JP2014006205A - Secondary battery inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery inspection method configured to detect micro-short circuit in a battery in a short time easily with high accuracy.SOLUTION: A secondary battery inspection method includes: a first voltage drop measurement process that adjusts a secondary battery 1 to an arbitrary SCO and measures voltage decreased during aging processing; a second voltage drop measurement process which is repeated a plurality of times, charges the secondary battery 1 only with an arbitrary amount of current to adjust the SOC to be different from the SOC which has been set for past voltage drop measurement to measure the voltage drop during the aging processing; a first estimation process that calculates a first estimated SOC from the voltage drop in the first voltage drop measurement process and a reference line; a second estimation process that adjusts the first estimated SOC with the amount of current in the second voltage drop measurement process to calculate a second estimated SOC; and a determination process that compares an actual measurement line showing a relation between the voltage drops in the voltage drop measurement processes and the first and second estimated SOCs with the reference line to determine a micro-short circuit.

Description

  The present invention relates to a secondary battery inspection method for detecting a minute short circuit between a positive electrode and a negative electrode in a secondary battery.

Conventionally, in a secondary battery such as a lithium ion secondary battery, a positive electrode, a negative electrode, and a separator are stacked so that a separator is interposed between the positive electrode and the negative electrode to form an electrode body. .
When metal impurities or the like are mixed on the positive electrode side of the electrode body, the metal impurities or the like that are in contact with the electrolytic solution are dissolved and reach the negative electrode, and are deposited on the negative electrode surface to form a micro short circuit between the positive and negative electrodes (micro short). May occur.

And as a method of inspecting the micro short circuit between the positive and negative electrodes generated in the secondary battery, for example, there is a detection method described in Patent Document 1.
Specifically, the detection method described in Patent Literature 1 includes a charging step of charging a secondary battery up to a first SOC (state of charge), and the secondary battery is left for a predetermined time after the charging step. A leaving step, a discharging step for discharging to a second SOC lower than the first SOC after the leaving step, and after the discharging step, setting the secondary battery to a battery temperature lower than a predetermined temperature, A detection step of detecting a minute short circuit of the secondary battery is provided.
In the detection step, the secondary battery is allowed to stand for a predetermined time at the low battery temperature to perform an aging process, and a voltage drop that is a voltage change amount with respect to the predetermined time during the aging process is measured. Further, the measured voltage drop degree and the reference voltage drop degree are compared, and if the voltage drop degree is higher than the reference voltage drop degree, it is determined that a micro short-circuit has occurred.

JP 2011-69775 A

  When a small short circuit is detected by comparing the voltage drop degree and the reference voltage drop degree in the detection method described above, the secondary battery, particularly the high-capacity type secondary battery cell, is internally connected between solids or lots. When there is a variation in resistance, it is difficult to distinguish between a change in the voltage drop due to a very small short circuit and a change in the voltage drop due to a variation in internal resistance, and a very small short circuit cannot be detected There is.

Further, when detecting a short-circuit of the secondary battery, if the voltage drop degree is measured at a low battery temperature (for example, −30 ° C.) as described above, the amount of self-discharge of the secondary battery itself is reduced. There is an advantage that it becomes easy to detect a difference in voltage drop due to the presence or absence of a short circuit.
However, by lowering the temperature of the secondary battery, the cell surface freezes and moisture tends to enter the battery, causing a decrease in capacity and an increase in internal resistance, or measuring the voltage drop at a low temperature. There is a problem that special equipment and process management are required, and the process of detecting a micro short circuit becomes complicated.

Furthermore, when detecting a short-circuit of the secondary battery, in the region where the SOC of the secondary battery is low, the change in the voltage drop with respect to the SOC variation is large (the OCV curve indicating the change in OCV (open circuit voltage) due to the SOC). Therefore, the difference between the voltage drop of a secondary battery with a micro short circuit and the voltage drop of a secondary battery without a micro short circuit is likely to occur, and it is easy to detect the presence of a micro short circuit. There are advantages such as.
However, when the voltage drop degree of the secondary battery is measured in such a portion where the slope of the OCV curve is large, the voltage of the secondary battery changes greatly due to a slight change in the SOC, so the voltage drop degree is measured. The initial voltage at the time varies, and there is a problem that it takes time and labor to adjust the initial voltage.

  Therefore, in the present invention, there is provided an inspection method for a secondary battery that can detect the presence or absence of a micro short circuit inside the battery with high accuracy even in a secondary battery having a large variation in internal resistance. It is to provide.

