JP2007206015A - Lithium leakage detector, and lithium leakage detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly and precisely detect lithium leakage. <P>SOLUTION: The lithium leakage detector has: pulse laser irradiation means 3, 5 for plasmatizing a surface deposit substance deposited on a surface of a base material of a measuring object 8, by irradiating the surface of the measuring object convergingly with a laser beam, so as to generate fluorescence; imaging-focusing optical systems 10, 11, 12, 13, 14, 15 for collecting the fluorescence to be image-focused on fluorescence detectors; the fluorescence detectors 18a, 18b for detecting the image-focused fluorescence; and analytical means 19, 20 for detecting lithium by analyzing the detected fluorescence. A laser irradiation energy density is brought into 100 mJ/mm<SP>2</SP>or less in the pulse laser irradiation means, and the imaging-focusing optical systems image-focus 4 mm of range along a direction perpendicular to the surface of the measuring object on the fluorescence detectors. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus and method for optically detecting leakage of lithium or a lithium compound used as a battery electrolyte or the like.

  Lithium and lithium compounds are widely used as battery electrolytes, etc., but their electrical conductivity is high, and if defective products with electrolyte leakage are used, they can cause machine failure. Therefore, it is necessary to accurately detect electrolyte leakage before shipment and discriminate and eliminate defective products. However, at present, it is difficult to detect lithium with high accuracy, and visual inspection is mainly used (for example, (See Patent Documents 1 and 2). However, with increasing demand for lithium batteries, there is a demand for improved inspection speed and reliability in the production line. In order to meet this demand, it is necessary to increase the number of inspection personnel at present.

  In addition, as a technique for detecting leakage of an electrolyte in a secondary battery such as a lithium battery, a technique for detecting fluorescence generated by irradiating light or ultraviolet light that reacts with the electrolyte is known (for example, a patent) References 3, 4, and 5).

Here, there is a technique called laser-induced breakdown spectroscopy (LIBS: Laser Induced Breakdown Spectroscopy) as an on-line lithium leakage detection means. In this LIBS method, plasma is generated by irradiating a measurement sample with a laser, and elements contained in the sample are detected from the emission spectrum. This method is highly sensitive to alkali metal detection. It is known to be highly sensitive.
Japanese Patent Laid-Open No. 10-172618 JP-A-8-162126 JP 2001-297799 A JP 2002-246072 A JP 2000-310596 A

  In order to measure the leakage of minute electrolytes, it is possible to improve the sensitivity by increasing the energy density to be irradiated. However, increasing the energy density increases the damage to the base material due to ablation. There is a possibility of impairing performance. Therefore, the laser intensity to be irradiated must be minimized.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a lithium leakage detection device and a lithium leakage detection method capable of detecting lithium or a lithium compound quickly and with high accuracy. To do.

In order to achieve the above object, the lithium leakage detection apparatus according to the present invention converts the surface adhering substance adhering to the surface of the base material of the measurement object into plasma by condensing and irradiating the surface of the measurement object with pulsed laser light. Pulse laser irradiation means for generating fluorescence, an imaging optical system for collecting the fluorescence and imaging it on a fluorescence detector, a fluorescence detector for detecting the imaged fluorescence, and the detected fluorescence And an analyzing means for detecting lithium by analyzing the laser, the pulse laser irradiating means has a laser irradiation energy density of 100 mJ / mm ² or less, and the imaging optical system is connected to the surface of the object to be measured. An image of a range of 4 mm in the vertical direction is formed on the fluorescence detector.

In addition, the method for detecting lithium leakage according to the present invention generates fluorescence by converting the surface-attached substance attached to the surface of the base material of the measurement object into plasma by condensing and irradiating the surface of the measurement object with pulsed laser light. A pulse laser irradiation step, an imaging step for collecting and imaging the fluorescence, a fluorescence detection step for detecting the imaged fluorescence, and an analysis step for detecting lithium by analyzing the detected fluorescence In the pulse laser irradiation step, the laser irradiation energy density is set to 100 mJ / mm ² or less, and the imaging step forms an image in a range of 4 mm in a direction perpendicular to the surface of the measurement object. It is characterized by this.

