JP2020004646A - Secondary battery, inspection method of battery container, and manufacturing method of secondary battery - Google Patents

Abstract

To provide a secondary battery capable of increasing reliability of a weld part of a battery, an inspection method of a battery container, and a manufacturing method of the secondary battery.SOLUTION: A secondary battery 30 comprises a battery container 300 in which an opening part 310C of a case 310 housing a power generation element is sealed with a lid 320. The secondary battery 30 comprises a melting part in which a peripheral contact part 330 of the opening part 310c of the case 310 and an outer peripheral part of the lid 320 is melted in a peripheral direction by a laser welding. The melting part is a convex-shaped region having a tip end part directed to an inner side by being reduced from an outer surface of the battery container to an inner side. In the convex shape, the tip part is directed to the contact part 330 in the inner side of the battery container, and is expanded to left and right at a position where a laser beam is irradiated in a front surface part of an outer side of the battery container 300. The tip part does not reach the inner side of the battery container 300, and the front surface part reaches a side surface opposite to a flat surface which is welded with a laser in the outer side of the battery container 300 in one of the left and right of a cross section.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a secondary battery in which a lid is laser-welded to a case, a method for inspecting a battery container, and a method for manufacturing a secondary battery.

  BACKGROUND ART Conventionally, there is a secondary battery including a battery container in which a metal lid is welded to a metal case by irradiation of a laser beam. In such a secondary battery, high-precision laser welding is performed between the metal lid and the case in order to maintain high hermeticity so that the electrolyte or the like in the battery container does not leak outside. Has been done. For example, Patent Literature 1 describes an example of a technique for evaluating the penetration depth as an example of a technique for evaluating the suitability of welding.

  The evaluation method described in Patent Literature 1 is a method for evaluating a welding penetration depth of a welded portion in a battery container (work) formed by laser welding a case (can body) and a lid (lid member). . This method includes the steps of: acquiring an echo signal by scanning while transmitting an ultrasonic wave to the battery container; and imaging the echo signal corresponding to each of the lid surface and the interface between the case and the lid by using an image. And an imaging step. The method further includes a binarizing step of converting the imaged surface echo image and the interface echo image into a binarized image, and converting the binarized surface echo image from the binarized surface echo image. And a subtraction step of performing subtraction. Further, the method includes a contour extraction step of extracting a contour of the welded portion from the subtracted image, and a determination step of calculating a weld penetration depth of the welded portion based on the contour to determine the quality of the welded portion, Have.

JP 2010-14554 A

  According to the evaluation method described in Patent Document 1, it can be evaluated over the entire circumference of the battery container whether or not the welding penetration depth between the case and the lid of the battery container has not reached the inner peripheral side of the battery container. However, the reliability of the battery container is not determined only by the welding penetration depth. That is, there is room for improvement in the manufacture of a battery having a highly reliable welded portion in the battery container.

  The present invention has been made in view of such circumstances, and has as its object to improve the reliability of a welded portion of a battery, a method of inspecting a battery container, and a method of manufacturing a secondary battery. Is to provide.

  A secondary battery that solves the above problem is a secondary battery including a battery container in which an opening of a metal case housing a power generation element is sealed by a metal lid, wherein the opening of the case is provided. A peripheral contact portion with an outer peripheral portion of the lid includes a fusion portion that is melted in a circumferential direction of the contact portion by laser welding, and the fusion portion has a cross section orthogonal to the circumferential direction. The region melted by the laser welding is a convex-shaped region having a tip portion that is reduced inward from the outer surface of the battery container toward the inside and has a tip portion directed inward, and the convex shape has a cross section orthogonal to the circumferential direction. In the above, the front end portion is directed to the contact portion inside the battery container, and the outer surface portion of the battery container is spread right and left at a position where the laser beam for laser welding is irradiated. , The tip portion is the battery container. Of a not reached the inside, the surface portion, one of the right and left of the cross section reaches the side surface relative to the laser welded plane outside of the battery container.

