JP2020194631A - Inspection method - Google Patents

Abstract

To provide an inspection method capable of determining presence or absence of minute short circuit in a power storage module, in a short time with high accuracy.SOLUTION: An inspection method includes a second charging step S4 of charging an initially charged power storage module, at a rate lower than that in a first charging step, until SOC becomes more than 0% and 20% or less, a first shelf step S5 of leaving the power storage module, charged in the second charging step, for a first prescribed time, a first measurement step S6 of measuring the voltage of the power storage module left in the first shelf step, a second shelf step S7 of leaving the power storage module, measured in the first measurement step, for a second prescribed time, a second measurement step S8 of measuring the voltage of the power storage module left in the second shelf step, and a determination step S9 of determining presence or absence of minute short circuit, on the basis of difference of the voltage measured in the first measurement step and the voltage measured in the second measurement step.SELECTED DRAWING: Figure 3

Description

The present invention relates to an inspection method for a power storage module.

The manufacturing process of the power storage module includes a conditioning process and an aging process. The conditioning step is a step of activating the power storage module as a battery by repeatedly charging and discharging the power storage module for a plurality of cycles. The aging step is a step of discharging the power storage module initially charged in the conditioning step to a predetermined voltage and then leaving it in a constant temperature bath at a predetermined time and a predetermined temperature.

For example, Patent Document 1 discloses an inspection method for determining the presence or absence of a minute short circuit in a power storage module in the manufacturing process of such a power storage module. The inspection method described in Patent Document 1 includes (a) a step of discharging the initially charged alkaline storage battery (storage module) to a predetermined voltage, and (b) a step of leaving the discharged alkaline storage battery for a first predetermined time. , (C) The step of measuring the voltage of the alkaline storage battery left for a first predetermined time, (d) the step of leaving the alkaline storage battery for a second predetermined time after the voltage measurement, and (e) leaving it for a second predetermined time. The step of measuring the voltage of the alkaline storage battery again, (f) the step of calculating the difference between the voltage measured in the step c and the voltage measured in the step e, and (g) the calculated voltage. It includes a step of comparing the difference with the reference value for pass / fail judgment.

Here, it is known that when the power storage module is discharged after the conditioning step, the voltage of the power storage module rises once, then turns down, and eventually converges to a predetermined voltage value. The presence or absence of a minute short circuit is the difference between the voltage value after rising (hereinafter, also referred to as "maximum voltage value") and the voltage value after convergence (hereinafter, also referred to as "converging voltage value"). It is desirable to make a judgment based on the above in terms of improving accuracy. Therefore, in the inspection method of Patent Document 1, the maximum voltage is not measured immediately after the step a but by leaving the power storage module for a first predetermined time (step c). A value is acquired, and the presence or absence of a minute short circuit is determined based on the difference between the maximum voltage value and the convergent voltage value after step d.

JP-A-2009-252459

However, after the power storage module is discharged (step a), the time until the voltage of the power storage module reaches the maximum value varies depending on the power storage module. Therefore, a relatively long time is required (in the example of Patent Document 1, 12 hours or more and 24 hours or less). In addition, the time required for the voltage to converge after the voltage of the power storage module reaches the maximum value tends to be relatively long, and may not be completely converged in the aging process. In this case, the accuracy of determining the presence or absence of a minute short circuit is lowered.

Therefore, an object of the present invention is to provide an inspection method capable of determining the presence or absence of a minute short circuit in a power storage module in a short time and with high accuracy.

The inspection method according to the present invention is an inspection method for inspecting the presence or absence of a minute short circuit in the power storage module, and is a first charging step in which the power storage module is initially charged at a predetermined charging rate and a power storage charge in the first charging step. A discharge step of discharging the SOC of the module until it reaches a predetermined first SOC, and a charge rate of the power storage module discharged in the discharge step lower than the charge rate in the first charge step, and an SOC of more than 0% 20 The second charging step of charging until the predetermined target SOC of% or less is reached, the first leaving step of leaving the power storage module charged in the second charging step for the first predetermined time, and the first leaving step of leaving. The first measurement step of measuring the voltage of the power storage module, the second leaving step of leaving the power storage module measured in the first measurement step for a second predetermined time, and the voltage of the power storage module left in the second leaving step The second measurement step to be measured includes a determination step of determining the presence or absence of a minute short circuit based on the difference between the voltage measured in the first measurement step and the voltage measured in the second measurement step.