  According to the present invention, by optimizing the measurement conditions and system, the irradiation area can be expanded, the measurement accuracy and reliability per pulse can be improved, and lithium or lithium compounds can be detected quickly and accurately. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  First, the first embodiment will be described with reference to FIGS. The lithium leak detection apparatus of this embodiment includes a laser power source 1, an oscillation timing adjuster 2, a laser oscillator 3, an optical fiber 4 for transmitting laser light to a measurement location, and an optical system 6a for shaping and irradiating the laser light on a sample. , 6b, a sample transfer device 9, a light guide 11 that transmits light emitted from plasma, wavelength selection elements 16a and 16b, fluorescence detectors (photomultiplier tubes) 18a and 18b, A signal processing determination device 20 is included.

  The sample 8 is transferred to the measurement place by the transfer device 9. The laser light oscillated from the laser oscillator 3 is guided to the upper part of the sample 8 by the optical fiber 4, and the irradiation head 5 adjusts the beam shape so as to cover the range where leakage detection is desired, and is irradiated. At this time, plasma 7 of the surface adhering substance by ablation is generated at the laser irradiation position on the sample surface. Light emitted from the plasma 7 is imaged on the light guide 11 by the lens 10.

Next, FIG. 2 is a plot of the relationship between the laser irradiation energy and the outer peripheral height, inner depth, and fluorescence intensity of the irradiation mark engraved on the sample. According to FIG. 2, by setting the laser irradiation energy to 100 mJ / mm ² or less, sufficient Li fluorescence intensity can be obtained, and the depth of the irradiation mark of the base material by the laser is within −0.34, the height Can be made within 1 μm, and can be accommodated by damage of about 1/1000 or less of the plate thickness of 0.4 mm.

In addition, FIG. 3 shows a digital image of an image obtained by irradiating a laser beam having a beam diameter of 0.7 mm and an energy density of 55 mJ / mm ² on an Al plate, and the emission intensity is changed to a color (light / dark). ) Displayed separately. The range where the peak intensity is 10% or less is a beam diameter of about +1.5 mm in the horizontal direction and a height of about 1.45 mm in the vertical direction. When the laser irradiation energy is increased, this range further expands, and this range varies depending on the type of the base material and the pressure condition, but at the atmospheric pressure level, it is about twice as large. If the fluctuation of the laser irradiation point is taken into consideration, the region to be observed is expected to be the maximum, the beam diameter +5 mm or less in the horizontal direction and 4 mm or less in the vertical direction.

FIG. 4 shows an enlarged view of the vicinity of the irradiated part. When the laser intensity is set to 100 mJ / mm ² or less and irradiated in the atmosphere, the plasma spreads about 4 mm from the surface. Therefore, the focal length of the lens 10 and the size of the light receiving surface of the light guide 11 are set so that an image with a diameter of 4 mm can be formed. It shall be decided. The light guide 11 is assumed to have a large light-receiving surface at the incident portion and smaller than the light-receiving surface of the fiber 12 at the output portion, such as a tapered bundle optical fiber. The light emitted from the light guide 11 is guided to the light measurement unit by the optical fiber 12.

  The light emitted from the optical fiber 12 is collimated by a lens 13 and then divided by a half mirror 14 and a mirror 15 and guided to photomultiplier tubes 18a and 18b. High-voltage power supplies 17a and 17b are connected to the photomultiplier tubes 18a and 18b, respectively. Interference filters 16a and 16b are installed in front of the photomultiplier tubes 18a and 18b, respectively, and one of the transmission wavelengths is 670.5 nm or 610.4 nm, which is the fluorescence wavelength of lithium, and the other transmission wavelength is the fluorescence of lithium. It is desirable to keep the wavelength 10 nm or more away. Signals from the photomultiplier tubes 18a and 18b are measured by a signal measuring device 19 with a gate function. It is desirable to set the measurement gate to an optimum setting depending on the base material.