A secondary battery inspection method that solves the above-described problems has the following characteristics.
That is, a method for inspecting a secondary battery comprising an electrode body configured by stacking a positive electrode, a negative electrode, and a separator so that the separator is interposed between the positive electrode and the negative electrode, After adjusting the secondary battery to an arbitrary SOC, an aging process is performed, and a first voltage drop amount measuring step for measuring a voltage drop amount of the secondary battery during the aging process, and the first voltage drop amount When the secondary battery is measured by measuring the amount of voltage drop up to the previous time by charging or discharging the secondary battery by an arbitrary amount of current after the measurement process. A second voltage drop amount measuring step of performing an aging process and measuring a voltage drop amount of the secondary battery at the time of the aging process, after adjusting to an SOC different from all the SOCs of the first voltage, Fall From the reference line indicating the relationship between the voltage drop amount measured in the quantity measurement step and the SOC and voltage drop amount in the model secondary battery in which it is known that there is no pre-calculated minute short circuit. A first estimation step of calculating an SOC when the voltage drop amount is measured in the first voltage drop amount measurement step in the battery as a first estimated SOC, and the plurality of the first estimated SOC Adjustment of the amount of current that has been charged or discharged in the second voltage drop measurement step, and a plurality of second estimated SOCs corresponding to the plurality of second voltage drop measurement steps. Second estimation step to be calculated, voltage drop amount measured in the first voltage drop amount measurement step and the plurality of second voltage drop amount measurement steps, and primary estimation corresponding to each voltage drop amount SOC and multiple second order estimated SOs Comparing the actual measurement line indicating the relationship with the reference line, and determining whether there is a micro short-circuit in the secondary battery according to the degree of coincidence between the actual measurement line and the reference line, A method for inspecting a secondary battery.

  Further, according to claim 2, in the determination step, whether or not there is a micro short circuit in the secondary battery according to the degree of coincidence between the actual measurement line and the reference line is determined by each of the secondary lines in the reference line. A voltage drop amount corresponding to the estimated SOC is calculated, and an average of a difference between a voltage drop amount corresponding to each secondary estimated SOC in the actual measurement line and a voltage drop amount corresponding to each secondary estimated SOC in the reference line This is done by comparing the value with a preset threshold value.

  According to a third aspect of the present invention, the SOCs when the voltage drop amount is measured in the first voltage drop amount measurement step and the plurality of second voltage drop amount measurement steps are the OCV of the secondary battery. The slope of the curve is set to a different value, and at least one of the SOCs when the voltage drop amount is measured in the first voltage drop measurement step and the plurality of second voltage drop measurement steps. Is set to a value in the range of 0-10%.

  According to the present invention, even if a secondary battery has a large variation in internal resistance, the presence or absence of a micro short circuit inside the battery can be detected with high accuracy in a short time.

It is a perspective view which shows the secondary battery used as the object of the inspection method of the secondary battery which concerns on this invention. It is the figure which showed the relationship between SOC and OCV in a secondary battery, and the SOC and voltage drop amount at the time of carrying out an aging process of a secondary battery. Reference line showing the relationship between SOC and voltage drop in model secondary battery, actual measurement line showing relationship between SOC and voltage drop when the secondary battery to be inspected is a non-defective secondary battery, and inspection It is a figure which shows the measurement line which shows the relationship between SOC and voltage drop amount when the secondary battery used as object is a micro short circuit secondary battery. It is a figure which shows the flow of the inspection method of a secondary battery. It is a figure which shows the procedure which produces the measurement line of the secondary battery used as a test object. It is a figure which shows the coincidence degree of a reference line and an actual measurement line. It is a figure which shows the voltage drop amount difference average value of a reference | standard line and an actual measurement line about each good quality sample and a micro short circuit sample. It is a figure which shows the aging process days in the conventional inspection method, and the aging process days in the inspection method of this invention.

  Next, modes for carrying out the present invention will be described with reference to the accompanying drawings.

  A secondary battery 1 that is a target of the secondary battery inspection method according to the present embodiment shown in FIG. 1 includes a bottomed rectangular tube-shaped case body 21 having an open surface (upper surface), and a flat plate-shaped case. A battery case 2 constituted by a lid body 22 that closes an opening of the main body 21 is configured by accommodating the electrode body 3 together with the electrolytic solution.

The battery case 2 is configured as a rectangular case in which an opening of a case body 21 formed in a rectangular parallelepiped bottomed rectangular tube shape with one surface (upper surface) opened is closed with a flat lid body 22. .
A positive electrode terminal 4a is provided at one end in the longitudinal direction of the lid 22 (left end in FIG. 1), and a negative electrode terminal 4b is provided at the other longitudinal end of the lid 22 (right end in FIG. 1). .

  The electrode body 3 is formed by laminating the positive electrode 31, the negative electrode 32, and the separator 33 so that the separator 33 is interposed between the positive electrode 31 and the negative electrode 32, and winding the laminated positive electrode 31, negative electrode 32, and separator 33. It is configured by flattening.

When the secondary battery 1 is configured by accommodating the electrode body 3 and the electrolyte in the battery case 2, first, the positive electrode terminal 4 a and the negative electrode terminal 4 b of the lid body 22 are respectively connected to the positive electrode 31 and the negative electrode 32 of the electrode body 3. After connecting, the electrode body 3 is assembled to the lid body 22 to form a lid body sub-assembly.
Thereafter, the electrode body 3 and the electrolytic solution are accommodated in the case main body 21, the lid body 22 is fitted into the opening of the case main body 21, and the lid body 22 and the case main body 21 are sealed by welding, A secondary battery 1 is configured.