In the above inspection method, the discharge step is carried out by carrying out the second charging step of charging until the SOC reaches a predetermined target SOC of 20% or less, which is larger than 0% and 20% or less, at a charging rate lower than that of the first charging step. It is possible to shorten the time until the voltage value in the later power storage module reaches the maximum voltage value. As a result, the time required for the inspection can be shortened because the time in the first leaving step can be shortened as compared with the case where the second charging step is not performed. Further, in the above inspection method, since a minute short circuit is determined for each power storage module based on the difference between the maximum voltage value and the convergent voltage value, it is different from other power storage modules based on the voltage value after the second leaving step. It is possible to improve the determination accuracy of a minute short circuit as compared with determining the presence or absence of a minute short circuit in a relative relationship. As a result, the presence or absence of a minute short circuit in the power storage module can be determined in a short time and with high accuracy.

In the second charging step of the inspection method according to the present invention, the power storage module may be charged with a low charging rate of 0.01 C or more and 1 C or less. As a result, it is possible to suppress that the time required for the second charging step becomes long, and at the same time, it is possible to prevent the voltage from continuing to gradually decrease due to polarization after the completion of the second charging step.

In the second charging step of the inspection method according to the present invention, the power storage module may be charged until the SOC reaches a predetermined target SOC of more than 2% and 10% or less. As a result, the difference between the voltage measured in the first measurement step and the voltage measured in the second measurement step when the SOC decreases due to the minute short circuit is appropriately secured, so that it is easy to determine the presence or absence of the minute short circuit. It becomes.

In the first charging step of the inspection method according to the present invention, the first discharging step of discharging the power storage module charged in the first charging step to the first SOC and the first discharging step performed after the first discharging step are performed to make the power storage module first. It may include an additional discharge step of discharging to a second SOC lower than the SOC. In this inspection method, the SOC of the power storage module before the second charging process can be brought close to 0%, and the target SOC (predetermined target SOC) can be charged more accurately in the second charging process. ..

According to the present invention, the presence or absence of a minute short circuit in the power storage module can be determined in a short time and with high accuracy.

It is a schematic sectional drawing which shows the power storage device which includes the power storage module which is inspected by the inspection method which concerns on one Embodiment. It is schematic cross-sectional view which shows the power storage module which is inspected by the inspection method which concerns on one Embodiment. It is a flowchart of the inspection method which concerns on one Embodiment. It is a graph which showed the change of the voltage drop in the power storage module after discharge. It is a graph which showed the change of the voltage drop in the power storage module after discharge. It is a graph which showed the change of the voltage in the power storage module after the additional charge. It is a graph which showed the change of the voltage value at the time of discharging the power storage module of FIG.

Hereinafter, one embodiment will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate description is omitted.

First, an example of the power storage device 1 inspected in the inspection method according to the embodiment will be described mainly with reference to FIGS. 1 and 2. The power storage device 1 is used as a battery for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. As shown in FIGS. 1 and 2, the power storage device 1 has a module laminated body 2 including a plurality of stacked power storage modules 4 and a restraining load on the module laminated body 2 in the stacking direction D1 of the module laminated body 2. The restraint member 3 to which the above is added is provided.

The module laminate 2 includes a plurality of power storage modules 4 and a plurality of conductive plates 5. The power storage module 4 is a bipolar battery and has a rectangular shape when viewed from the stacking direction D1. The power storage module 4 is, for example, a secondary battery such as a nickel hydrogen secondary battery or a lithium ion secondary battery, or an electric double layer capacitor. In the following description, a nickel hydrogen secondary battery will be illustrated.

The power storage modules 4 adjacent to each other in the stacking direction D1 are electrically connected to each other via the conductive plate 5. Here, the power storage modules 4 are arranged at the laminated ends of the module laminate 2, and the conductive plates 5 are arranged between the power storage modules 4 adjacent to each other in the stacking direction D1. A conductive plate P different from the conductive plate 5 is arranged outside the stacking direction of the power storage module 4 located at the laminated end. A positive electrode terminal 6 is connected to one conductive plate P, and a negative electrode terminal 7 is connected to the other conductive plate P. The positive electrode terminal 6 and the negative electrode terminal 7 are drawn out from the edge of the conductive plate P, for example, in a direction intersecting the stacking direction D1. The positive electrode terminal 6 and the negative electrode terminal 7 charge and discharge the power storage device 1.