  For example, FIG. 5 is a time waveform of aluminum with lithium attached. According to FIG. 5, it can be seen that when the base material is aluminum, the background attenuation is relatively fast, so that the base material is preferably provided between 0 and 100 μs from the laser irradiation timing. Since the background light emission is strong when the container material of the lithium battery is stainless steel, delaying the gate by 5 μs or more in order to avoid the background peak has the effect of improving the sensitivity. The determination device 20 takes in a signal from the signal measurement device 19 and determines the presence or absence of lithium according to the level. For example, as shown in FIG. 6, the lithium emission signal intensity for each sample is measured, and the sample No. in FIG. A product exceeding the threshold, such as 20, is determined as a defective product (with leakage).

  An example of a measurement procedure flow will be described with reference to FIG. First, a new sample (measurement object) is set at the laser irradiation position (step S1). Next, a laser is irradiated (step S2), and the fluorescence intensity is measured (step S3). Whether or not the measured fluorescence intensity exceeds a predetermined threshold value is determined by the determination device 20 (step S4).

  When the fluorescence intensity exceeds a predetermined threshold value, it is determined that there is lithium leakage (defective product), the defective product collecting device 21 is activated (step S5), and the sample is moved to the collection place as a defective product (step). S6). If the fluorescence intensity is below a predetermined threshold, the sample is sent to the next process (step S7). Each of the above steps is repeated with the samples replaced one after another, and continues until the last sample is processed (step S8).

  According to the present embodiment, the irradiation energy per pulse can be kept low by improving the sensitivity, and thereby a wide range can be measured at a time. Thus, as in the conventional method, a single sample is irradiated with a plurality of pulses. There is no need to detect leaks quickly and reliably.

Next, a second embodiment will be described with reference to FIGS. In this embodiment, when the laser intensity is 100 mJ / mm ² or less and irradiation is performed in the atmosphere, the plasma spreads by about 5 mm from the laser spot diameter D1, so the fluorescence condensing system (imaging optical system) is shown in FIG. In this way, by providing an angle with respect to the sample surface and collecting light from an oblique direction, it is possible to measure spatially spread fluorescence at a time. FIG. 9 shows an enlarged view of the condensing part. When the laser spot diameter is D1 and the optical axis angle of the fluorescence condensing system is θ, the lens focal length and the light guide incident aperture D2 are determined so that the following expression (1) is satisfied.

D2 ≧ (D1 + 5 mm) sin θ × f2 / f1 (1)
According to this embodiment, it becomes possible to measure all the fluorescence which spreads spatially at once, and leads to an improvement in sensitivity.

  Next, a third embodiment will be described with reference to FIGS. 10 and 11. In this embodiment, the laser light transmission optical fiber 4 is a bundle optical fiber 4a in which cores are arranged in a ring shape at the exit of the optical fiber, as shown in FIG. As shown in FIG. 11, a ring-shaped plasma 7 is generated by irradiating a ring-shaped optical fiber emission light with an appropriate size imaged on the sample. In the fluorescence condensing system, when the diameter of the ring-shaped plasma is D1 and the optical axis angle of the fluorescence condensing system is θ, the lens focal length and the light guide incident aperture D2 are determined so that the following expression (2) is established.

D2 ≧ (D1 + 5 mm) sin θ × f2 / f1 (2)
Usually, the coin-type battery is most likely to leak around the O-ring. Therefore, an improvement in sensitivity can be expected by irradiating the ring-shaped beam along the inside of the O-ring.

  According to this embodiment, it is possible to irradiate a place to be inspected at a time, and it is possible to reduce the number of irradiation pulses necessary for the inspection.

  Next, a fourth embodiment will be described with reference to FIG. In the present embodiment, a beam that has been shaped into a rectangle using the homogenizer 40 is irradiated. The laser beam 22 is expanded by magnifying lenses 23a and 23b and divided by cylindrical lens arrays 24a and 24b. The divided beams are irradiated by being superimposed on the surface of the sample 8 by the lens 25, so that the energy is uniform. The condensing optical system is designed so as to form an image in the range of the size of the side of the rectangular beam + 5 mm.

  According to the present embodiment, it is possible to uniformly irradiate a place necessary for measurement at a time when the measurement target is a square shape.