  A method for inspecting a battery container that solves the above problem is a battery container for a secondary battery in which an opening of a metal case is sealed with a metal lid, wherein the opening of the case and the lid are provided. An inspection method for inspecting a battery container having a molten portion in which a circumferential contact portion with an outer peripheral portion of a body is melted in a circumferential direction of the contact portion by laser welding with a laser beam, In a cross section, for the cross section orthogonal to the circumferential direction, an image including a region melted by the laser welding is obtained, and based on the obtained image, a region melted by the laser welding is used for the battery container. A convex-shaped region having a front end portion that is reduced inward from the outer surface toward the inside, and has a front end portion inside the battery container in a cross section orthogonal to the circumferential direction. Facing the abutment And the outer surface of the battery container extends to the left and right of the position irradiated with the laser beam, the tip does not reach the inside of the battery container, and the surface portion is the cross section. It is inspected that one of the left and right has reached a side surface with respect to the laser-welded plane outside the battery container.

  The inventors have found that the boundary portion formed between the case and the lid of the secondary battery, the boundary portion including the boundary between the molten portion and the non-melted portion has a relatively low strength, Has a tendency to crack. In this regard, according to this configuration or method, the molten portion has a convex shape, and the tip portion is directed to the contact portion inside the battery container, and the surface portion is outside the battery container. Therefore, it spreads to either thickness in the left-right direction. Thereby, the boundary portion including the boundary line formed between the molten portion and the non-melted portion in the battery container has an arc shape that is longer than the plate thickness and longer than the straight line. Therefore, even if the boundary portion has low strength, the strength is increased by lengthening the boundary portion, and the force and time required for breaking increase, so that the reliability of the fusion zone is improved.

In a preferred configuration, the convex shape has a center line extending from the surface portion toward the tip portion within 0.3 mm of the contact portion inside the battery container.
According to such a configuration, since the center line passing through the protruding tip portion is within 0.3 mm with respect to the contact portion inside the battery container, the welded portion from the tip portion to the side portion does not melt. The length of the border between the parts can be longer.

  As a preferable configuration, when the fusion portion is a boundary portion between the non-fusion portion reaching the side surface from the tip portion of the convex shape, when the surface portion is viewed from the contact portion inside the battery container, In the viewing direction, it is arranged within a range of less than 90 degrees on the side surface side of the center line.

  As a preferable method, in the inspection, the boundary of the convex shape reaching the side surface is equal to or longer than a predetermined length, and extends from the contact portion inside the battery container to the outside of the battery container. When viewed, it is inspected whether or not it is arranged within a range of less than 90 degrees on the side surface side from the center line of the convex shape in the viewing direction.

  According to such a configuration or method, since the spread of the fusion portion is less than 90 degrees with respect to the direction in which the outside of the battery container is viewed from the contact portion inside the battery container, the fusion portion reaching the side surface from the tip portion The boundary between the metal and the non-melted part can be lengthened.

As a preferable method, an image including a region melted by the laser welding is acquired by an X-ray CT apparatus.
According to this method, with an X-ray CT apparatus, regulations on imaging conditions are relaxed, and a tomographic image can be acquired in a manner in which the time required for imaging is suppressed to the same level as in the related art. For example, restrictions on the evaluation method described in Patent Literature 1, for example, omitting or simplifying the work of disposing a battery in water in a water tank or having to bring an ultrasonic sensor close to a battery container. Can be.

As a preferred method, the predetermined length is a shortest distance from the tip of the convex shape to the side surface of the battery container.
According to such a method, the length of the boundary portion between the welded portion from the front end portion to the side surface portion and the non-fused portion becomes longer.

  A method of manufacturing a secondary battery that solves the above-described problem is a method of manufacturing a secondary battery including a battery container that is laser-welded in a manner that can change the energy intensity irradiated with laser light, and includes an image acquisition unit. An image at the irradiation position of the laser light and its surroundings is obtained, an emission image of the image is extracted by an extraction unit, and a light emission image of the image is obtained by a control unit, and a light-dark value and a melting point set in advance in a storage unit From the relationship of the depth, the energy intensity of the irradiation of the laser light is controlled so that the melting depth becomes a predetermined depth, and the correction unit sets the brightness value preset in the storage unit. And correcting the relationship between the fusion depth, wherein the correction unit compares the fusion depth of the laser beam irradiation location at the past correction timing and the emission image of the image at the past correction timing. And said Wherein correcting the relationship between the brightness value and the fusion depth is preset to 憶部.

