JP2004152732A - Airtightness inspection method for sealed cell and its instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an airtightness inspection method for a sealed cell which is quickly, simply and inexpensively performed. <P>SOLUTION: By holding the sealed cell to be inspected in a pressurized gas atmosphere, the gas is made to enter the interior of the cell having airtight defects such as pinholes. Then, by reducing the gas pressure, the internal pressure of the cell is caused to be higher than the environment gas pressure, whereby the cell is caused to dilate. Then, by measuring the cell dimension and comparing with a dimensional standard, airtight defects are detected and judged as dimensional abnormality. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an airtightness inspection method and an airtightness inspection device for a sealed battery that can be implemented quickly, simply, and inexpensively.
[0002]
[Prior art]
It is extremely important to maintain the airtightness of a sealed battery from the viewpoint of storage characteristics and safety of the battery.
[0003]
For example, when the airtightness of primary batteries such as alkaline manganese batteries is not sufficiently maintained, the alkaline aqueous solution, which is an electrolytic solution, leaks out of the battery case when stored for a long time, and a predetermined discharge capacity is secured when the batteries are used. It may not be possible. If the electrolyte leaks while the battery is mounted on the device, the device may be discolored or corroded.
[0004]
The problem is even more serious when the battery used is a secondary battery such as a lithium ion battery or a nickel hydride battery. Since secondary batteries are recharged after being discharged and used repeatedly, they tend to be used for a longer period than primary batteries. If the airtightness of the battery is not maintained sufficiently, leakage of the electrolyte occurs, which greatly affects the cycle life characteristics. In general, a secondary battery tends to be more expensive than a primary battery having the same amount of energy, so that the economic loss due to a decrease in battery performance tends to increase.
[0005]
As described above, it is extremely important to maintain the airtightness of a sealed battery in order to maintain the performance of the battery for a long period of time and to prevent damage to equipment due to liquid leakage. It is necessary to carry out an airtight inspection to eliminate defective products that are not sufficiently airtight. Therefore, various airtightness inspection methods for sealed batteries have been proposed.
[0006]
For example, Patent Literature 1 proposes a method in which air in a battery case is replaced with a test gas, and a gas sensor detects a test gas leaking from a poorly-sealed portion. However, in this method, replacement of gas is troublesome, and one battery requires one gas sensor. For this reason, a large number of gas sensors are required to perform the inspection in a large amount and quickly. As a result, a large amount of capital investment is required, and the economic burden is large.
[0007]
Further, in Patent Document 2, in order to inspect the airtightness of a sealed electric device, a sealed container accommodating the sealed electric device, a means for pressurizing or depressurizing the inside of the sealed container, and a difference for detecting a pressure in the sealed container are described. There has been proposed an inspection apparatus including a pressure sensor and a unit for determining the presence / absence of air circulation inside and outside a sealed electric device case. However, the method adopted here requires a high-precision differential pressure sensor in order to detect the air flow at the location of poor airtightness. In addition, one airtight container is required for one electric device.
[0008]
As described above, the conventional airtight inspection method cannot be performed quickly, simply, and inexpensively.
[0009]
[Patent Document 1]
JP-A-5-21089 [Patent Document 2]
JP-A-62-38338
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for quickly, easily and inexpensively performing an airtight inspection of a sealed battery.
[0011]
[Means for Solving the Problems]
According to the present invention, a sealed battery is housed in a sealed container, a first step of maintaining the sealed battery under a pressurized gas atmosphere, a second step of reducing the gas pressure in the sealed container, and measuring the dimensions of the battery. And a third step of determining whether the airtightness is good or bad by comparing the airtightness with a standard size.
[0012]
If the battery has pinholes or minute cracks, the gas enters the battery by holding it in a pressurized gas atmosphere in the first step. At this time, since the battery internal pressure is equal to or less than the outside of the battery, the battery does not expand. Then, when the gas in the sealed container is discharged in the second step to reduce the atmospheric pressure outside the battery, for example, when the pressurized gas is released and the internal pressure of the sealed container is returned to normal pressure, Gas entering the battery is released through pinholes or cracks, but at a relatively slow rate. Therefore, the internal pressure of the battery temporarily becomes higher than the atmospheric pressure outside the battery. This causes the battery to expand, and pinholes or cracks are detected in the third step by measuring the size of the battery and comparing it to a standard size. That is, the presence or absence of a pinhole or a crack can be detected as a dimensional abnormality.