  Next, a fifth embodiment will be described with reference to FIGS. 1 and 13. As shown in FIG. 13, plasma emission is divided into two by a half mirror 14, an interference filter that passes only the fluorescence wavelength of lithium as one wavelength selection element, and an element contained in the base material as another wavelength selection element. A filter that passes only the emission wavelength is used. FIG. 13A shows the intensity of the emission wavelength component of lithium, and FIG. 13B shows the signal intensity of the wavelength component of aluminum as the base material. FIG. 13 (c) shows the lithium signal intensity divided by the aluminum signal intensity.

  In FIG. Although 20 samples exceed the threshold, there is no significant difference from the other samples when compared in FIG. That is, when the emission intensity of the plasma itself is increased, the signal intensity is apparently increased, but it does not actually reflect the amount of lithium, and causes erroneous determination. Therefore, misjudgment is prevented by using the ratio with the emission intensity of the element contained in the base material for judgment.

  According to the present embodiment, the determination accuracy can be improved.

  Next, a sixth embodiment will be described with reference to FIGS. 14 and 15. As shown in FIG. 14, the generated plasma 7 is condensed by the condenser lens 10, and the plasma is measured as an image image by the CCD camera 26. In order to select a wavelength component, an interference filter 16 that transmits only the lithium fluorescence wavelength is installed in front of the lens 10. The CCD camera 26 is a CCD camera with a gate, and the measurement accuracy can be improved by setting the measurement gate to an optimum setting depending on the base material. The image image taken by the CCD camera 26 is subjected to data processing by the image processing device 27, and the determination device 20 determines the presence or absence of lithium leakage from the result.

  An example of the determination method is shown in FIG. When the signal intensity at each location is calculated by dividing the irradiation point in the ring-shaped light emission image shown in FIG. 15A, and the signal intensity for each spot is plotted, a graph as shown in FIG. 15B is obtained. . When the leaked portion is a minute region, the signal may be buried if the signal is averaged over the entire irradiation region. Therefore, it is possible to detect minute leaks by measuring with an image and evaluating the fluorescence intensity at each location.

  Therefore, according to the present embodiment, measurement sensitivity and determination accuracy can be improved.

  Next, a seventh embodiment will be described with reference to FIG. As shown in FIG. 16, an inert gas such as a rare gas is injected from the nozzle 28 as an assist gas to the irradiation unit. When plasma is generated by irradiating a laser, the components blown off by ablation may adhere to the lens and adversely affect the measurement, but an inert gas having no emission wavelength is irradiated near the lithium emission line. By spraying on the part, it can be prevented from adhering to the lens. For example, the assist gas is helium gas, and the helium gas emitted from the helium gas cylinder 29 is injected onto the sample surface by the nozzle 28.

  Plasma emission generated by laser irradiation is divided into two by a half mirror 14, and a first filter (interference filter) that passes only the fluorescence wavelength of lithium is used as one wavelength selection element, and the other wavelength. A second filter that passes only the emission wavelength of the element contained in the helium gas is used as the selection element.

  Further, in the fifth embodiment, the plasma fluctuation is calibrated by the fluorescence intensity of the base material, but in the seventh embodiment, the plasma fluctuation can be calibrated by using the fluorescence intensity of the assist gas. The determination method is shown in FIG.

  FIG. 17A shows the intensity of the emission wavelength component of lithium, and FIG. 17B shows the signal intensity of the wavelength component of the element contained in the helium gas. FIG. 17C shows the signal intensity of lithium divided by the signal intensity of helium gas. In FIG. Although 20 samples exceed the threshold, there is no significant difference from the other samples when compared in FIG. That is, when the emission intensity of the plasma itself is increased, the signal intensity is apparently increased, but it does not actually reflect the amount of lithium, and causes erroneous determination. An erroneous determination is prevented by using the ratio of the light emission intensity of the element contained in the base material for the determination.

  According to the present embodiment, the determination accuracy can be improved.

  In the eighth embodiment, a step of washing the sample with water, ethanol or the like and removing lithium ions attached other than leakage is arranged in the step before leakage detection. A minute amount of the electrolytic solution adhering when the battery is assembled may be detected, which may cause erroneous determination. Therefore, in this embodiment, the process before washing detection is performed with water, ethanol, etc., and the process of removing the lithium ions adhering to other than the leakage is arranged, so that the lithium of the object to be leaked is highly sensitive to leakage. So that it can be detected.

