JP2017037764A - Method for inspecting nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve inspection accuracy in a method for inspecting a nonaqueous electrolyte secondary battery.SOLUTION: An inspection method proposed in the present invention includes: an assembly step A, an initial charging step B, a high-temperature aging step C, a self discharge step D, and a quality determining step E. During the quality determining step E, a voltage drop amount ΔVdx in the self discharging step D is corrected, and quality is determined on the basis of a voltage drop amount ΔVdy after having been corrected.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a method for inspecting a nonaqueous electrolyte secondary battery.

  Japanese Patent Laying-Open No. 2015-90806 discloses an invention relating to a method for inspecting a nonaqueous electrolyte secondary battery. In such a non-aqueous electrolyte secondary battery inspection method, the battery is assembled, subjected to initial charging to a predetermined voltage, subjected to high temperature aging that is maintained for a certain period of time in a high temperature range, and then left at a normal temperature range for a certain period of time. To self-discharge. And when the short circuit of a positive electrode and a negative electrode has arisen in the electrode body of a battery in the high temperature aging process etc., the amount of voltage drops will increase in a self-discharge process. Focusing on this, a threshold is set for the voltage drop amount in the self-discharge process, and “with internal short circuit” and “without internal short circuit” are determined (paragraph 0017, etc.).

  Patent Document 1 discloses a low voltage leaving step in which the battery assembly after the self-discharge step is further discharged to a low voltage region of 3.45 V or less and then left in the low voltage region for 1 to 3 hours. Has been. Gas is generated when the battery assembly is initially charged and subjected to high temperature aging. If charging / discharging is performed as it is, charging unevenness occurs in the gas biting portion of the electrode body, which causes deterioration of battery characteristics. In the low voltage leaving step, the battery assembly after the self-discharge step is left in a low voltage region of 3.45V or less. As a result, even when gas is generated in the initial charging or high-temperature aging treatment, the electrolytic solution impregnates the gas biting portion of the electrode body. In patent document 1, it is supposed that the phenomenon that battery performance (for example, battery capacity) falls by charging unevenness in subsequent charging / discharging processing due to such unevenness can be suppressed.

Japanese Patent Laying-Open No. 2015-90806

  By the way, according to the knowledge of the present inventors, when the time of the high temperature aging process is shortened in a series of inspection processes based on the voltage drop amount in the self-discharge process, the voltage after the high temperature aging process tends to vary. This variation affects the variation in the amount of voltage drop in the self-discharge process, and in the inspection based on the amount of voltage drop in the self-discharge process, even if it should be determined that there is “internal short circuit”, “no internal short circuit”. An event that can be determined can occur.

  In addition, even if it is determined that there is no internal short circuit if the voltage drop amount is smaller than the threshold when it should be determined that there is an internal short circuit in this process, voltage adjustment, resistance measurement, and stack status before shipment It can be checked that there is an “internal short circuit” in other post-processes such as self-discharge at. For this reason, it is possible to prevent the battery that should be determined as “with internal short circuit” in the inspection of the self-discharge process from being finally shipped. However, if the accuracy of the inspection in the self-discharge process is improved, the processing burden of the subsequent process is reduced, and the cost can be reduced. For this reason, this inventor wants to improve the precision of the quality determination of a battery based on the amount of voltage drops in a self-discharge process.

The inspection method proposed here includes the following steps A to E.
Step A: Assembling a battery assembly in which an electrode body and a nonaqueous electrolyte are accommodated in a battery case (assembly step A);
Step B: a step of charging the battery assembly to a predetermined voltage value (initial charging step B);
Step C: a step of holding the battery assembly charged in the initial charging step B in a predetermined high temperature range for a predetermined time (high temperature aging step C);
Step D: Step of leaving the battery assembly for a predetermined time after the high temperature aging step C (self-discharge step D);
Step E: A step in which the voltage drop amount ΔVdx in the self-discharge step D is corrected and a pass / fail judgment is made based on the corrected voltage drop amount ΔVdy (pass / fail judgment step E) (see FIG. 4).
According to this inspection method, in the corrected voltage drop amount ΔVdy, the variation in the voltage drop amount ΔVd in the self-discharge process D is reduced, and the accuracy of the quality determination can be improved.