[0013]
If the sealed battery has no pinholes or minute cracks, the gas does not enter the battery in the first step, so that the battery does not expand in the second step and no dimensional change occurs. Here, the purpose of measuring the dimensions of the battery is to grasp the change from the initial dimensions (especially, the presence or absence of expansion) and thereby determine the presence or absence of poor airtightness. No need to know. Therefore, instead of measuring the absolute value of the dimension, for example, a method of grasping the presence or absence of expansion based on whether or not the battery can pass through a slit having a gap having the same dimension as the standard dimension may be adopted.
[0014]
The gas is preferably one selected from the group consisting of air, nitrogen, argon, helium, carbon dioxide and water vapor, or a mixture of two or more. Since it is the gist of the present invention to cause the expansion of the battery by injecting the gas into the battery, it is not preferable that the gas is consumed in the battery. For example, it is not preferable to use hydrogen or oxygen as the gas when performing an airtight inspection of a sealed nickel-metal hydride storage battery. This is because the hydrogen storage alloy used for the negative electrode of the nickel-metal hydride storage battery absorbs or consumes hydrogen or oxygen. From such a viewpoint, it is preferable to use an inert gas or a gas that promotes expansion of the battery.
[0015]
Further, the present invention provides a first step of holding at least a part of the sealed battery in a pressurized liquid, a second step of reducing the pressure, and measuring the size of the battery and comparing the measured size with the standard size. And a third step of determining whether the airtightness is good or not. Here, the part of the sealed battery held in the pressurized liquid is a part to be inspected, specifically, a part joined by, for example, laser welding or a sealing part. The liquid is preferably water or an aqueous solution.
[0016]
In the case where the battery has pinholes or minute cracks, a liquid, for example, water enters the battery when held in the pressurized liquid in the first step. If the battery used for inspection is a lithium battery, lithium ion secondary battery, etc., and the negative electrode is at least partially charged, water that has entered the battery immediately reacts with the negative electrode to generate hydrogen gas. Let it. While the rate of gas generation is relatively high, the rate at which gas is released from pinholes and minute cracks is relatively low. A significantly higher state is realized temporarily. This causes the battery to expand. Thereafter, in a third step, the presence or absence of a pinhole or a crack is determined by grasping the dimensional change of the battery.
[0017]
If the negative electrode is in a completely uncharged state before the battery is first charged, water in the battery is electrolyzed at the first charge to generate oxygen gas and hydrogen gas. Expansion is caused. Therefore, in this case, the presence or absence of a pinhole or a crack is determined by measuring the dimensions of the battery after the first charge.
[0018]
If the battery has pinholes or minute cracks, the thickness of the battery changes if the battery is square, and the height of the battery changes if the battery is cylindrical. Therefore, the presence or absence of pinholes or cracks is determined by measuring the thickness and height of these and comparing them with standard dimensions.
[0019]
In the first step, when the liquid is kept under pressure in the liquid, the liquid is preferably water or an aqueous solution. However, when the sealed battery to be inspected is a lithium ion secondary battery, the liquid is preferably For example, an aqueous solution of sodium carbonate or lime water may be used. This is because the electrolyte solution of the lithium ion secondary battery may react with water to generate hydrofluoric acid, which may leak out of the battery in the inspection process and corrode peripheral devices and equipment. If an aqueous solution of sodium carbonate or lime water is used as the liquid, the hydrofluoric acid can be rendered harmless.
[0020]
In the present invention, when the sealed battery is kept under gas or liquid pressure, the pressure is preferably 0.15 MPa or more and 1.0 MPa or less. Further, the time and temperature for holding under pressure are desirably from 60 seconds to 2 hours and from 20 ° C to 60 ° C, respectively.