Inside the conductive plates 5 arranged between the power storage modules 4, a plurality of flow paths 5a through which a cooling medium such as air is circulated are provided. The flow path 5a extends along a direction that intersects (orthogonally), for example, the stacking direction D1 and the pull-out direction of the positive electrode terminal 6 and the negative electrode terminal 7. The conductive plate 5 has a function as a connecting member that electrically connects the power storage modules 4 to each other. Further, the conductive plate 5 also has a function as a heat radiating plate that dissipates heat generated by the power storage module 4 by circulating a refrigerant through these flow paths 5a. In the example of FIG. 1, the area of the conductive plate 5 seen from the stacking direction D1 is smaller than the area of the power storage module 4, but from the viewpoint of improving heat dissipation, the area of the conductive plate 5 is the power storage module 4. It may be the same as the area of the power storage module 4 and may be larger than the area of the power storage module 4.

The restraint member 3 is composed of a pair of end plates 8 that sandwich the module laminate 2 in the stacking direction D1, and fastening bolts 9 and nuts 10 that fasten the end plates 8 to each other. The end plate 8 is a rectangular metal plate having an area one size larger than the areas of the power storage module 4, the conductive plate 5, and the conductive plate P as viewed from the stacking direction D1. A plate-shaped or film-shaped insulating member F having electrical insulation is provided on the surface of the end plate 8 on the module laminate 2 side. The insulating member F insulates between the end plate 8 and the conductive plate P.

The edge 8b of the end plate 8 is provided with an insertion hole 8a at a position outside the module laminate 2. The fastening bolt 9 is inserted from the insertion hole 8a of one end plate 8 toward the insertion hole 8a of the other end plate 8. A nut 10 is screwed into the tip portion of the fastening bolt 9 protruding from the insertion hole 8a of the other end plate 8. As a result, the power storage module 4, the conductive plate 5, and the conductive plate P are sandwiched by the end plates 8 and unitized as the module laminate 2. Further, in the module laminate 2, a restraining load is applied to the stacking direction D1 by the end plates 8 and 8.

Next, the configuration of the power storage module 4 will be described in detail. As shown in FIG. 2, the power storage module 4 includes an electrode laminate 11 and a resin sealant 12 that seals the electrode laminate 11. The electrode laminate 11 is composed of a plurality of electrodes laminated along the stacking direction D1 of the power storage module 4 via the separator 13. These electrodes include a plurality of bipolar electrodes 14, a negative electrode termination electrode 18, and a positive electrode termination electrode 19.

The bipolar electrode 14 includes a metal plate 15 including one surface 15a and the other surface 15b on the opposite side of the one surface 15a, a positive electrode 16 provided on the one surface 15a, and a negative electrode 17 provided on the other surface 15b. doing. The positive electrode 16 is formed by applying a positive electrode active material to a metal plate 15. Examples of the positive electrode active material constituting the positive electrode 16 include nickel hydroxide. The negative electrode 17 is formed by applying the negative electrode active material to the metal plate 15. Examples of the negative electrode active material constituting the negative electrode 17 include a hydrogen storage alloy.

In the present embodiment, the formation region of the negative electrode 17 on the other surface 15b of the metal plate 15 is slightly larger than the formation region of the positive electrode 16 on the one surface 15a of the metal plate 15. In the electrode laminate 11, the positive electrode 16 of one bipolar electrode 14 faces the negative electrode 17 of another bipolar electrode 14 adjacent to one of the stacking directions D1 with the separator 13 interposed therebetween. In the electrode laminate 11, the negative electrode 17 of one bipolar electrode 14 faces the positive electrode 16 of another bipolar electrode 14 adjacent to the other in the stacking direction D1 with the separator 13 interposed therebetween.

The negative electrode terminal electrode 18 has a metal plate 15 and a negative electrode 17 provided on the other surface 15b of the metal plate 15. The negative electrode terminal electrode 18 is arranged at one end of the stacking direction D1 so that the other surface 15b faces the center side of the stacking direction D1 in the electrode laminated body 11. One surface 15a of the metal plate 15 of the negative electrode terminal electrode 18 constitutes one outer surface in the stacking direction D1 of the electrode laminate 11, and one conductive plate 5 or conductive plate P adjacent to the power storage module 4 (see FIG. 1). ) Is electrically connected. The negative electrode 17 provided on the other surface 15b of the metal plate 15 of the negative electrode terminal electrode 18 faces the positive electrode 16 of the bipolar electrode 14 at one end in the stacking direction D1 via the separator 13.