The positive electrode 31 is made of a positive electrode mixture paste obtained by kneading an electrode material such as a positive electrode active material, a conductive material, and a binder together with a solvent. It is configured to be applied and dried and pressurized.
Similarly, the negative electrode 32 is obtained by mixing a negative electrode mixture paste obtained by kneading an electrode material such as a negative electrode active material, a thickener, and a binder with the surface (one side or both sides) of a current collector formed in a foil shape. ) And dried / pressurized.
The separator 33 is a sheet-like member made of, for example, a porous polyolefin-based resin, and is disposed between the positive electrode 31 and the negative electrode 32.

FIG. 2 shows the relationship (OCV curve) between the SOC (state of charge) and the OCV (open circuit voltage) in the secondary battery 1 and the secondary battery 1 in a predetermined environment for a predetermined time. The relationship between the SOC and the voltage drop when left standing (for example, 12 hours) (aging process) is shown.
The OCV of the secondary battery 1 increases as the SOC increases, and the slope of the OCV curve is larger in the low SOC region than in the other regions. Further, the amount of voltage drop of the secondary battery 1 varies depending on the SOC, and in a region where the SOC is low (for example, a region where the SOC is up to about 10%), it decreases as the SOC increases.

Further, in the secondary battery 1, when metal impurities or the like are mixed on the positive electrode 31 side of the electrode body 3, the metal impurities or the like that are in contact with the electrolytic solution are dissolved and reach the negative electrode 32, and are formed on the surface of the negative electrode 32. Precipitation may cause a micro short circuit between the positive and negative electrodes.
In the secondary battery 1 in which the micro short circuit has occurred, the separator 33 between the positive electrode 31 and the negative electrode 32 at the micro short circuit location has a micro conductive bridge that conducts the positive electrode 31 and the negative electrode 32, A short-circuit current flows between the positive electrode 31 and the negative electrode 32 through the conduction bridge.

Then, the amount of voltage drop in the secondary battery 1 in which the micro short-circuit has occurred is added by the amount of the short-circuit current due to the micro short-circuit compared to the secondary battery 1 in which the micro short-circuit has not occurred.
Therefore, the relationship between the SOC and the voltage drop amount, that is, the degree of change in the voltage drop amount of the secondary battery 1 due to the difference in the SOC differs depending on the presence or absence of a micro short circuit in the secondary battery 1.

  Therefore, in the inspection method of the secondary battery 1 in the present embodiment, the voltage drop amount of the secondary battery 1 is measured at a plurality of (three or more) SOCs, and the measured value and the fact that there is no micro short circuit are known. By comparing the relationship between the SOC measured in advance for the secondary battery 1 and the amount of voltage drop, the secondary battery 1 can be adjusted without taking time and effort to adjust the initial voltage during the inspection of the secondary battery 1. Is used to detect the presence or absence of a micro short circuit.

Next, the inspection method of the secondary battery 1 for detecting the presence or absence of a micro short circuit inside the battery will be specifically described.
In the inspection method of the secondary battery 1 in the present embodiment, before actually inspecting the secondary battery 1 for the presence or absence of the micro short circuit, a plurality of points in the model secondary battery that are known to have no micro short circuit are provided. A voltage drop amount is measured for the SOC, and a reference line that is a graph showing the relationship between the SOC and the voltage drop amount in the model secondary battery as shown in FIG. 3 is created in advance.

After creating the reference line, the secondary battery 1 is inspected for the presence or absence of a micro short-circuit according to the flow shown in FIG.
First, an adjustment process is performed in which the secondary battery 1 that has been initially charged is charged or discharged to adjust the secondary battery 1 to a first SOC, which is an arbitrary SOC (S11). After adjusting the secondary battery to the first SOC, an aging process is performed, and a measurement process is performed to measure the first voltage drop amount of the secondary battery 1 during the aging process (S12).

In addition, 1st SOC by which the secondary battery 1 is adjusted in adjustment process S11 is set to the value of the range of low SOC of 10% or less, for example.
In the adjustment step S11, when the secondary battery 1 is adjusted to the first SOC, it is not always necessary to strictly adjust the target SOC value, and a value in the vicinity of the target SOC value (for example, the target SOC value). It is sufficient to adjust to a value within a range of several percent centered on the SOC value.

In the measurement step S12, the voltage V1 of the secondary battery 1 before the aging process and the voltage V2 of the secondary battery 1 after the aging process are measured, and the first voltage drop ΔVA is calculated by subtracting the voltage V2 from the voltage V1. As a result, the first voltage drop amount ΔVA is measured.
The aging process is performed by leaving the secondary battery 1 for a predetermined time in an environment of a predetermined temperature.
The adjustment step S11 and the measurement step S12 constitute a first voltage drop amount measurement step S1.