FIG. 1 is a graph schematically showing an example of each step of the non-aqueous electrolyte secondary battery before shipment and a voltage change of the non-aqueous electrolyte secondary battery. FIG. 2 is a graph showing a typical relationship between the time of the high temperature aging process C and the start voltage D1 (V) of the self-discharge process D. FIG. 3 is a graph schematically showing a tendency that the start voltage D1 of the self-discharge process D varies. FIG. 4 is a graph showing the relationship between the start voltage D1 (V) of the self-discharge process D and the self-discharge amount (mV / 3 days). FIG. 5 is a graph showing the difference (▲) in the voltage drop amount ΔVdx before correction and the difference (●) in the voltage drop amount ΔVdy after correction. FIG. 6 is a flowchart showing an example of a work procedure from the process A to the self-discharge process D. FIG. 7 is a graph showing the elapsed time and voltage drop amount ΔVd of the self-discharge process D for each lot.

  Hereinafter, an embodiment of a method for inspecting a nonaqueous electrolyte secondary battery proposed here will be described.

The proposed method for inspecting a nonaqueous electrolyte secondary battery includes an assembly process A, an initial charging process B, a high-temperature aging process C, a self-discharge process D, and a pass / fail judgment process E.
The assembly process A is a process of assembling a battery assembly in which an electrode body and a nonaqueous electrolyte are accommodated in a battery case.
The initial charging step B is a step of charging the battery assembly assembled in the step A to a predetermined voltage value.
The high temperature aging process C is a process of holding the battery assembly charged in the initial charging process B in a predetermined high temperature range for a predetermined time.
The self-discharge process D is a process in which the self-discharge process D is left for a predetermined time after the high-temperature aging process C.
The pass / fail judgment step E is a step in which the voltage drop amount ΔVdx in the self-discharge step D is corrected, and pass / fail judgment is performed based on the corrected voltage drop amount ΔVdy (see FIG. 4).
According to this inspection method, in the corrected voltage drop amount ΔVdy, the variation in the voltage drop amount ΔVd in the self-discharge process D is reduced, and the accuracy of the quality determination can be improved.

  In the non-aqueous electrolyte secondary battery that is the subject of this inspection method, the battery case, electrode body, non-aqueous electrolyte, and the like are not particularly limited. Battery cases, electrode bodies, non-aqueous electrolytes, and the like are known as battery structures, and examples include those disclosed in Patent Document 1 described above. For this reason, in this specification, detailed explanation about this is omitted. In addition, for the steps A to D, necessary basic procedures and the like are disclosed in, for example, Patent Document 1 described above, and in the present specification, description overlapping therewith is omitted.

  FIG. 1 is a graph schematically showing an example of each step of the non-aqueous electrolyte secondary battery before shipment and a voltage change of the non-aqueous electrolyte secondary battery. In FIG. 1, the horizontal axis indicates the passage of time, and the vertical axis indicates the voltage. In the pre-shipment process of the nonaqueous electrolyte secondary battery, the self-discharge process D is performed from the initial charging process B as shown in FIG. Thereafter, capacity measurement and resistance measurement are performed while discharging (F), charging is performed in stages (G, H), adjusted to an appropriate voltage, and then shipped. FIG. 1 only shows an example of the process before shipment of the nonaqueous electrolyte secondary battery, and the proposed method for inspecting the nonaqueous electrolyte secondary battery is shown in this example unless otherwise specified. It is not limited.

  In FIG. 1, the voltage indicates the change in the open circuit voltage of the battery (also referred to herein as “battery assembly”). As shown in FIG. 1, in the initial charging step B, the voltage increases due to charging and is charged to a predetermined voltage. In the high temperature aging process C and the self-discharge process D, the voltage gradually decreases during aging. Here, the start voltage D1 of the self-discharge process D (in other words, the voltage after the high temperature aging process C) may vary depending on the high temperature aging process C.

