate; The determination unit determines a measured value of an open circuit voltage of the lithium ion battery after the lithium ion battery is left at a predetermined charge rate for a predetermined period of time, using the derived threshold value. 8. The inspection device according to claim 7. [Explanation of symbols]

[0078] 10 Inspection equipment 11 Acquisition Department 12 Extraction part 13 First calculation section 14 Second calculation section 15 Characteristics Derivation Section 16 Threshold Derivation Part 17 Judgment section 18 Storage section 21 First prediction equation 22 Second prediction formula

Claims

1. A method for testing a lithium ion battery, comprising: A V-dQ / dV characteristic showing the relationship between the interelectrode voltage and dQ / dV during the initial charge of the lithium ion battery is obtained; extracting a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; a prediction formula for calculating a first predicted value, which is a predicted value of a deviation amount of an initial capacity of the lithium ion battery from a reference value, the first predicted value being calculated by substituting the extracted first dQ / dV value and the second dQ / dV value into a first prediction formula including the first dQ / dV value and the second dQ / dV value as variables; a prediction formula for calculating a second predicted value, which is a predicted value of a deviation amount from a reference value in an SOC-OCV characteristic indicating a relationship between a charging rate and an open circuit voltage of the lithium ion battery, the second predicted value being calculated by substituting the calculated first predicted value into a second prediction formula including, as a variable, a deviation amount of an initial capacity of the lithium ion battery from a reference value; Deriving an SOC-OCV characteristic of the lithium ion battery based on the calculated second predicted value; Deriving a threshold value for determining an open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charge rate for a predetermined period of time based on the derived SOC-OCV characteristic; making the determination using the derived threshold value; the first dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode of the lithium ion battery, the coating being derived from an additive contained in an electrolyte of the lithium ion battery; The second dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from an organic solvent contained in the electrolyte of the lithium ion battery. Testing method.

2. The first dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from LiBOB contained in the electrolyte of the lithium ion battery. The inspection method according to claim 1 .

3. The second dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from EC contained in the electrolyte of the lithium ion battery. The inspection method according to claim 1 .

4. The second predicted value further includes a positive electrode capacity of the lithium ion battery as a variable, The second predicted value is calculated by substituting the positive electrode capacity and the first predicted value into the second prediction formula. The inspection method according to claim 1 .

5. deriving, as the threshold value, an allowable fluctuation amount which is an amount of fluctuation in an open circuit voltage of the lithium ion battery when a charging rate changes to a limit allowable as an amount of fluctuation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; The lithium ion battery is stored in a predetermined state of charge for a predetermined period of time. A difference voltage between before and after the open circuit voltage of the lithium ion battery is determined using the derived threshold value. The inspection method according to claim 1 .

6. deriving an allowable fluctuation amount, which is an amount of fluctuation in an open circuit voltage of the lithium ion battery when a charging rate changes to a limit allowable as an amount of fluctuation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; deriving, as the threshold value, a voltage that is fluctuated by the derived allowable fluctuation amount from a measured open circuit voltage of the lithium ion battery before the lithium ion battery is left unused for a predetermined period of time while the lithium ion battery is at a predetermined charge rate; The lithium ion battery is stored in a predetermined state of charge for a predetermined period of time. A measured value of an open circuit voltage of the lithium ion battery after the lithium ion battery is left in the storage state is determined using the derived threshold value. The inspection method according to claim 1 .

7. A lithium ion battery inspection device, An acquisition unit that acquires a V-dQ / dV characteristic that indicates a relationship between an inter-electrode voltage and dQ / dV during an initial charge of the lithium ion battery; an extraction unit that extracts a first dQ / dV value and a second dQ / dV value from the V-dQ / dV characteristic; a first calculation unit that calculates a first predicted value, which is a predicted value of a deviation amount of an initial capacity of the lithium ion battery from a reference value, by substituting the extracted first dQ / dV value and the extracted second dQ / dV value into a first prediction formula including the first dQ / dV value and the extracted second dQ / dV value as variables; a second calculation unit that calculates a second predicted value by substituting the calculated first predicted value into a prediction formula for calculating a second predicted value, the second predicted value being a predicted value of a deviation from a reference value in an SOC-OCV characteristic indicating a relationship between a charging rate and an open circuit voltage of the lithium ion battery, the second prediction formula including a deviation from a reference value of an initial capacity of the lithium ion battery as a variable; a characteristic deriving unit that derives an SOC-OCV characteristic of the lithium ion battery based on the calculated second predicted value; a threshold derivation unit that derives a threshold for determining an open circuit voltage of the lithium ion battery when the lithium ion battery is left at a predetermined charge rate for a predetermined period of time based on the derived SOC-OCV characteristic; a determination unit that performs the determination using the derived threshold value, the first dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode of the lithium ion battery, the coating being derived from an additive contained in an electrolyte of the lithium ion battery; The second dQ / dV value is a dQ / dV value of a characteristic portion that appears on the V-dQ / dV curve due to a coating formed on the negative electrode, the coating being derived from an organic solvent contained in the electrolyte of the lithium ion battery. Inspection equipment.

8. the threshold derivation unit derives, as the threshold, an amount of fluctuation in an open circuit voltage of the lithium ion battery when a charging rate changes to a limit permitted as an amount of fluctuation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; The determination unit determines a differential voltage, which is a difference between an open-circuit voltage of the lithium ion battery before and after the lithium ion battery is left at a predetermined charging rate for a predetermined period of time, using the derived threshold value.

8. The inspection apparatus according to claim 7.

9. The threshold derivation unit deriving an allowable fluctuation amount, which is an amount of fluctuation in an open circuit voltage of the lithium ion battery when a charging rate changes to a limit allowable as an amount of fluctuation in the charging rate of the lithium ion battery when the lithium ion battery is left at a predetermined charging rate for a predetermined period of time based on the derived SOC-OCV characteristic; deriving, as the threshold value, a voltage that is fluctuated by the derived allowable fluctuation amount from a measured open circuit voltage of the lithium ion battery before the lithium ion battery is left unused for a predetermined period of time while the lithium ion battery is at a predetermined charge rate; The determination unit determines a measured value of an open circuit voltage of the lithium ion battery after the lithium ion battery is left at a predetermined charge rate for a predetermined period of time, using the derived threshold value.

8. The inspection apparatus according to claim 7.

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