Next, the secondary battery 1 that has finished the first voltage drop measurement step S1 is charged or discharged by a predetermined current amount (SOC), and the secondary battery 1 is adjusted to the second SOC. An adjustment process is performed (S21). In this case, the second SOC is adjusted so as to be different from the first SOC when the voltage drop amount is measured in the previous first voltage drop amount measurement step S1.
After the secondary battery is adjusted to the second SOC, an aging process is performed, and a measurement step of measuring a second voltage drop amount of the secondary battery 1 during the aging process is performed (S22).

In the measuring step S22, the voltage V3 of the secondary battery 1 before the aging process and the voltage V4 of the secondary battery 1 after the aging process are measured, and the second voltage drop amount ΔVB is calculated by subtracting the voltage V4 from the voltage V3. Thus, the second voltage drop amount ΔVB is measured.
In addition, the aging process in the measurement step S22 is performed by leaving the secondary battery 1 under the same conditions as in the measurement step S12.
The adjustment step S21 and the measurement step S22 constitute a first second voltage drop measurement step S2.

Next, the secondary battery 1 that has completed the first second voltage drop measurement step S2 is charged or discharged by a predetermined amount of current (SOC), and the secondary battery 1 is charged with the third SOC. An adjustment process is performed (S31). In this case, the third SOC is the total SOC when the voltage drop amount was measured in the first voltage drop measurement step S1 and the first second voltage drop measurement step S2 until the previous time (that is, Adjustment is performed so that the first SOC and the second SOC) are different from each other.
After the secondary battery is adjusted to the third SOC, an aging process is performed to measure a third voltage drop amount of the secondary battery 1 during the aging process (S32).

In the measurement step S32, the voltage V5 of the secondary battery 1 before the aging process and the voltage V6 of the secondary battery 1 after the aging process are measured, and the third voltage drop ΔVC is calculated by subtracting the voltage V6 from the voltage V5. Thus, the third voltage drop amount ΔVC is measured.
Further, the aging process in the measurement step S32 is performed by leaving the secondary battery 1 under the same conditions as in the measurement step S12.
The adjustment step S31 and the measurement step S32 constitute a second second voltage drop measurement step S3.

As described above, in the inspection method for the secondary battery 1 in the present embodiment, the second voltage drop measurement steps S2 and S3 are repeatedly performed a plurality of times.
In addition, the predetermined current amount (SOC) when the secondary battery 1 is charged or discharged in the second voltage drop measurement process S2 and S3 that is repeatedly performed a plurality of times is the second voltage of each time. In the descent amount measurement steps S2 and S3, the same amount of current (SOC) can be obtained. For example, when a current amount corresponding to 2% SOC is charged in the second voltage drop measuring step S2 for the first time, a current corresponding to 2% SOC in the second second voltage drop measuring step S2 is also charged. Each time the second voltage drop amount measurement step S2 is performed, such as charging the amount, the same current amount is charged or discharged, and the SOC is changed to the same side (+ side or-side) by a certain percentage. It can also be made.

  In each of the second voltage drop measurement steps S2 and S3, when the SOC of the secondary battery 1 is adjusted to the second SOC and the third SOC, charging or discharging is performed by a predetermined amount of current. As described above, the adjustment is performed by defining the amount of current. Therefore, the adjustment can be performed easily and with high accuracy compared to the case where the SOC adjustment is performed by defining a voltage having a large variation.

Next, from the first voltage drop amount ΔVA and the reference line, a first estimated SOC when the first voltage drop amount ΔVA in the secondary battery 1 to be inspected is measured is calculated. The estimation step S4 is performed.
Specifically, as shown in FIG. 5A, the first voltage drop amount ΔVA measured in the first voltage drop amount measurement step is applied to the reference line prepared in advance, The SOC value corresponding to the first voltage drop amount ΔVA on the reference line is calculated as the SOC when the first voltage drop amount ΔVA is measured, and is set as the first estimated SOC.

After the first estimated SOC is set, as shown in FIG. 5B, the first estimated SOC is charged or discharged in the adjustment step S21 in the first second voltage drop measurement step S2. The first secondary estimated SOC, which is the SOC when the second voltage drop amount ΔVB is measured, is calculated by adjusting the SOC by the amount of current that has been performed (S5).
Further, after calculating the first second-order estimated SOC, as shown in FIG. 5C, in the second second voltage drop measurement step S3 with respect to the first second-order estimated SOC. The second secondary estimated SOC, which is the SOC when the third voltage drop ΔVC is measured, is adjusted by adjusting the SOC by the amount of current that has been charged or discharged in the adjustment step S31 (S5). ). The second second estimated SOC is equal to the amount of current charged or discharged in the adjustment step S21 in the first second voltage drop measurement step S2 with respect to the first estimated SOC, and 2 It can also be calculated by adjusting the amount of current charged or discharged in the adjustment step S31 in the second voltage drop measurement step S3.