  FIG. 2 is a graph showing a typical relationship between the time of the high temperature aging process C and the start voltage D1 (V) of the self-discharge process D. In FIG. 2, the relationship between the time of the high temperature aging process C and the start voltage D1 (see FIG. 1) of the self-discharge process D is shown for a plurality of samples. In this embodiment, the self-discharge process D is transferred as it is after the high-temperature aging process C. For this reason, the start voltage D1 of the self-discharge process D is a voltage after the high temperature aging process C. As shown in FIG. 2, when the time of the high temperature aging process C is sufficiently long, the variation of the voltage after the high temperature aging process C (the start voltage of the self-discharge process due to the course) is reduced. For example, as shown in S1, when the high temperature aging process C is lengthened to about 120 hours (5 days), the voltage after the high temperature aging process C tends to be almost stable. However, when the time of the high-temperature aging process C is short, the start voltage D1 of the self-discharge process D tends to vary as described above. For example, as shown in S2, if the high temperature aging process C is about 20 hours, the degree of voltage drop in the high temperature aging process C varies. Although the high temperature aging process C may be lengthened to about 120 hours (5 days), the production process becomes longer and the cost increases as the high temperature aging process C becomes longer. Considering productivity, it is desirable to shorten the time of the high temperature aging process C.

  In addition, as a method for accurately inspecting the presence / absence of “internal short circuit” in the self-discharge process D, for example, after the high-temperature aging process C, the self-discharge process D may be charged to a predetermined voltage. In this case, since the voltage is adjusted before the self-discharge process D, when a short circuit occurs in the battery assembly in the high-temperature aging process C, the amount of voltage drop in the self-discharge process D increases. For this reason, in the self-discharge process D, “presence / absence of internal short circuit” can be determined with higher accuracy. However, since a process of charging after the high temperature aging process C and before the self-discharge process D is added, the number of inspection processes increases and the cost increases. For this reason, this inventor thinks that it is desirable to transfer to the self-discharge process D, without charging before the self-discharge process D after the high temperature aging process C.

  FIG. 3 is a graph schematically showing a tendency that the start voltage D1 of the self-discharge process D varies. In FIG. 3, L <b> 1 indicates a typical sample voltage change from the initial charging process B to the self-discharge process D. The voltage drop ΔVd in the self-discharge process D is the difference (D2−D1) between the start voltage D1 of the self-discharge process D and the end-time voltage D2 of the self-discharge process D. In FIG. 3, the change in voltage in the high temperature aging process C is exaggerated, and the scales of time (horizontal axis) and voltage (vertical axis) do not match those in FIG. In this specification, voltage drop amount ΔVd = end-time voltage D2−starting voltage D1 (D1> D2). Therefore, in FIG. 4 and FIG. 7, the voltage drop amount ΔVd is represented by minus (−).

  L2 shows an example of a voltage change of a sample in which the voltage is greatly lowered in the high temperature aging process C and the start voltage D1x of the self-discharge process D is low. As shown in FIG. 3, when the voltage is greatly reduced in the high temperature aging process C, the start voltage D1x of the self-discharge process D is low. As a tendency found by the present inventor, the lower the starting voltage D1 of the self-discharge process D, the smaller the voltage drop amount ΔVdx in the self-discharge process D. The voltage drop ΔVdx in the self-discharge process D is a difference (D2x−D1x) between the start voltage D1x of the self-discharge process D and the end-time voltage D2x of the self-discharge process D.

  From the tendency shown in FIG. 2 and FIG. 3, the present inventor has found the following findings. When the time of the high temperature aging process C is short, the voltage after the high temperature aging process C (starting voltage D1 of the self-discharge process D) tends to vary (FIG. 2). The lower the starting voltage D1 of the self-discharge process D, the smaller the voltage drop amount ΔVd in the self-discharge process D (FIG. 3).