  According to such a method, even if a change occurs in the relationship between the light and dark value and the melt depth due to the state of the material, the shape and output of the laser beam, the relationship between the light and dark value and the melt depth is corrected by comparison at the correction timing. Since the energy intensity of the laser beam irradiation is controlled by the relationship between the corrected brightness value and the melting depth, laser welding is suitably performed.

As a preferable method, the melting depth of the laser beam irradiation location is measured by a nondestructive inspection using an X-ray CT apparatus.
According to such a method, the melt depth can be measured with high accuracy by nondestructive inspection without mechanical deformation. In addition, in the case of a nondestructive inspection that does not require a cutting interval or a cutting margin, a continuous inspection can be performed in a direction in which the state of the fused portion extends. In particular, it has been newly found that an X-ray CT apparatus can clearly measure a range in which a change in density has changed due to resolidification. With an X-ray CT apparatus, it is possible to acquire a tomographic image in a form in which regulation on imaging conditions is suppressed and the time required for imaging is suppressed to the same level as in the related art.

As a preferred method, the relationship between the light-dark value and the fusion depth is determined for each welding position or welding section of the welding object.
According to such a method, even if the relationship between the brightness value and the melting depth changes depending on the welding position and the welding section of the welding target, the relationship between the brightness value and the melting depth is determined at the welding position and the like. Therefore, appropriate welding can be performed at each welding position and the like.

  As a preferred method, in the secondary battery provided with a battery container in which an opening of a metal case accommodating a power generation element is sealed by a metal lid, And a peripheral contact portion between the outer peripheral portion of the cover and the outer periphery of the lid, the determination unit, based on the light emission image of the image acquired over the entire circumference of the contact portion, the brightness value and the melting depth. It is determined whether or not the melt depth over the entire circumference is appropriate based on the fact that the melt depth over the entire circumference of the contact portion is acquired from the relationship.

  According to such a method, by continuously monitoring the light emission image of the image over the entire circumference of the contact portion in the circumferential direction, it is a defect of the contact portion of the secondary battery, and it is overlooked by cutting at predetermined intervals. Even if there is a problem that may be caused, it can be detected.

  As a preferable method, the laser beam has a first laser beam having an intensity distribution of Gaussian type and a second laser having an irradiation diameter larger than that of the first laser beam and having a top hat type intensity distribution. A laser beam generated by combining the laser beam with the laser beam, wherein the laser beam has a distribution in which the intensity of the generated laser beam has a maximum value at a central portion surrounded by a peripheral portion.

  According to such a method, the laser beam applies energy on average to the corresponding irradiation area of the top hat type to enable stable welding, and its control is easy, and the Gaussian type is applied. A reliable welding process with high energy can be made possible at the center of the corresponding irradiation range.

  ADVANTAGE OF THE INVENTION According to this invention, the reliability of the welding part of a battery can be improved.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a secondary battery, a method for inspecting a battery container, and a method for manufacturing a secondary battery. Sectional drawing which shows typically the cross-section of the laser welding part in the embodiment. The schematic diagram which shows typically the state of the welding part at the time of the welding in the laser welding apparatus in the embodiment. It is a figure which shows the welding state in the embodiment, (a) is sectional drawing which shows a favorable welding state, (b) is sectional drawing which shows an example of the conventional welding state. 4 is a graph showing a relationship between a welding shape and durability in the same embodiment. It is a figure which shows the relationship between the light emission image and penetration depth in each welding position in the same embodiment, (a) is an image which shows a light emission image, (b) is sectional drawing which shows a fusion depth. 7 is a graph showing a relationship between a light-dark value and a melting depth and correction in the embodiment. 5 is a flowchart showing a procedure for inspecting a fusion state of a fusion part in the embodiment.