The positive electrode terminal electrode 19 has a metal plate 15 and a positive electrode 16 provided on one surface 15a of the metal plate 15. The positive electrode terminal electrode 19 is arranged at the other end of the stacking direction D1 so that one surface 15a faces the center side of the stacking direction D1 in the electrode laminated body 11. The positive electrode 16 provided on one surface 15a of the positive electrode terminal electrode 19 faces the negative electrode 17 of the bipolar electrode 14 at the other end in the stacking direction D1 via the separator 13. The other surface 15b of the metal plate 15 of the positive electrode terminal electrode 19 constitutes the other outer surface in the stacking direction D1 of the electrode laminate 11, and the other conductive plate 5 or the conductive plate P adjacent to the power storage module 4 (see FIG. 1). ) Is electrically connected.

The metal plate 15 is made of, for example, a nickel plate whose surface is plated, a steel plate whose surface is plated, or the like. Here, the metal plate 15 is made of a plated steel plate obtained by plating the surface of the steel plate with nickel. As the steel sheet used as the base material of the plated steel sheet, for example, ordinary steel such as rolled steel or special steel such as stainless steel is used. The edge portion 15c of the metal plate 15 has a rectangular frame shape, and is an uncoated region in which the positive electrode active material and the negative electrode active material are not coated.

The separator 13 is formed in a sheet shape, for example. Examples of the separator 13 include a porous film made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP), a woven fabric made of polypropylene, methyl cellulose and the like, or a non-woven fabric. The separator 13 may be reinforced with a vinylidene fluoride resin compound.

The sealing body 12 is formed in a rectangular tubular shape as a whole by, for example, an insulating resin. The sealing body 12 is provided on the side surface 11a of the electrode laminate 11 so as to surround the edge portion 15c of the metal plate 15. The sealing body 12 holds the edge portion 15c on the side surface 11a. The sealing body 12 extends to the side surface 11a along the stacking direction D1 with the plurality of first sealing portions 21 bonded to the edge portion 15c of the metal plate 15, and is bonded to each of the first sealing portions 21. It has a second sealing portion 22. The first sealing portion 21 and the second sealing portion 22 are made of an insulating resin having alkali resistance. Examples of the constituent materials of the first sealing portion 21 and the second sealing portion 22 include polypropylene (PP), polyphenylene sulfide (PPS), modified polyphenylene ether (modified PPE), and the like.

The first sealing portion 21 is continuously provided on one surface 15a of the metal plate 15 over the entire circumference of the edge portion 15c, and has a rectangular frame shape when viewed from the stacking direction D1. In the present embodiment, the first sealing portion 21 is provided not only on the metal plate 15 of the bipolar electrode 14, but also on the metal plate 15 of the negative electrode terminal 18 and the metal plate 15 of the positive electrode 19. In the negative electrode terminal electrode 18, the first sealing portion 21 is provided on the edge portion 15c of the one surface 15a of the metal plate 15, and in the positive electrode termination electrode 19, both the edge portions of both the one surface 15a and the other surface 15b of the metal plate 15 are provided. The first sealing portion 21 is provided on the 15c.

The first sealing portion 21 is overlapped with the edge portion 15c of the metal plate 15 to form an overlapping portion K. In the overlapping portion K, the first sealing portion 21 is airtightly welded to the metal plate 15 by, for example, ultrasonic waves or thermocompression bonding. The first sealing portion 21 is formed by using, for example, a film having a predetermined thickness in the stacking direction D1. The inside of the first sealing portion 21 is located between the edge portions 15c of the metal plates 15 adjacent to each other in the stacking direction D1. The outside of the first sealing portion 21 projects outward from the edge of the metal plate 15, and the tip portion thereof is held by the second sealing portion 22. The first sealing portions 21 adjacent to each other along the stacking direction D1 may be separated from each other or may be in contact with each other. Further, the outer edge portions of the first sealing portion 21 may be bonded to each other by, for example, hot plate welding.

In the electrode laminate 11, a step portion 23 for mounting the edge portion of the separator 13 is provided on the inner edge side of the first sealing portion 21 located in the inner layer in the stacking direction D1. The step portion 23 may be formed by folding back the outer edge portion of the film constituting the first sealing portion 21 inward. The step portion 23 may be formed by superimposing the film forming the upper stage on the film forming the lower stage.

The second sealing portion 22 is provided outside the electrode laminate 11 and the first sealing portion 21, and constitutes an outer wall (housing) of the power storage module 4. The second sealing portion 22 is formed, for example, by injection molding of a resin, and extends along the stacking direction D1 over the entire length of the electrode laminate 11. The second sealing portion 22 has a rectangular frame shape extending in the axial direction in the stacking direction D1. The second sealing portion 22 is welded to the outer edge portion of the first sealing portion 21 by heat during injection molding, for example.