[0021]
If the pressure is lower than 0.15 MPa when holding under pressure, the gas or liquid does not sufficiently enter the battery, and as a result, the inspection accuracy decreases. If the pressure is higher than 1.0 MPa, the applied pressure may deform even non-defective batteries without pinholes or cracks. Note that the pressing force needs to be determined in consideration of the operating pressure of the safety valve mounted on the battery, and the pressing force needs to be set lower than the operating pressure of the safety valve. If the time of holding under pressure is shorter than 60 seconds, the gas or liquid does not sufficiently enter the battery, and as a result, the inspection accuracy is reduced. If the time of holding under pressure is longer than 2 hours, there is a possibility that a non-defective battery without pinholes or cracks may be deformed. From the viewpoint of performing the inspection quickly, the time during which the pressure is maintained under pressure is preferably as short as possible as long as the inspection accuracy is not reduced, and more preferably 10 minutes or less.
[0022]
In addition, when the atmosphere temperature when maintaining the pressurized gas atmosphere is 20 ° C. or less, moisture in the air may condense on the battery during or after the inspection. Even if dew condensation occurs, there is no problem in the inspection itself, but a separate process such as wiping off moisture is required. If the ambient temperature is 60 ° C. or higher, the battery is heated in the inspection process, which may adversely affect battery characteristics.
[0023]
Furthermore, when the temperature held in the pressurized liquid is 20 ° C. or less, the liquid may freeze with a change in the pressure in the sealed container. The liquid may suddenly boil with the pressure change.
[0024]
In addition, when the pinhole to be detected is blocked by an electrolyte salt or the like derived from the electrolyte in the battery, the inspection accuracy may be reduced. In this case, by keeping the electrolyte salt in pressurized water, the dissolution of the electrolyte salt can be promoted, and a decrease in inspection accuracy can be prevented. From the viewpoint of accelerating the dissolution of the electrolyte salt, the water temperature is more preferably 30 ° C. or more and 50 ° C. or less. In the first step, the dissolution of the electrolyte salt can be promoted by stirring the pressurized liquid or by applying ultrasonic vibration to the liquid or the sealed container.
[0025]
In reducing the pressure in the second step, the speed is preferably 0.1 MPa / sec or more. If the pressure is reduced at a lower speed, the speed at which the gas or liquid that has entered the battery at the time of pressurization is released from the pinhole may follow the reduced pressure speed. At this time, it is difficult to realize a state where the battery internal pressure is higher than the battery external pressure, and the inspection accuracy is reduced. It is more preferable that the pressure reduction rate is 1 MPa / sec or more.
[0026]
In the method of the present invention, it is effective to repeat the first step and the second step a plurality of times in order to ensure that the gas or liquid enters the battery.
[0027]
Note that the pressure in the sealed container may be reduced in advance before the battery is held under pressure in the first step. This is particularly effective when the battery is kept under a pressurized steam atmosphere in the first step.
[0028]
Further, the present invention relates to an airtightness inspection device for a sealed battery including a covered sealed container capable of housing a sealed battery, pressure adjusting means for adjusting the gas pressure in the container, and means for measuring a battery size.
[0029]
Still further, the present invention provides a hermetically sealed battery having a means for holding at least a part of the sealed battery in a pressurized liquid, a pressure adjusting means for reducing the applied pressure, and a means for measuring a battery size. It relates to an inspection device.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an airtightness inspection method for a sealed battery according to the present invention will be described.
[0031]
FIG. 1 shows an outer shape of a sealed rectangular lithium ion secondary battery 1 in which a sealing plate 3 is laser-welded to an aluminum battery case 2 as an example of a sealed battery. The sealing plate 3 is provided with a liquid injection hole, and the liquid injection hole is closed by laser welding the plug 6 after the liquid injection. The sealing plate 3 has a positive electrode terminal 4 and a safety valve 5 for explosion protection.