One embodiment of a secondary battery, a method of inspecting a battery container, and a method of manufacturing a secondary battery will be described with reference to FIGS.
As shown in FIG. 1, a laser welding apparatus used for manufacturing a secondary battery irradiates a laser beam L2 generated based on an oscillation laser beam L0 output from a laser oscillator 110 to a welding target. I do. The laser welding apparatus includes the laser oscillator 110 that oscillates and outputs a laser beam, and a laser output unit 200 that irradiates an oscillation laser beam L0 output from the laser oscillator 110 to a welding target. Further, the laser welding device is used for a welding control unit 500 for controlling laser welding, an X-ray CT device 600 for measuring the melting depth of the battery container 300 by nondestructive inspection, and for determining the melting depth during laser welding. And a judgment data management device 700 for managing judgment data to be executed.

  The laser oscillator 110 is a so-called semiconductor laser, and oscillates a laser diode to output oscillated laser light L0. The laser oscillator 110 outputs the oscillation laser light L0 as laser light that can be used for laser welding, for example, laser light having a wavelength of 880 to 980 nanometers (nm). Further, the laser oscillator 110 outputs the intensity distribution of the energy of the oscillation laser light L0 as a predetermined type, for example, a top hat type (rectangular distribution type). Note that it is relatively easy to output a laser beam having a top hat intensity distribution from a semiconductor laser.

  The laser output unit 200 receives the oscillation laser light L0 and generates and outputs an irradiation laser light L2 for irradiating the welding target. The laser output unit 200 irradiates the output irradiation laser beam L2 to a welding target portion of the battery container 300 as a welding target.

  The battery container 300 is a secondary battery having a power generation element housed therein. The battery container 300 includes a metal case 310 and a metal lid 320 that is fitted into the opening 310c of the case 310 and seals the case 310. The case 310 and the lid 320 are An abutting portion 330 is formed. The contact part 330 is provided circumferentially between the side end part 310 a of the case 310 and the outer peripheral part 320 b of the surface 320 a of the lid 320. In the present embodiment, the surface 320a of the lid 320 forms a plane welded by laser, and the side surface 310b of the case 310 forms a side surface with respect to the plane welded by laser. The battery container 300 is continuously laser-welded with the irradiation laser light L2 emitted from the laser output unit 200 at a circumferential welding target portion set in the direction in which the contact portion 330 extends. In the present embodiment, the metal forming the case 310 and the lid 320 is aluminum or an aluminum alloy.

  The laser output unit 200 includes an intensity distribution converter 261 to which the oscillation laser light L0 is incident, a collimator lens 260 to which the output of the intensity distribution converter 261 is input, and a condenser lens 250 to emit the irradiation laser light L2. Prepare.

  The intensity distribution converter 261 outputs the incident oscillation laser light L0 as converted laser light L3 having an intensity distribution suitable for laser welding. The intensity distribution converter 261 converts the top hat oscillation laser light L0 into a converted laser light L3 having an appropriate energy intensity distribution (for example, see the energy intensity distribution D6 in FIG. 2). The intensity distribution converter 261 is a known converter and includes an optical lens, an optical fiber such as a process fiber or a double core fiber, and can change the intensity distribution of the input laser light to a target intensity distribution.

The collimator lens 260 is a lens that converts the incident converted laser light L3 into parallel light L1 and outputs the parallel light L1 to the condenser lens 250.
The condensing lens 250 emits the input parallel light L1 as irradiation laser light L2 that condenses the irradiation spot. The condenser lens 250 increases the energy intensity at the irradiation location of the irradiation laser light L2 by narrowing the irradiation diameter (for example, the diameter L2D in FIG. 2) from the outer diameter of the parallel light L1. Thereby, the irradiation laser beam L2 causes the two metal members to be welded to be melted by laser welding the two metal members.