The second sealing portion 22 has overhang portions 24 at both ends in the stacking direction D1. One overhang portion 24 projects toward the inner edge side of the first sealing portion 21 at one end in the stacking direction D1 and is welded to the one surface 15a side of the metal plate 15 constituting the negative electrode terminal electrode 18. It is connected to the part 21. The other overhang portion 24 projects toward the inner edge side of the first sealing portion 21 at the other end of the stacking direction D1 and is welded to the other surface 15b side of the metal plate 15 constituting the positive electrode terminal electrode 19. It is connected to the stop portion 21. The overhang lengths of one and the other overhang portions 24 are equal to each other, and the tips 24a of these overhang portions 24 overlap the metal plate 15 and the first sealing portion 21 when viewed from the stacking direction D1. It is located so as to overlap the portion K.

The first sealing portion 21 and the second sealing portion 22 form an internal space V between adjacent electrodes and seal the internal space V. More specifically, the second sealing portion 22, together with the first sealing portion 21, is between the bipolar electrodes 14 adjacent to each other along the stacking direction D1 and the negative electrode termination electrodes 18 adjacent to each other along the stacking direction D1. And the bipolar electrode 14 and between the positive electrode terminal electrode 19 and the bipolar electrode 14 adjacent to each other along the stacking direction D1 are sealed. As a result, an airtightly partitioned internal space V is formed between the adjacent bipolar electrodes 14, between the negative electrode terminal 18 and the bipolar electrode 14, and between the positive electrode 19 and the bipolar electrode 14. ing. An aqueous electrolytic solution (not shown) containing an alkaline solution such as an aqueous potassium hydroxide solution is housed in the internal space V. The electrolytic solution is impregnated in the separator 13, the positive electrode 16, and the negative electrode 17.

When the first sealing portion 21 is welded to the metal plate 15, the surface of the metal plate 15 described above is roughened by, for example, electrolytic plating. The roughening may be performed on the surface of the metal plate 15 to which at least the first sealing portion 21 is welded. In the present embodiment, with respect to the metal plate 15 constituting the bipolar electrode 14 and the metal plate 15 constituting the negative electrode terminal electrode 18, only one surface 15a needs to be roughened, and the metal constituting the positive electrode terminal electrode 19 needs to be roughened. As for the plate 15, it is sufficient that both the one surface 15a and the other surface 15b are roughened.

Next, an example of the inspection method of the power storage module 4 will be described mainly with reference to FIG. As shown in FIG. 3, the inspection method of the present embodiment includes a first charging step S1, a discharging step (first discharging step) S2, an additional discharging step S3, a second charging step S4, and a first leaving. A step S5, a first measurement step S6, a second leaving step S7, a second measurement step S8, and a determination step S9 are included.

The first charging step S1 is a step called a conditioning step in which the power storage module 4 is initially charged. In the first charging step S1, discharging to a predetermined SOC (state of charge) (hereinafter referred to as “first SOC”) and charging to a predetermined SOC (hereinafter referred to as “third SOC”) are performed. This is a process in which and is performed at least once. In the present embodiment, the power storage module 4 is repeatedly charged and discharged (for example, 10 times) between the first SOC and the third SOC, and finally charged to the third SOC. Examples of the first SOC are 0% to 20%, and examples of the third SOC are 70% to 160%.

The discharging step S2 is a step of discharging the power storage module 4 charged by the first charging step S1 to the first SOC (predetermined SOC). In the discharging step S2, for example, the power storage module 4 is discharged at a charging rate of 1C to 5C. The additional discharge step S3 is a step that is carried out following the discharge step S2 and discharges the power storage module 4 so as to have a second SOC that is even lower than the first SOC. The additional discharge step S3 discharges the power storage module 4 at a charging rate of, for example, 0.1C to 1C.

In the second charging step S4, the power storage module 4 discharged in the additional discharging step S3 has a charging rate lower than that of the first charging step S1 and has a SOC of more than 0% and a predetermined target SOC of 20% or less. It is a process of charging until it becomes. In the second charging step S4, for example, the power storage module 4 is charged at a low charging rate of 0.01C or more and 1C or less. In the charging in the second charging step S4, the SOC is preferably 2% or more and 10% or less, and the SOC is more preferably 3% or more and 5% or less.