  The lower the start voltage D1 of the self-discharge process D, the smaller the voltage drop ΔVd in the self-discharge process D is because the present inventor found that the lower the start voltage D1 of the self-discharge process D, the lower the battery in the self-discharge process D. It is presumed that the activity of is small. In the pass / fail determination for determining the presence or absence of an internal short circuit of the battery based on the start voltage D1 of the self-discharge process D, a threshold is set for the voltage drop amount ΔVd in the self-discharge process D. For this reason, if the voltage drop amount ΔVd in the self-discharge process D is small, it may be determined that “no internal short circuit” (no abnormality). However, when the voltage drop of the high temperature aging process C is large and the start voltage D1 of the self discharge process D is low, such as an internal short circuit occurring in the high temperature aging process C, the voltage drop amount ΔVd in the self discharge process D is small. Become. For this reason, this inventor estimates that it may be determined that "there is no internal short circuit" (no abnormality). Thus, according to the knowledge obtained by the present inventors, when the time of the high-temperature aging process C is shortened, the variation in the start voltage D1 of the self-discharge process D increases. This variation affects the variation in the voltage drop amount ΔVd in the self-discharge process D. For this reason, in the process of determining the quality of the battery assembly based on the voltage drop amount ΔVd in the self-discharge process D, the accuracy of the quality determination is lowered.

  Next, FIG. 4 is a graph showing the relationship between the start voltage D1 (V) of the self-discharge process D and the self-discharge amount (mV / 3 days). FIG. 4 shows the relationship between the start voltage D1 (V) of the self-discharge process D and the voltage drop (mV / 3 days) when the high-temperature aging process C is about 20 hours. As shown in FIG. 4, the present inventor shows that the higher the start voltage D1 of the self-discharge process D, the higher the voltage drop amount ΔVd in the self-discharge process D (see FIG. 3), and the start voltage of the self-discharge process D. It was found that there is a correlation Df between D1 and the voltage drop amount ΔVd. In the example shown in FIG. 4, the correlation Df is a linear approximation. The correlation Df can typically be linearly approximated, but is not necessarily limited to linear approximation.

  The inventor wants to improve the accuracy of the battery assembly quality determination based on the start voltage D1 of the self-discharge process D. In the non-aqueous electrolyte secondary battery inspection method proposed here, the voltage drop amount ΔVd in the self-discharge process D is corrected in the process E for determining pass / fail. The quality of the battery is determined based on the corrected voltage drop amount. In this case, the variation in the amount of voltage drop after correction is reduced. For this reason, it is expected that the accuracy of the battery assembly quality determination is improved by setting an appropriate threshold for the corrected voltage drop amount.

  Here, the correction of the voltage drop amount ΔVd in the self-discharge process D will be described. For example, as shown in FIG. 4, the voltage drop amount ΔVd may be corrected based on the correlation Df between the start voltage D1 of the self-discharge process D and the voltage drop amount ΔVd. In FIG. 4, a voltage drop amount (hereinafter referred to as a reference voltage drop amount ΔVdA) when the start voltage D1 of the self-discharge process D is 3.90 V is used as a reference. As shown in FIG. 4, it is assumed that the start voltage D1 of the self-discharge process D of a certain battery is D1i. In this case, based on the correlation Df, the “predicted voltage drop amount ΔVdi” that can be measured when the start voltage D1 of the self-discharge process D is “D1i” is calculated. Then, a difference (ΔVdi−ΔVdA) between the reference voltage drop amount ΔVdA and the predicted voltage drop amount ΔVdi is calculated. This difference (ΔVdi−ΔVdA) is set as a correction value z = (ΔVdi−ΔVdA) for the actually measured voltage drop amount ΔVd.