[0032]
For inspection of the battery, for example, an apparatus shown in FIG. 2 is used. This apparatus comprises a lid 12, a gas discharge valve 13, a gas introduction valve 14, a pressure gauge 15, a sealed container 11 having a packing 16, and a battery size measuring means 17. The battery size measuring means 17 may be provided in the sealed container 11, and the pressurizing / depressurizing unit (device A) and the size measuring unit (device B) which are separated as shown in FIG. May be combined by
[0033]
An airtightness inspection method according to the present invention is as follows. First, a plurality of batteries are prepared, arranged in a sealed container 11, and the container is sealed with a lid 12. Next, with the gas discharge valve 13 closed, the gas introduction valve 14 is opened, and air is introduced into the sealed container 11 from, for example, a high-pressure air cylinder connected to the gas introduction valve 14. When the indication of the pressure gauge 15 reaches a predetermined value, the gas introduction valve 14 is closed, and the state is maintained for a certain period of time. Thereafter, the gas discharge valve 13 is opened to discharge the air in the sealed container, and the inside of the sealed container is returned to normal pressure. Then, the battery taken out of the container is set on the battery size measuring means 17, and its size, for example, thickness is measured. Is measured.
[0034]
Usually, most of the batteries subjected to the inspection maintain their original shape, and the measured thickness is within the standard. On the other hand, some batteries are swollen, and their thickness becomes larger than the standard value. A battery whose thickness becomes larger than the standard value due to expansion is determined as a defective product having pinholes or cracks.
[0035]
Here, the case where the high-pressure air cylinder is used to increase the air pressure in the sealed container to a predetermined value has been described, but the means for increasing the air pressure is not limited to this, and even if an air compressor or the like is used. When increasing the air pressure, a means for changing the temperature of the sealed container or a means for changing the volume in the container may be used together. When depressurizing the inside of the sealed container, a decompression pump or the like may be connected after the gas discharge valve 13.
[0036]
Further, the method for inspecting the airtightness of a sealed battery according to the present invention will be described in the case where the pressurized medium is a liquid.
[0037]
For inspection of the battery, for example, an apparatus shown in FIG. 3 is used. This device comprises a lid 22, a gas discharge valve 23, a gas inlet valve 24, a pressure gauge 25, a packing 26, a sealed container 21 having a liquid inlet valve 27, a liquid outlet valve 28, and a battery size measuring means 29. In addition, the sealed container 21 and the battery size measuring means 29 may be separated as shown in FIG. 4 and both may be connected by a battery transport means, or the battery size measuring means 29 may be provided in the sealed container 21.
[0038]
The inspection process is as follows. First, with the liquid discharge valve 28 closed, the liquid introduction valve 27 is opened, for example, water is introduced into the sealed container 21, and the liquid introduction valve 27 is closed when a predetermined water depth is obtained. Subsequently, a plurality of charged lithium ion secondary batteries are prepared, and they are placed in water in the sealed container 21. At this time, the part to be inspected is submerged. After the container is sealed by the lid 22, the gas introduction valve 24 is opened with the gas discharge valve 23 closed, and air is introduced into the sealed container 21 from, for example, a high-pressure air cylinder connected to the valve 24. When the indication of the pressure gauge 25 reaches a predetermined value, the gas introduction valve 24 is closed, and the state is maintained for a certain period of time. Next, the gas exhaust valve 23 is opened to exhaust the air in the sealed container, and the inside of the sealed container is returned to normal pressure. Then, the thickness of the battery is measured by the battery size measuring means 29.
[0039]
Most of the batteries subjected to the inspection retained the original shape, and the measured thickness was within the standard. On the other hand, some batteries were swollen, and their thickness was larger than the standard value. A battery whose thickness becomes larger than the standard value due to expansion is determined as a defective product having pinholes or cracks.
[0040]
Here, a sealed container having a lid is used, and the battery is held in the pressurized water by introducing air into the container, but other means may be used for holding the battery in the pressurized water. For example, means such as colliding a high-speed water flow with the inspection site or sinking the battery deep in the water may be used.
[0041]
【Example】
Hereinafter, the present invention will be described in more detail based on examples.
[0042]
(Example 1)
As an example of a sealed prismatic lithium ion secondary battery, 100 pieces having dimensions of 34 mm in width, 50 mm in height and 5.0 mm in thickness are prepared, arranged in a sealed container 11 shown in FIG. did.