The first leaving step S5 is a step of leaving the power storage module 4 charged in the second charging step S4 for a first predetermined time. The leaving in the first leaving step S5 is a time for securing a time until the voltage value rising due to polarization turns to falling after the completion of the second charging step S4 and the rate of falling becomes a certain value or less. In the first leaving step S5, for example, the power storage module 4 is left at room temperature (for example, 15 ° C. to 30 ° C.) for 0.2 (hr) to 1 (hr).

The first measurement step S6 is a step of measuring the voltage of the power storage module 4 left in the first leaving step S5. The measurement of the power storage module 4 in the first measurement step S6 is performed using a known device.

The second leaving step S7 is a step of leaving the power storage module 4 measured in the first measuring step S6 for a second predetermined time. The second leaving step S7 is a step of dissolving foreign substances that may be mixed in the positive electrode in the electrolytic solution and reprecipitating them in the negative electrode at the same time as aging (activation of the negative electrode active material). Specifically, in the second leaving step S7, for example, the power storage module 4 measured in the first measurement step S6 is put into a constant temperature bath at 25 ° C. to 70 ° C., and for example, 24 (hr) to 168. During (hr), the power storage module 4 is left unattended. It should be noted that the constant temperature bath is not provided with a device for measuring the voltage of the power storage module 4.

The second measurement step S8 is a step of measuring the voltage of the power storage module 4 left in the second leaving step S7. The measurement of the power storage module 4 in the second measurement step S8 is performed using a known device.

The determination step S9 determines the presence or absence of a minute short circuit based on the difference between the voltage measured in the first measurement step S6 and the voltage measured in the second measurement step S8 (hereinafter, simply referred to as “voltage difference”). This is the judgment process. Specifically, based on a predetermined threshold value, if the voltage difference is larger than the threshold value, it is determined that the power storage module 4 has a minute short circuit, and if the voltage difference is equal to or less than the threshold value, the power storage module 4 has. Judge that there is no minute short circuit.

Next, it will be described by the following examples that the presence or absence of a minute short circuit in the power storage module can be determined in a short time and with high accuracy by the inspection method of the present embodiment. An embodiment of the present embodiment will be described. The present invention is not limited to the following examples.

First, the power storage module 4 described in the upper part was prepared. Next, the power storage module 4 was repeatedly charged and discharged while the SOC was between 5% and 90% (first charging step S1). Next, the power storage module 4 was discharged until the SOC became about 3% (discharge step S2). More specifically, the power storage module 4 was discharged at 4C. Next, the power storage module 4 was discharged until the SOC of the discharged power storage module 4 became 0% (second SOC), which is even lower than 3% (first SOC) (additional discharge step S3). More specifically, the power storage module 4 was discharged at 0.4 C.

Next, the power storage module 4 was charged with a charging rate of 0.1 C until the SOC (predetermined SOC) became 3% (second charging step S4). Here, the time required for the second charging step was 0.3 (hr). Next, the power storage module 4 was left for 0.7 (hr) (first leaving step S5). In this period, after the end of the second charging step S4, the voltage value rising due to polarization turned downward, and then the ratio of the voltage falling with respect to the passage of time became constant or less, and the voltage became stable. In the power storage module 4 of this embodiment, the rate of decrease became less than a certain level when 0.5 (hr) had passed after being left unattended. That is, the voltage between the terminals of the power storage module 4 became stable. Next, the voltage of the power storage module 4 in which the rate of decrease was below a certain level was measured (first measurement step S6).

Next, the power storage module 4 was put into a constant temperature bath whose temperature was adjusted to 50 ° C., and the power storage module 4 was left for 48 (hr), for example (second leaving step S7). Then, after 48 (hr), the voltage of the power storage module 4 was measured (second measurement step S8). Finally, the presence or absence of a minute short circuit was determined based on the difference between the voltage measured in the first measurement step S6 and the voltage measured in the second measurement step S8. Specifically, based on a predetermined threshold value (for example, 1.5V), if the voltage difference is larger than the threshold value, it is determined that the power storage module 4 has a minute short circuit, and the voltage difference is equal to or less than the threshold value. If so, it is determined that the power storage module 4 does not have a minute short circuit.

In the method shown in Patent Document 1, in order to obtain the maximum value of the voltage which is the reference voltage for observing the voltage change for each individual module, 12 (hr) or more and 24 (hr) or less after the discharge step S2. Although it took time, in the inspection method of this embodiment, it is possible to acquire a stable voltage value which is a reference voltage for observing the voltage change of each module in an extremely short time of 1 (hr). It will be possible. It is considered that this is because the hydrogen ion concentration distribution generated in the discharge step / additional discharge step can be eliminated in an extremely short time by carrying out the second charging step S4.