Thus, after setting the first estimated SOC, charging or discharging is performed in the adjustment steps S21 and S31 in the second voltage drop measurement steps S2 and S3 for the first estimated SOC. A plurality of second estimated SOCs (first second estimated SOC and second second estimated SOC corresponding to the plurality of second voltage drop measurement steps S2 and S3 are performed by adjusting the amount of current that has been performed. A second estimation step S5 for calculating the secondary estimation SOC) is performed.
In each second estimation step S5, since the SOC adjustment is performed by adding or subtracting the amount of current that has been charged or discharged, the value of each second estimated SOC with respect to the first estimated SOC is accurately determined. It is possible to calculate.

Next, the first estimated SOC, the first second estimated SOC, and the second second estimated SOC calculated as described above, and the measured first voltage drop amount ΔVA, second voltage drop Using the amount ΔVB and the third voltage drop amount ΔVC, an actual measurement line that is a graph showing the relationship between the estimated SOC and the voltage drop amount is created.
Specifically, as shown in FIG. 5D, point P1 (first estimated SOC, voltage drop ΔVA), point P2 (first second estimated SOC, voltage drop ΔVB), and point An actual measurement line creation step is performed in which a graph passing through P3 (second second-order estimated SOC, voltage drop amount ΔVC) is created as an actual measurement line (S61).

Then, the actual measurement line and the reference line are compared, and the presence or absence of a micro short circuit in the secondary battery 1 is determined according to the degree of coincidence between the actual measurement line and the reference line.
For example, the actual measurement line and the reference line are compared to determine whether or not the degree of coincidence between the actual measurement line and the reference line is greater than a preset threshold (S62). If the degree is less than or equal to the threshold value, it is determined that the secondary battery 1 has a micro short circuit (S63), and if the degree of coincidence between the measured line and the reference line is greater than the threshold value, it is determined that there is no micro short circuit (S64). .

Since the reference line indicates the relationship between the SOC and the voltage drop in a model secondary battery that is known not to have a micro short circuit, as shown in FIG. If the measured line is a non-defective secondary battery that does not have a micro short circuit, the degree of match between the measured line and the reference line is high (the deviation of the measured line from the reference line is small), and the secondary to be inspected. When the actual measurement line of the battery 1 is that of a micro short circuit secondary battery having a micro short circuit, the degree of coincidence between the actual measurement line and the reference line is low (the deviation of the actual measurement line from the reference line is large).
Therefore, as described above, it is possible to determine the presence or absence of a minute short circuit in the secondary battery 1 according to the degree of coincidence between the actual measurement line and the reference line.

  In addition, the measurement line creation process (S61), the process of determining whether or not the degree of coincidence between the measurement line and the reference line is greater than the threshold value (S62), and the process of determining that the secondary battery 1 has a micro short circuit ( The determination step S6 is configured by S63) and the step of determining that the secondary battery 1 does not have a micro short circuit (S64).

In the present embodiment, the second voltage drop amount measurement steps S2 and S3 are repeated twice to measure the second voltage drop amount ΔVB and the third voltage drop amount ΔVC.
This is the second SOC in the first second voltage drop measurement step S2 in addition to the measurement of the first voltage drop ΔVA in the first SOC in the first voltage drop measurement step S1. At least three different SOCs, such as measurement of the second voltage drop amount ΔVB and measurement of the third voltage drop amount ΔVC at the third SOC in the second second voltage drop amount measurement step S2. In this case, it is preferable to measure the voltage drop amount in order to appropriately create the actual measurement line, and the determination of the presence or absence of a micro short circuit in the secondary battery 1 can be performed with high accuracy.
However, the second voltage drop amount measurement step can be repeated three times or more, and the second battery drop amount measurement step is repeated three times or more, so that there is a minute short circuit in the secondary battery 1. This determination can be performed with higher accuracy.

As in this embodiment, the voltage drop amount is measured for a plurality of SOCs in one secondary battery 1, and the relationship between the measured voltage drop amount and the SOC is represented by an actual measurement line (line). Inspecting the presence or absence of a micro short circuit in the secondary battery 1 by comparing a reference line (line) that is a graph showing the relationship between the SOC and the voltage drop in a model secondary battery known to have no micro short circuit In other words, when the secondary battery 1 is adjusted to the first SOC at the start of inspection by comparing the measured voltage drop amount with a line instead of comparing with a point as in the prior art (S11). Even if the adjusted first SOC varies with respect to the target value, the presence or absence of a micro short circuit can be detected with high accuracy.
For this reason, the adjustment to the first SOC at the start of the inspection does not necessarily need to be strictly adjusted to the target SOC value, and can be performed roughly. Therefore, the SOC adjustment process is performed easily and in a short time. It is possible.