  As shown in FIG. 2, the laser beam showing an example of the irradiation laser beam L2 has an irradiation diameter of L2D, and the energy intensity distribution D6 is surrounded by the top hat type intensity distribution D2 as a peripheral portion. This is a distribution having a Gaussian intensity distribution D1 at the center. Irradiation laser light L2 is applied to a welding target portion including contact portion 330 such that contact portion 330 between case 310 and lid 320 is included in the irradiation diameter. Then, by applying high energy to the welding target location, the contact portion 330 included in the laser irradiation location is laser-welded. Note that, as long as a long boundary line can be provided between the melting portion and the non-melting portion, the energy intensity distribution of the irradiation laser light L2 is not limited to the energy intensity distribution D6 shown in FIG. A hat-type intensity distribution, a Gaussian-type intensity distribution, or another intensity distribution may be used.

  As shown in FIG. 3, the irradiation laser light L <b> 2 is relatively moved in the direction in which the contact portion 330 extends, so that the case 310 and the lid 320 are laser-welded. At the irradiation location of the irradiation laser beam L2, the aluminum alloy is melted by the applied high energy, and a molten pool 350 made of the melted aluminum alloy is formed. On the other hand, the molten pool 350 solidifies in response to a decrease in temperature due to departure from the irradiation position of the irradiation laser beam L2, and forms a welded portion 340 that is a welded portion.

  The density of an aluminum alloy differs between before and after melting due to solidification shrinkage that occurs after melting. The present inventors have found that a difference in density generated in the battery container 300 by laser welding can be obtained as a tomographic image by the X-ray CT apparatus 600 as a difference in X-ray transmission amount.

  FIG. 4A is a cross-sectional image of the fusion part 340 formed in the contact part 330 that has been laser-welded with the irradiation laser light L2 of the present embodiment, which is orthogonal to the direction in which the contact part 330 extends (circumferential direction). is there. The irradiation laser beam L2 of the present embodiment has an energy intensity distribution (for example, the energy intensity distribution D6 in FIG. 2) adjusted so that the fusion zone 340 has the cross-sectional image shown in FIG.

  As shown in FIG. 4A, in a cross section orthogonal to the circumferential direction, the melting portion 340 has a region that is melted by laser welding reduced from the outside to the inside of the battery case 300 and the battery case 300. Has a convex-shaped region having a tip portion 341 facing the inside. The surface 320a of the lid 320 and the side end 310a of the case 310 (see FIG. 2) constitute the outer surface of the battery container 300.

  The distal end portion 341 faces the remaining portion 331 of the contact portion 330 that is located inside the battery container 300 and remains without being melted. The tip 341 has not yet reached the inside of the battery container 300 in order to avoid the possibility that molten metal or the like may enter the inside.

  In the region of the convex shape, in a cross section orthogonal to the circumferential direction, the surface portion 342 of the fusion portion 340 extends right and left with respect to the irradiation position LP of the irradiation laser beam L2. In the cross section of the fusion zone 340, the surface portion 342 outside the battery case 300 is mostly the flat surface of the battery case 300 including the contact portion 330 (the surface 320 a of the lid 320 and the side end portion 310 a of the case 310). ), A part of the right side has reached the side surface 310 b of the case 310, which is the side surface with respect to the plane of the battery container 300.

  The convex region has a boundary portion including a boundary line L10 between the fused portion 340 and the non-fused portion in a cross section orthogonal to the circumferential direction. The boundary line L10 is formed by setting the remaining portion 331 of the abutting portion 330 as a branch point L1c, a boundary line L1b from the branch point L1c toward the lid 320 (left side in the figure), and the case 310 side of the branch point L1c (right side in the figure). Has a boundary line L1a. More specifically, the melting portion 340 is formed by a portion of the lid 320 and the case 310 that is melted by laser welding. The non-melted portion is a portion of the lid 320 and the case 310 that has not been melted by laser welding. Therefore, the boundary line L1b is on the left side of the contact portion 330 and is a boundary line formed between the fusion portion 340 and the non-fusion portion of the lid 320. The boundary line L1a is It is a boundary line formed on the right side between the melting portion 340 and the non-melting portion of the case 310. The convex region is deepest at the center corresponding to the irradiation position LP in the horizontal direction of the cross section, and becomes shallower as the distance from the center to the left and right increases. Therefore, the boundary line L10 is a curve corresponding to the shape of the convex region, and is configured as a convex curve that goes from the outside to the inside of the battery container 300.