Next, the action and effect of the above embodiment will be described. L1 and L2 of FIG. 4 are diagrams showing changes in the voltage of the power storage module 4 after the second charging step S4 of the above embodiment. L1 indicates the power storage module 4 determined to be “without a minute short circuit”, and L2 indicates the power storage module 4 determined to be “with a minute short circuit”.

As will be described in detail later, L3 and L4 in FIG. 4 show changes in the voltage of the power storage module 4 after the discharge step S2 when the second charging step S4 is not performed. As shown in L3 and L4 of FIG. 4, when the power storage module 4 is discharged after the initial charging (conditioning), the voltage of the power storage module 4 once rises and then turns down, and then the rate of fall becomes gradual, and then It was known that it would converge. L3 and L4 of FIG. 4 show an example of the voltage drop due to such self-discharge and minute short circuit.

In the conventional inspection method, after discharging the power storage module 4, the power storage module 4 is housed in a constant temperature bath and left to stand (aging step), and after the aging process is completed, the power storage module 4 is taken out from the constant temperature bath and the voltage value is measured. , The measured value was used as a determination factor for the presence or absence of a minute short circuit. In this inspection method, the voltages of a plurality of power storage modules 4 are measured, and an individual having a measurement value that greatly deviates from the plurality of measured values is determined to have a slight short circuit or compared with a preset threshold value. Individuals whose voltage was lower than the threshold value were judged to have a slight short circuit. In the determination based on the relative relationship of the plurality of power storage modules 4, the variation among individuals was not taken into consideration, and the determination accuracy could not be improved. As a method for improving the determination accuracy, it is conceivable not only to acquire the voltage value after the aging step but also to measure the change in the voltage in the aging step for each individual. However, a voltage measuring device is not provided inside the constant temperature bath used in the aging process in order to reduce costs, which is not realistic.

On the other hand, as in Patent Document 1 described above, after discharging the initially charged power storage module 4, the module 4 is left until it reaches the maximum voltage value, and after obtaining the voltage value at that time, it is left in a constant temperature bath. Has been proposed. FIG. 5 is a graph showing the results of measuring the voltage transition after discharging for the plurality of power storage modules 4. As shown in FIG. 5, the time required for the discharged power storage module 4 to reach the maximum voltage value varies depending on the power storage module 4. Occasionally, it may take 20 hours or more for the discharged power storage module 4 to reach the maximum voltage value. Therefore, although the determination accuracy can be improved by this inspection method, the inspection time becomes long.

Therefore, in the inspection method of the present embodiment, the second charging is performed by charging at a charging rate lower than the charging rate in the first charging step S1 until the SOC is greater than 0% and 20% or less, which is a predetermined target SOC. Step S4 is being carried out. As a result, it is possible to shorten the time until the power storage module 4 reaches the maximum voltage value after the discharge step S2 (additional discharge step S3). Specifically, as shown in L1 and L2 of FIG. 4, the time to the point P11 and the point P21 is shorter than that of the conventional inspection method (point P31 of L3 and point P41 of L4 in FIG. 4). can do. Therefore, as compared with the case where the second charging step S4 is not performed, the time in the first leaving step S5 can be shortened, so that the time required for the inspection can be shortened.

When the second charging step S4 is carried out, as shown in FIG. 6, the battery voltage drops from the voltage at the end of charging (H portion shown in FIG. 6) due to polarization. In the present embodiment, the change in the battery voltage from the end of charging is observed, and the voltage at points P5 and P6 where the rate of the voltage drop is 0 or the minimum is defined as the maximum voltage value of the battery. ing. FIG. 6 is a diagram showing a change in the voltage value of the power storage module 4 after the second charging step S4. L5 of FIG. 6 shows the change in the voltage value of the power storage module charged until the SOC reaches 3% in the second charging step S4, and L6 shows the change in the voltage value of the power storage module 4 charged until the SOC reaches 5%.

Further, in the inspection method of the present embodiment, by carrying out the second charging step S4, the width of the voltage drop due to the self-discharge of the normal battery in the second leaving step S7 becomes smaller. Therefore, the normal determination value (voltage drop amount) in the determination step S9 after the end of the second leaving step S7 can be set as a narrow range. As a result, the determination accuracy between the abnormality and the normal in the determination step S9 is improved.