  In addition, since the voltage drop amount is measured for a plurality of SOCs in one secondary battery 1 to detect the presence or absence of a short-circuit in the secondary battery, internal resistance varies greatly between solids or lots. Even in the case of a secondary battery, it is possible to detect the presence or absence of a short circuit in the secondary battery with high accuracy without being affected by the variation.

Further, when the voltage drop amounts ΔVA, ΔVB, ΔVC in the present embodiment are measured in a range where the slope in the OCV curve is large (for example, the SOC is in the range of 0% to 10%), the voltage drop amount ΔVA · ΔVB once. The measurement time of ΔVC can be shortened (a large voltage drop amount ΔVA / ΔVB / ΔVC can be obtained with a short aging time), and the execution time of the inspection process of the secondary battery 1 can be shortened. .
In this case, at least one of the SOCs for measuring the voltage drop amounts ΔVA, ΔVB, ΔVC in the first voltage drop amount measurement step S1 and the second voltage drop amount measurement step S2 is 0% to 10%. By setting the value within the range, the execution time of the inspection process of the secondary battery 1 can be shortened.

  Furthermore, the voltage drop amounts ΔVA, ΔVB, and ΔVC are measured with SOCs having different slopes in the OCV curve, so that the measured line and the reference line of the non-defective secondary battery and the micro short-circuited secondary battery are measured. Since a difference in the degree of coincidence appears greatly, the presence / absence of a micro short circuit can be detected with high accuracy.

[Example]
Next, the Example of the inspection method of the secondary battery 1 is demonstrated.
In this embodiment, 21 non-defective samples of the secondary battery 1 having no micro short circuit are created, and 4 micro short samples of the secondary battery 1 having a micro short circuit are created. The presence or absence of a micro short circuit was detected by the inspection method for the secondary battery 1 according to the invention.

As a non-defective sample of the secondary battery 1, 90 wt% of LiNiCoMnO ₂ as a positive electrode active material, 5 wt% of acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder as a positive electrode plate. A positive electrode mixture paste containing 5 wt% was applied to a 15 μm thick aluminum foil as a current collector.
Moreover, as a negative electrode plate, 98 wt% of a natural graphite-based active material as a negative electrode active material, 1 wt% of carboxymethylcellulose (CMC) as a thickener, and 1 wt% of a styrene-butadiene copolymer (SBR) as a binder. % Negative electrode mixture paste was applied to a 10 μm thick copper foil as a current collector.

In addition, a separator having a thickness of 20 μm made of a single layer structure of polypropylene (PP), a single layer structure of polyethylene (PE), or a two-layer structure of polypropylene (PP) and polyethylene (PE) is used. It was.
Further, as an electrolytic solution, LiPF ₆ was added to a solvent in which EC (ethylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) were mixed at a ratio of 3: 3: 4 (weight ratio). Those dissolved at a concentration of 0 M were used.
Moreover, it comprised in the secondary battery with a capacity | capacitance of 22.5 Ah.

As for the micro short-circuit sample of the secondary battery 1, an iron foreign material having a size of 70 μm and an iron foreign material having a size of 180 μm are charged on the positive electrode side of the secondary battery having the same specifications as the above-mentioned non-defective sample. What was done was used.
Two fine short-circuit samples into which 70 μm foreign matter was introduced and two short-circuit samples into which 180 μm foreign matter was introduced were prepared.

  No. 21 for 21 non-defective samples. Sample Nos. 1-21 No. is applied to a micro short-circuit sample to which a foreign substance of 70 μm is added. Sample Nos. 22 and 23 No. is applied to a micro short-circuited sample with 180 μm of foreign matter added. Sample Nos. 24 and 25 Was attached.

  For each of the above-mentioned non-defective samples and micro short-circuit samples (samples Nos. 1 to 25), initial charging was performed at 1C from 0 V to 4.1 V at 25 ° C., and at 4.1 V and 60 ° C. Each non-defective sample and minute short-circuit sample were initially activated by being left for 1 day (aging), and then the presence or absence of a minute short-circuit was detected by the inspection method for the secondary battery 1.

Detection of the presence or absence of a short-circuit by the inspection method of the secondary battery 1 was performed according to the following flow.
First, sample no. Samples 1 to 25 were adjusted to the first SOC and allowed to stand in an environment of 20 ° C. for 5 hours in order to stabilize the temperature and voltage.
Although the target value for adjusting each sample to the first SOC is 4%, it is not strictly adjusted to 4% SOC, but the first SOC is a value within a range of several percent centered on 4%. The first SOC adjustment was completed when it was able to be adjusted.

  Next, each sample is left to stand for 20 hours in an environment of 20 ° C. to perform an aging treatment, measure the voltage V1 before the aging treatment and the voltage V2 after the aging treatment, and subtract the voltage V2 from the voltage V1. Thus, the first voltage drop amount ΔVA was calculated (first voltage drop amount measurement step).