  According to the present embodiment, the determination accuracy can be improved.

The typical block diagram of 1st Embodiment of the lithium leak detection apparatus which concerns on this invention. The graph which shows the relationship between a laser irradiation energy density, fluorescence intensity, and the irradiation trace of a base material. Graph showing the spatial spread of laser breakdown plasma. The typical expansion perspective view of the laser irradiation part of FIG. It is a graph which shows the time waveform of the output of the photomultiplier tube of FIG. 1, Comprising: (a) is a characteristic figure which shows the case where a base material is aluminum, (b) shows the case where a base material is stainless steel. It is a figure explaining the operation example of 1st Embodiment of the lithium leak detection apparatus which concerns on this invention, Comprising: The graph which shows the lithium fluorescence signal intensity | strength for every sample. The procedure flow figure which shows the example of an operation procedure of 1st Embodiment of the lithium leak detection apparatus which concerns on this invention. The typical block diagram of 2nd Embodiment of the lithium leak detection apparatus which concerns on this invention. The typical expansion perspective view of the laser irradiation part of FIG. The perspective view of the fiber for laser beam transmission in 3rd Embodiment of the lithium leak detection apparatus which concerns on this invention. The typical perspective view of the laser irradiation part in 3rd Embodiment of the lithium leak detection apparatus which concerns on this invention. The typical perspective view which shows the structural example of the homogenizer in 4th Embodiment of the lithium leak detection apparatus which concerns on this invention. It is a graph for demonstrating the operation example of 5th Embodiment of the lithium leak detection apparatus which concerns on this invention, Comprising: (a) is lithium fluorescence signal intensity | strength, (b) is aluminum fluorescence signal intensity | strength, (c) is lithium The graph showing the ratio of fluorescence signal intensity and aluminum fluorescence signal intensity. The typical block diagram of 6th Embodiment of the lithium leak detection apparatus which concerns on this invention. It is a figure which shows the lithium leak determination method by 6th Embodiment of the lithium leak detection apparatus based on this invention, Comprising: (a) is a perspective view which shows a ring-shaped light emission part, (b) is a lithium fluorescence signal in each irradiation point. A graph showing strength. The typical block diagram of 7th Embodiment of the lithium leak detection apparatus which concerns on this invention. It is a graph for demonstrating the operation example of 7th Embodiment of the lithium leak detection apparatus which concerns on this invention, Comprising: (a) is lithium signal strength, (b) is helium signal strength, (c) is lithium signal strength. And a graph showing the ratio of helium signal intensity.

Explanation of symbols

1: laser power source, 2: timing adjuster, 3: pulse laser oscillator (pulse laser irradiation means), 4: optical fiber (pulse laser irradiation means), 5: irradiation head (pulse laser irradiation means), 6a, 6b: condensing Lens, 7, 7a, 7b, 7c: Breakdown plasma, 8: Sample (object to be measured), 8a, 8b, 8c: O-ring, 9: Sample transfer device, 10: Fluorescent condensing lens (imaging optical system) 11: Light guide (imaging optical system), 12: optical fiber (imaging optical system), 13: lens, 14: half mirror, 15: mirror, 16a, 16b (imaging optical system): interference filter, 17a, 17b: high-voltage power source, 18a, 18b: photomultiplier tube (fluorescence detector), 19: signal measuring device (analyzing means), 20: determination device (analyzing means), 21: defective product collecting device 22: laser beam, 23a, 23b: beam expanding lens, 24a, 24b: cylindrical lens array, 25: condenser lens, 26: CCD camera, 27: image processing device, 28: nozzle, 29: helium gas cylinder

Claims (14)