In the conventional inspection method, the presence or absence of a minute short circuit is determined based on the voltage value measured at the end of the aging step (second leaving step S7). Therefore, for example, a high voltage value is set with respect to a preset threshold value. There is a possibility that the individual L4 shown is determined to be "without a minute short circuit", and the individual L3 showing a low voltage value with respect to the threshold value is determined to be "with a minute short circuit". However, L4 determined to have "no minute short circuit" has a large voltage difference between the maximum voltage value P41 and the voltage value N2 after the aging process, and is originally a power storage module that should be determined to have "with minute short circuit". L3, which is 4 and is determined to have "small short circuit", has a small voltage difference between the maximum voltage value P31 and the voltage value G2 after the aging process, and is originally determined to be "without minute short circuit". Power storage module 4. As described above, the conventional inspection method cannot make a judgment in consideration of the variation among individuals. In the inspection method of the present embodiment, the voltages before and after the aging step are acquired for each individual and the determination is made based on the difference, so that the possibility of erroneous determination is reduced. This makes it possible to improve the inspection accuracy. In the present embodiment, the inspection accuracy can be improved by acquiring the accurate voltage drop amount in the second leaving step S7, and in addition to the addition of such an element, the accuracy can be further improved.

Further, in the second charging step S4 in the inspection method of the present embodiment, charging is performed up to a predetermined target SOC in which the SOC is larger than 0% and 20% or less. Here, the upper limit is set to 20% for the following reasons. FIG. 7 shows a change (voltage curve) in the voltage value when the power storage module 4 is discharged. As shown in FIG. 7, the power storage module 4 inspected in the above embodiment tends to have a small voltage drop when the SOC decreases when the SOC exceeds 20%. Therefore, when the SOC is charged to exceed 20%, it becomes difficult to detect the voltage difference even if the voltage drops due to a minute short circuit. In this respect, in the second charging step S4 of the present embodiment, since the SOC is set to 20% or less, it becomes easy to detect that there is a voltage drop due to a minute short circuit.

Further, in the second charging step in the inspection method of the above embodiment, the power storage module 4 is charged at a charging rate of 0.01 C or more and 1 C or less. As a result, it is possible to suppress the lengthening of the time required for the second charging step S4 and to prevent the voltage from continuing to gradually decrease due to polarization after the completion of the second charging step S4.

Although one embodiment has been described in detail above, the present invention is not limited to the above embodiment.

In the above embodiment, an example of carrying out the additional discharge step S3 has been described, but the step may be omitted.

In the above embodiment, the example of inspecting the power storage module 4 configured as a nickel-metal hydride secondary battery has been described, but it can also be applied to a power storage module configured as a lithium ion secondary battery.

1 ... Power storage device, 4 ... Power storage module, S1 ... First charging process, S2 ... Discharging process (first discharging process), S3 ... Additional discharging process, S4 ... Second charging process, S5 ... First leaving process, S6 ... First measurement step, S7 ... second leaving step, S8 ... second measurement step, S9 ... judgment step.

Claims (4)

This is an inspection method for inspecting the presence or absence of minute short circuits in the power storage module.
The first charging step of initial charging the power storage module at a predetermined charging rate, and
A discharge step of discharging the SOC of the power storage module charged in the first charge step until it reaches a predetermined first SOC,
The electricity storage module discharged in the discharging step is charged at a charging rate lower than the charging rate in the first charging step until the SOC reaches a predetermined target SOC of more than 0% and 20% or less. Two charging processes and
In the first leaving step of leaving the power storage module charged in the second charging step for a first predetermined time,
The first measurement step of measuring the voltage of the power storage module left in the first leaving step, and
A second leaving step in which the power storage module measured in the first measuring step is left for a second predetermined time, and a second leaving step.
The second measurement step of measuring the voltage of the power storage module left in the second leaving step, and
An inspection method including a determination step of determining the presence or absence of the minute short circuit based on the difference between the voltage measured in the first measurement step and the voltage measured in the second measurement step. The inspection method according to claim 1, wherein in the second charging step, the power storage module is charged at a low charging rate of 0.01 C or more and 1 C or less. The inspection method according to claim 2, wherein in the second charging step, the power storage module is charged until the SOC reaches the predetermined target SOC of more than 2% and 10% or less. The discharge step is carried out after the first discharge step of discharging the power storage module charged in the first charge step to the first SOC and the first discharge step, and the power storage module is discharged from the first SOC. The inspection method according to any one of claims 1 to 3, comprising an additional discharge step of discharging to a second SOC which is also low.

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