  In this case, the corrected voltage drop ΔVdy is calculated as ΔVdx−z with respect to the voltage drop ΔVdx (voltage drop before correction) in the self-discharge process D actually measured in a certain sample. By this correction, the corrected voltage drop amount ΔVdy becomes a value that can be compared with the voltage drop amount ΔVdA when the start voltage D1 of the self-discharge process D is 3.90V. In other words, in this case, the corrected voltage drop amount ΔVdy is a converted value when the start voltage D1 of the self-discharge process D is 3.90V. In the pass / fail judgment step E, the pass / fail judgment of the battery may be performed based on the corrected battery voltage drop ΔVdy. For example, by setting an appropriate threshold value for the corrected battery voltage drop ΔVdy, the battery quality can be determined more accurately.

  FIG. 5 is a graph showing the difference (▲) in the voltage drop amount ΔVdx before correction and the difference (●) in the voltage drop amount ΔVdy after correction. In FIG. 5, the horizontal axis represents the lot number. The vertical axis represents the difference in voltage drop ΔVd. In the example of FIG. 5, production management is performed with 30 batteries as one lot. The abscissa indicates the lot number. The difference in the voltage drop amount ΔVd on the vertical axis is the difference between the maximum value of the voltage drop amount ΔVd and the minimum value of the voltage drop amount ΔVd in each lot. In FIG. 5, the difference in the voltage drop amount ΔVdx before correction in each lot is shown by a plot of “▲”. The difference in the voltage drop amount ΔVdy after correction is shown by a plot “●”. The number of batteries in each lot is not limited to 30. In this case, for example, in FIG. 4, the correlation Df may be calculated between the start voltage D1 of the self-discharge process D and the voltage drop amount ΔVd for each lot. And it is good to correct | amend voltage drop amount (DELTA) Vd in the self-discharge process D for every lot.

  As a result, as shown in FIG. 5, the difference (の) in the voltage drop amount ΔVdy after correction is smaller than the difference (の) in the voltage drop amount ΔVdx before correction. That is, by correcting the voltage drop amount ΔVd in the self-discharge process D measured for each battery for each lot, the variation in the corrected voltage drop amount ΔVdy is reduced. That is, the corrected voltage drop amount ΔVdy corrects the variation in the voltage drop amount ΔVd of each battery due to the variation in the start voltage D1 of the self-discharge process D to be small. In this case, by setting an appropriate threshold value for the corrected voltage drop ΔVdy of the battery for each lot and determining the quality, the quality of the battery can be determined more accurately.

  Thus, as a knowledge of the present inventor, when the pass / fail determination is made based on the voltage drop amount ΔVd in the self-discharge process D, it is preferable to make it for each lot. That is, according to the knowledge of the present inventors, the voltage drop amount ΔVd in the self-discharge process D varies from lot to lot. Further, the longer the time of the self-discharge process D, the larger the variation in the voltage drop amount ΔVd for each lot. Therefore, for each lot, it is preferable to correct the voltage drop amount ΔVd in the battery self-discharge process D and perform the pass / fail determination based on the corrected voltage drop amount ΔVdy.

  FIG. 6 is a flowchart showing an example of a work procedure from the process A to the self-discharge process D. “K” in FIG. 6 indicates a place where flows are combined. As shown in FIG. 6, in the process A for assembling a battery assembly in which an electrode body and a non-aqueous electrolyte are accommodated in a battery case, sealed can welding A1, cell drying A2, liquid injection A3, liquid inlet welding A4 , The permeation standby A5 and the cell restraint A6 are included. Here, in the sealed can welding A1, the battery case is closed except for the liquid injection port. For example, an electrode body is accommodated in a battery case, and a lid having a liquid injection port is attached to and welded to the battery case in which the electrode body is accommodated. In cell drying A2, the battery assembly with the lid welded is placed in a dry atmosphere to evaporate moisture in the battery case. In the injection liquid A3, the nonaqueous electrolyte is accommodated in the battery case. For example, a non-aqueous electrolyte (here, liquid) may be injected into the battery case from the liquid inlet of the lid. In the liquid inlet welding A4, the liquid inlet is closed. In the permeation standby A5, the battery assembled as described above is left until the injected nonaqueous electrolyte (electrolytic solution) is sufficiently impregnated in the electrode body. In cell restraint A6, the battery is restrained.