Thereafter, each sample is charged by a constant current amount (1% charge is charged for 2% SOC), and each sample is adjusted to the second SOC. In this case, the second SOC is a value different from the first SOC.
Each sample adjusted to the second SOC is left to stand in an environment of 20 ° C. for 20 hours to perform an aging treatment, and a voltage V3 before the aging treatment and a voltage V4 after the aging treatment are measured, respectively. By subtracting V4, the second voltage drop amount ΔVB was calculated (first second voltage drop amount measurement step).

Further, each sample is charged by the amount of the constant current (1C charge is charged for 2% SOC), and each sample is adjusted to the third SOC. In this case, the third SOC has a different value from the first SOC and the second SOC.
Each sample adjusted to the third SOC is left to stand for 20 hours in an environment of 20 ° C. to perform an aging treatment, and measure a voltage V5 before the aging treatment and a voltage V6 after the aging treatment, respectively. By subtracting V6, the third voltage drop amount ΔVC was calculated (second second voltage drop amount measurement step).

Further, each sample is charged by the amount of the constant current (charging for 2% SOC by 1C charging), and each sample is adjusted to the fourth SOC. In this case, the fourth SOC is different from the first SOC, the second SOC, and the third SOC.
Each sample adjusted to the fourth SOC is left to stand in an environment of 20 ° C. for 20 hours to perform an aging treatment, and measure the voltage V7 before the aging treatment and the voltage V8 after the aging treatment, respectively. By subtracting V8, the fourth voltage drop amount ΔVD was calculated (second second voltage drop amount measurement step).
Thus, in the present example, the second voltage drop amount measurement step was repeated three times.

Next, as shown in FIG. 6, the first voltage drop amount ΔVA is applied to a reference line prepared in advance, and the SOC value corresponding to the first voltage drop amount ΔVA is set on the reference line. The first estimated SOC was set.
Further, the first secondary estimated SOC is calculated by adding the charge amount for 2% SOC to the first estimated SOC, and the charge amount for 2% SOC is added to the first second estimated SOC. Then, the second second estimated SOC was calculated, and the third second estimated SOC was calculated by adding the charge amount for 2% SOC to the second second estimated SOC.

Next, the first estimated SOC, the first second estimated SOC, the second second estimated SOC, the third second estimated SOC calculated as described above, and the measured first voltage drop. Using the amount ΔVA, the second voltage drop amount ΔVB, the third voltage drop amount ΔVC, and the fourth voltage drop amount ΔVD, an actual measurement line that is a graph showing the relationship between the estimated SOC and the voltage drop amount was created. .
That is, point P1 (first estimated SOC, voltage drop ΔVA), point P2 (first second estimated SOC, voltage drop ΔVB), point P3 (second second estimated SOC, voltage drop) ΔVC) and a graph passing through point P4 (third second-order estimated SOC, voltage drop amount ΔVC) were created as actual measurement lines.

And the said measurement line and the reference line were compared, and the presence or absence of the micro short circuit in the secondary battery 1 was determined according to the coincidence degree of the measurement line and the reference line.
Comparison between the actual measurement line and the reference line was performed as follows.

First, in the reference line, a voltage drop amount (first value) corresponding to each second-order estimated SOC (first second-order estimated SOC, second second-order estimated SOC, third second-order estimated SOC). The reference voltage drop amount ΔVB ′, the second reference voltage drop amount ΔVC ′, and the third reference voltage drop amount ΔVD ′) were calculated.
Next, the absolute value of the difference between the voltage drop amount ΔVB and the first reference voltage drop amount ΔVB ′ (= the absolute value of ΔVB−ΔVB ′) d1, the voltage drop amount ΔVC, and the second reference voltage drop amount ΔVC ′. The absolute value of the difference (= the absolute value of ΔVC−ΔVC ′) d2 and the absolute value of the difference (the absolute value of ΔVD−ΔVD ′) d3 from the voltage drop amount ΔVD and the third reference voltage drop amount ΔVD ′ are obtained. The average value dave of the values d1, d2, and d3 was calculated.

If the average value calculated in this way is small, the degree of divergence between the actual measurement line and the reference line is small, and the degree of coincidence between the actual measurement line and the reference line is high. If the average value dave is large, the actual measurement line and the reference line are high. It can be said that the degree of deviation from the line is large and the degree of coincidence between the measured line and the reference line is low.
Therefore, the calculated average value dave is used as a value indicating the degree of coincidence between the measured line and the reference line, and the average value dave is compared with a preset threshold value. For example, it is determined that each sample does not have a micro short circuit (each sample is a non-defective sample), and if the average value “dave” is larger than the threshold value, each sample has a micro short circuit (each sample is a micro short sample). did.

Regarding the threshold value to be compared with the average value “dave”, No. The median value M of the average value dave and the standard deviation σ of the average value dave in each of the samples 1 to 21 were determined, and “M + 3σ” was used as the threshold value.
That is, if the average value “dave” of each sample (samples No. 1 to 25) is equal to or less than “M + 3σ”, it is determined that there is no micro short circuit in each sample (each sample is a non-defective sample), and “M + 3σ” If it is larger than that, it is determined that each sample has a micro short circuit (each sample is a micro short circuit sample).