A pulsed laser irradiation means for generating fluorescence by converting the surface adhering substance adhering to the surface of the base material of the measuring object into plasma by condensing and irradiating the surface of the measuring object with pulsed laser light;
An imaging optical system for collecting the fluorescence and forming an image on a fluorescence detector;
A fluorescence detector for detecting the imaged fluorescence;
Analyzing means for detecting lithium by analyzing the detected fluorescence;
Have
The pulse laser irradiation means has a laser irradiation energy density of 100 mJ / mm ² or less,
The imaging optical system forms an image of a range of 4 mm on the fluorescence detector in a direction perpendicular to the surface of the measurement object;
Lithium leak detection device characterized by   2. The lithium leak detection apparatus according to claim 1, wherein the imaging optical system forms an image of a laser condensing aperture of +5 mm on the fluorescence detector. The pulse laser irradiation means can irradiate the measurement object by shaping the laser beam into a ring shape,
The imaging optical system forms an image of a diameter of the ring +5 mm on the fluorescence detector when the laser beam is shaped into a ring shape;
The lithium leakage detection device according to claim 1, wherein:   2. The lithium leak detection apparatus according to claim 1, wherein the pulse laser irradiation means includes a homogenizer that equalizes energy density by dividing and superimposing laser beams.   5. The lithium leak detection device according to claim 4, wherein the pulse laser irradiation means has an optical system that forms an image of a range of the length of the side of the focused spot + 5 mm.   6. The lithium leakage detection apparatus according to claim 1, wherein the imaging optical system includes a wavelength selection element having a transmission wavelength of 670.5 nm.   6. The lithium leakage detection apparatus according to claim 1, wherein the imaging optical system includes a wavelength selection element having a transmission wavelength of 610.4 nm. There are at least two fluorescence detectors,
The imaging optical system splits and forms an image on each of the fluorescence detectors,
A wavelength selection element that transmits the fluorescence wavelength of lithium is arranged in the middle of the optical path imaged on one fluorescence detector, and the base material of the measurement object is located in the middle of the optical path imaged on the other fluorescence detector. A wavelength selection element that transmits the fluorescence wavelength of the element contained in
The analyzing means comprises means for determining the presence or absence of lithium leakage based on the intensity ratio of the luminescent components obtained from the at least two fluorescence detectors;
The lithium leakage detection device according to claim 1, wherein   9. The fluorescent detector according to claim 1, further comprising a CCD camera, and means for acquiring a fluorescence intensity distribution of lithium in plasma as an image image based on an output of the CCD camera. Lithium leakage detection device according to item.   The said fluorescence detector is equipped with the gate adjustment means which provides a gate width within 100 microseconds with respect to the irradiation timing of a laser, when the material of the base material of a measuring object is aluminum. 10. The lithium leakage detection device according to any one of 9 above.   The fluorescence detector includes a gate adjusting means for delaying the gate by 5 μs or more with respect to the laser irradiation timing and making the gate width within 100 μs when the base material of the measurement object is stainless steel. The lithium leakage detection device according to claim 1, wherein The lithium leakage detection device further includes a gas injection means for injecting an inert gas in the vicinity of the surface of the measurement object to be irradiated with the pulsed laser light,
The imaging optical system includes a half mirror that divides the optical path of the fluorescence into two, a first filter that is disposed in one optical path divided by the half mirror and transmits only the fluorescence wavelength of lithium, and A second filter disposed in the other optical path divided by the half mirror and allowing only the emission wavelength of the element contained in the inert gas to pass through,
The fluorescence detector includes separate fluorescence detectors for detecting fluorescence that has passed through the first filter and fluorescence that has passed through the second filter, respectively.
The lithium leakage detection device has means for determining the presence or absence of lithium leakage based on the intensity ratio of two luminescent components obtained from the fluorescence detector,
The lithium leakage detection device according to claim 1, wherein A pulsed laser irradiation step for generating fluorescence by converting the surface adhering substance attached to the surface of the base material of the measuring object by condensing and irradiating the surface of the measuring object with pulsed laser light;
An imaging step of collecting and imaging the fluorescence; and
A fluorescence detection step for detecting the imaged fluorescence;
An analyzing step of detecting lithium by analyzing the detected fluorescence;
Have
In the pulse laser irradiation step, a laser irradiation energy density is set to 100 mJ / mm ² or less,
The imaging step is to image a range of 4 mm in a direction perpendicular to the surface of the measurement object;
A method for detecting lithium leakage.   The lithium leak detection method according to claim 13, further comprising a cleaning step of removing lithium ions attached to the surface of the measurement object before the pulse laser irradiation step.

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