  FIG. 7 is a graph showing the elapsed time and voltage drop amount ΔVd of the self-discharge process D for each lot. The horizontal axis of FIG. 7 indicates the elapsed time of the self-discharge process D, and the vertical axis indicates the voltage drop amount ΔVd. In FIG. 7, the average value for each lot is shown for the voltage drop amount ΔVd in the self-discharge process D. Here, as for the voltage drop amount ΔVd in the self-discharge process D, the open circuit voltage may be measured for each battery in each lot, for example, every 30 minutes. Thereby, as shown in FIG. 7, the time lapse of the voltage drop amount ΔVd in the self-discharge process D can be grasped as an average value for each lot. The voltage drop amount ΔVd in the self-discharge process D varies from lot to lot. Further, as the elapsed time of the self-discharge process D becomes longer as shown in FIG. 7, the variation in the voltage drop amount ΔVd in the self-discharge process D for each lot becomes larger.

  According to the knowledge of the present inventor, as shown in FIG. 7, the voltage drop amount ΔVd in the self-discharge process D is slightly different for each lot in production management. For example, conditions such as the drying time in the cell drying A2 and the temperature and humidity in the drying atmosphere cause a difference for each lot. Due to the difference in conditions in the cell drying A2, for example, a difference occurs in the amount of moisture remaining in the battery case. This difference in water content affects the gas generation in the initial charging step B. The gas generated in the initial charging process B causes a difference in the self-discharge amount in the high-temperature aging process C, affects the start voltage D1 of the self-discharge process D, and also affects the voltage drop amount ΔVd in the self-discharge process D. Thus, the influence by cell drying A2 is large.

  For this reason, as described above, when the quality determination is performed based on the voltage drop amount ΔVd in the self-discharge process D, it is preferable to perform the quality determination for each lot. In this case, for example, when the correlation Df (see FIG. 4) is obtained between the start voltage D1 of the self-discharge process D and the voltage drop ΔVd for each lot, and the voltage drop ΔVd in the self-discharge process D is corrected. Good. In particular, the quality determination may be performed for each lot (dry lot) in the cell drying process. That is, the quality determination based on the voltage drop amount ΔVd in the self-discharge process D may be performed for each battery group in which the cell drying process is performed in the same process. In this case, for example, a correlation Df (see FIG. 4) is obtained between the start voltage D1 of the self-discharge process D and the voltage drop ΔVd for each dry lot, and the voltage drop ΔVd in the self-discharge process D is corrected. Good. This further improves the accuracy of the pass / fail judgment.

  The non-aqueous electrolyte secondary battery inspection method proposed here has been described above. However, the non-aqueous electrolyte secondary battery inspection method proposed here is not limited to the above-described embodiment unless otherwise specified. .

A Assembly process B Initial charging process C High-temperature aging process D Self-discharge process D1 Start voltage D2 End voltage Df Correlation E Pass / fail judgment process ΔVd Voltage drop amount ΔVdx in self-discharge process D Voltage drop amount ΔVdy before correction Voltage after correction Descent amount

Claims (2)

Assembling a battery assembly in which an electrode body and a non-aqueous electrolyte are housed in a battery case;
An initial charging step of charging the battery assembly to a predetermined voltage value;
A high temperature aging step for holding the battery assembly charged in the initial charging step in a predetermined high temperature region for a predetermined time; and
A self-discharge step that is allowed to stand for a predetermined time after the high-temperature aging step;
A method for inspecting a non-aqueous electrolyte secondary battery, comprising: correcting a voltage drop amount in the self-discharge step, and performing a pass / fail determination based on the corrected voltage drop amount. Assembling the battery assembly includes
Accommodating the electrode body in the battery case;
A cell drying step of drying the battery case containing the electrode body;
After the drying step, containing the non-aqueous electrolyte in a battery case,
The non-aqueous electrolyte secondary battery inspection method according to claim 1, wherein the quality determination is performed for each lot in the cell drying step.

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