Next, the detection result of the presence or absence of the micro short circuit by the inspection method of the secondary battery 1 will be described.
FIG. 7 shows the voltage drop amount difference average value (dave) between the reference line and the actual measurement line for each good product sample and minute short circuit sample.
The horizontal axis of the graph in FIG. No. of each sample No. Nos. 1 to 21 show non-defective samples. Reference numerals 22 to 25 denote micro short-circuit samples. In addition, the vertical axis of the graph in FIG. 7 indicates the voltage drop amount difference average value (dave) between the reference line and the actual measurement line.

According to FIG. 7, about the good sample (No. 1-21), the value of the average value dave in all the samples is below a threshold value (M + 3σ), and all the good sample (No. 1-21) Can be determined to be a non-defective secondary battery 1 without a micro short circuit.
Moreover, about the micro short circuit sample (No. 22-25), the value of the average value dave in all the samples is larger than a threshold value (M + 3σ), and all the micro short circuit samples (No. 22-25) are used. It can be determined that the secondary battery 1 has a minute short circuit.
Thus, according to the present inspection method, it is possible to detect the presence or absence of a micro short circuit in the secondary battery 1 with high accuracy.

  In addition, as shown in FIG. 8, when the voltage drop amount during one aging process is measured and the measured value is compared with the reference voltage drop amount to detect the presence or absence of a micro short circuit as in the conventional case. It took about 30 days to measure the amount of voltage drop due to the aging process (self-discharge) (if the aging process is not performed for about 30 days or more, there is a voltage drop enough to determine the presence or absence of a micro short circuit. However, in this secondary battery inspection method, each aging treatment (self-discharge) can be about 3 days (in each aging treatment, the voltage drop in the aging treatment for about 3 days). Therefore, the inspection time can be greatly shortened.

DESCRIPTION OF SYMBOLS 1 Secondary battery 2 Battery case 3 Electrode body 31 Positive electrode 32 Negative electrode 33 Separator ΔVA First voltage drop amount ΔVB Second voltage drop amount ΔVC Third voltage drop amount

Claims (3)

A method for inspecting a secondary battery comprising an electrode body formed by laminating a positive electrode, a negative electrode, and a separator so that the separator is interposed between the positive electrode and the negative electrode,
A first voltage drop measuring step of adjusting the secondary battery to an arbitrary SOC, performing an aging process, and measuring a voltage drop of the secondary battery during the aging process;
It is a step repeatedly performed a plurality of times after the first voltage drop amount measuring step, wherein the secondary battery is charged or discharged by an arbitrary amount of current, and the secondary battery is A second voltage drop measurement step for adjusting the SOC to be different from all the SOCs when measuring the voltage drop and then performing an aging process to measure the voltage drop of the secondary battery during the aging process. When,
A reference indicating the relationship between the voltage drop amount measured in the first voltage drop amount measurement step and the SOC and the voltage drop amount in the model secondary battery in which it is known that there is no micro short circuit calculated in advance. A first estimation step of calculating, from the line, an SOC when the voltage drop amount is measured in the first voltage drop amount measurement step in the secondary battery as a first estimated SOC;
The first estimated SOC is adjusted for the amount of current charged or discharged in the plurality of second voltage drop measurement steps, and the second voltage drop measurement is performed a plurality of times. A second estimating step for calculating a plurality of second-order estimated SOCs corresponding to the steps;
The voltage drop amount measured in the first voltage drop amount measurement step and the plurality of second voltage drop amount measurement steps, a first estimated SOC and a plurality of second estimated SOCs corresponding to the voltage drop amounts. Comparing the actual measurement line indicating the relationship with the reference line, and determining whether there is a micro short-circuit in the secondary battery according to the degree of coincidence between the actual measurement line and the reference line,
A method for inspecting a secondary battery. In the determination step, the determination of the presence or absence of a micro short circuit in the secondary battery according to the degree of match between the actual measurement line and the reference line is
Calculating a voltage drop amount corresponding to each of the second-order estimated SOCs in the reference line;
Comparing an average value of a difference between a voltage drop amount corresponding to each second estimated SOC in the actual measurement line and a voltage drop amount corresponding to each second estimated SOC in the reference line with a preset threshold value. By
The method for inspecting a secondary battery according to claim 1. Each SOC at the time of measuring the voltage drop amount in the first voltage drop amount measurement step and the plurality of second voltage drop amount measurement steps is set to a value in which the slope of the OCV curve of the secondary battery is different from each other. ,
In addition, at least one of the SOCs when the voltage drop amount is measured in the first voltage drop measurement step and the plurality of second voltage drop measurement steps is within a range of 0 to 10%. Set to the value of
The method for inspecting a secondary battery according to claim 1 or 2, characterized in that:

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