[0043]
Next, with the gas discharge valve 13 closed, the gas introduction valve 14 was opened, and air was introduced into the sealed container 11 from the air cylinder. When the indication of the pressure gauge 15 became 0.25 MPa, the gas introduction valve 14 was closed and kept in that state for 5 minutes. At this time, the ambient temperature was 25 ° C. Thereafter, the gas discharge valve 13 was opened to discharge the air in the sealed container 11, and the pressure in the container was returned to normal pressure. The pressure reduction rate at this time was about 0.2 MPa / sec. Subsequently, the lid 12 was opened, the battery was taken out, and the thickness of the battery was measured by the battery size measuring means 17.
[0044]
As a result of the measurement, 98 of the 100 batteries prepared had a thickness of approximately 5.0 mm, which was unchanged from the original dimensions. The thickness of the remaining two was 5.4 and 5.5 mm. After the inspection, these 100 batteries were subjected to a charge / discharge cycle test. About 98 pieces which did not have a dimensional change, even if charging and discharging were repeated about 100 times, no liquid leakage was observed, and there was no significant change in the discharge voltage or discharge capacity. On the other hand, for the two specimens whose thickness was increased, that is, expanded, leakage was observed from the sealing part during the charge / discharge cycle, and the discharge voltage and discharge capacity were significantly reduced with the charge / discharge cycle. did.
[0045]
From these results, it became clear that the two batteries in which expansion was observed had pinholes or minute cracks. In addition, for 98 batteries in which no dimensional change was observed, no abnormality was observed in the subsequent charge / discharge test, which revealed that there were no pinholes or minute cracks.
[0046]
(Example 2)
In the sealed container 21 shown in FIG. 3, the liquid introduction valve 27 was opened with the liquid discharge valve 28 closed, water was introduced into the sealed container 21, and when the water depth reached 10 cm, the liquid introduction valve 27 was closed. Subsequently, 100 charged lithium ion secondary batteries having dimensions of 34 mm in width, 50 mm in height, and 5.0 mm in thickness were prepared as an example of a sealed prismatic lithium ion secondary battery, arranged in a sealed container 21, and sealed with a lid 22. did. Next, with the gas discharge valve 23 closed, the gas introduction valve 24 was opened, and air was introduced into the sealed container 21 from the air cylinder. When the indication of the pressure gauge 25 became 0.25 MPa, the gas introduction valve 24 was closed and kept in that state for 5 minutes. At this time, the ambient temperature and the water temperature were set to 40 ° C.
[0047]
Thereafter, the gas exhaust valve 23 was opened to discharge the air in the sealed container 21, and the pressure in the container was returned to normal pressure. The pressure reduction rate at this time was about 0.2 MPa / sec. Subsequently, the lid 22 was opened and the battery was taken out, and its thickness was measured by the battery size measuring means 29.
[0048]
Of the 100 batteries prepared, 98 had a thickness of approximately 5.0 mm and remained unchanged from their initial dimensions. The remaining two had thicknesses of 5.9 and 6.0 mm. After completion of the inspection, 98 batteries with no dimensional change were subjected to a charge / discharge cycle test. No liquid leakage was observed even when charge and discharge were repeated about 100 times for 98 pieces having no dimensional change, and there was no significant change in discharge voltage or discharge capacity.
[0049]
For 98 batteries in which no dimensional change was observed, no abnormality was found in the subsequent charge / discharge test, which revealed that there were no pinholes or minute cracks. In addition, the charge / discharge cycle test was not performed on the two batteries in which a remarkable dimensional change was observed in the present example. However, since the remarkable dimensional change was recognized, there were pinholes or minute cracks. There is no doubt that.
[0050]
(Example 3)
As an example of a sealed rectangular nickel-metal hydride storage battery, 100 pieces with dimensions of 16.5 mm in width, 50 mm in height and 6.0 mm in thickness were prepared, and the air pressure was 0.4 MPa. Was subjected to an airtight inspection in the same manner as in Example 1.
[0051]
Of the 100 batteries prepared, 98 had no dimensional change or had a thickness of about 0.1 mm. The thickness of the remaining two was 6.2 and 6.3 mm. After the inspection, these 100 batteries were subjected to a charge / discharge cycle test. No liquid leakage was observed even when charging and discharging were repeated about 100 times for 98 pieces whose thickness did not increase, and there was no significant change in discharge voltage or discharge capacity. On the other hand, for the two specimens whose thickness was increased, liquid leakage was observed from the laser sealing part during the charge / discharge cycle, and the discharge voltage and discharge capacity were significantly reduced with the charge / discharge cycle.
[0052]
From these results, it became clear that the two batteries in which the dimensional increase was observed had pinholes or minute cracks. Further, for 98 batteries in which no dimensional increase was observed, no abnormality was observed in the subsequent charge / discharge test, which revealed that there were no pinholes or minute cracks.
[0053]
【The invention's effect】
As described above, according to the present invention, an airtight inspection of a large number of sealed batteries can be performed quickly, simply, and inexpensively.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an example of a battery which is an object of the inspection method of the present invention. FIG. 2 is a schematic cross-sectional view showing an example of an inspection apparatus used in the inspection method of the present invention. FIG. 4 is a schematic cross-sectional view showing an example of an inspection apparatus used in the method. FIG. 4 is a schematic view showing an example of an inspection apparatus used in the inspection method of the present invention.
DESCRIPTION OF SYMBOLS 1 Closed square lithium ion secondary battery 2 Aluminum battery case 3 Sealing plate 4 Positive electrode terminal 5 Safety valve 6 Sealing 11 Sealed container 12 Cover 13 Gas exhaust valve 14 Gas introduction valve 15 Pressure gauge 16 Packing 17 Battery size measuring means 21 Sealed container 22 lid 23 gas discharge valve 24 gas introduction valve 25 pressure gauge 26 packing 27 liquid introduction valve 28 liquid discharge valve 29 battery size measuring means

Claims (11)

The first step of housing the sealed battery in a sealed container and maintaining it under a pressurized gas atmosphere, the second step of reducing the gas pressure in the sealed container, and measuring the size of the battery and comparing the measured size with the standard size And a third step of judging airtightness of the sealed battery. A first step of holding at least a portion of the sealed battery in a pressurized liquid, a second step of reducing the pressure, and measuring the dimensions of the battery to determine whether the airtightness is good or not by comparing it with a standard dimension. A method for inspecting airtightness of a sealed battery, comprising the third step. 3. The method according to claim 2, wherein the liquid is water or an aqueous solution. 3. The method for inspecting airtightness of a sealed battery according to claim 1, wherein the sealed battery is held under a pressure of 0.15 MPa or more and 1.0 MPa or less in the first step. 3. The method according to claim 1, wherein the sealed battery is held under pressure for 60 seconds or more and 2 hours or less in the first step. 3. The method according to claim 1, wherein in the first step, the sealed battery is kept under pressure at a temperature of 20 ° C. or more and 60 ° C. or less. 3. The method according to claim 1, wherein the pressure is reduced at a rate of 0.1 MPa / sec or more in the second step. A first step in which a sealed battery provided with a safety valve is housed in a sealed container, and maintained in a pressurized gas atmosphere of 0.15 MPa or more and 1.0 MPa or less and lower than the operating pressure of the safety valve; A sealed battery having a second step of reducing the gas pressure in the battery at a rate of 0.1 MPa / sec or more, and a third step of measuring the dimensions of the battery and comparing the measured dimensions with the standard dimensions to determine whether airtightness is good or not. Airtight inspection method. A first step of maintaining at least a part of a sealed battery provided with a safety valve in water pressurized to a pressure of 0.15 MPa or more and 1.0 MPa or less and lower than the safety valve operating pressure at a temperature of 30 ° C. or more and 50 ° C. or less. And a second step of reducing the pressure at a rate of 0.1 MPa / sec or more, and a third step of measuring the dimensions of the battery and comparing it with the standard dimensions to determine whether the airtightness is good or bad. Airtight inspection method. An airtightness inspection device for a sealed battery, comprising: a closed sealed container capable of housing a sealed battery; pressure adjusting means for adjusting a gas pressure in the container; and means for measuring battery size. An airtightness inspection device for a sealed battery, comprising: means for holding at least a part of the sealed battery in a pressurized liquid; pressure adjusting means for increasing / decreasing pressure; and means for measuring battery size.

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