  The melting portion 340 has a cross-section having a full width W11 as a width in the left-right direction orthogonal to the irradiation direction of the irradiation laser beam L2, a lid side width W13 on the lid body 320 side of the full width W11, and a case 310 side. It has a case-side width W. The boundary line L10 has a convex shape and is longer than the entire width W11. More specifically, since the boundary line L1b is a curve extending from the branch point L1c having a depth due to melting to the surface 320a of the lid 320, its length is ensured to be longer than the lid-side width W13. Further, since the boundary line L1a is a curve extending from the branch point L1c having a depth due to melting to the side surface 310b of the case 310, its length is longer than the case side width W which is the shortest distance from the branch point L1c. Is also secured for a long time.

  The protruding tip portion 341 is formed on an extension of the optical axis LC (center line) of the irradiation laser beam L2. In other words, in the present embodiment, the optical axis LC of the irradiation laser beam L2 is arranged within a predetermined range LD with respect to the contact portion 330 during laser welding. The predetermined range LD is a range that is smaller than the case-side width W. For example, the predetermined range LD can be set to a range of 0.3 mm, and more preferably, set to a range of 0.2 mm.

  From this, the angle α between the straight line LR connecting the branch point L1c and the position where the boundary line L1a appears on the side surface 310b of the case 310, and the straight line LH orthogonal to the optical axis LC (center line) of the irradiation laser light L2. Is greater than 0 degrees, in other words, the angle between the optical axis LC and the straight line LR is less than 90 degrees.

  Incidentally, FIG. 4B shows an example of the fusion portion 340B formed on the contact portion 330 by laser welding, which was conventionally performed without intending that the fusion portion 340 has the cross-sectional image shown in FIG. 4A. FIG.

  As shown in FIG. 4 (b), for example, in laser welding using laser light having an average energy intensity in the irradiation range, the depth of the melted portion is also average, and therefore, the melting has a shallow melting depth as a whole. A part 340B is formed. The boundary line L20 formed between the melted portion 340 and the non-melted portion has a shape closer to a straight line than the above-described boundary line L10 because the depth is generally small and the energy is average. Become. The melting portion 340B has a cross-section having a full width W21 as a width in the left-right direction orthogonal to the irradiation direction of the irradiation laser beam, a lid-side width W23 on the lid 320 side of the full width W21, and a case on the case 310 side. It has a side width W22. The boundary line L20 has a length close to the full width W21 because it is linear. Since the boundary line L2b reaches the surface 320a of the lid body 320 from the shallow branch point L2c, the boundary line L2b is secured to be slightly longer than the lid-side width W23. Further, since the boundary line L2a reaches the side surface 310b of the case 310 from the shallow branch point L2c, the length is substantially the same as the case-side width W22.

  As shown in FIG. 1, the laser output unit 200 inputs the light E <b> 1 which is the light to be irradiated to the irradiation position of the irradiation laser light L <b> 2 and the periphery thereof from the condensing lens 250, and outputs the parallel light by the spectroscope 400. It is output separately from L1. That is, the laser output unit 200 causes the light E1 to be input to the condenser lens 250 from a direction opposite to the traveling direction of the irradiation laser light L2. The light E1 includes light emitted from the welding target according to the temperature state and the melting state of the welding target portion including the molten pool 350. The spectroscope 400 transmits the parallel light L1 in the traveling direction of the parallel light L1 and transmits the light E1 incident from the opposite direction to the traveling direction of the parallel light L1 at a predetermined angle of 90 ° with respect to the reverse direction. Reflect in the direction.

The light E <b> 1 output from the laser output unit 200 at a direction 90 ° with respect to the reverse direction is input to the imaging unit 440.
The imaging unit 440 includes at least one of the visible light wavelength region and the invisible light wavelength region in the imageable wavelength region, and captures an image of light in the imageable wavelength region. That is, the molten pool 350 and its surroundings are imaged as an image composed of visible light and invisible light. The imaging unit 440 can capture, for example, light emission (wavelength: 400 to 500 nm) when the molten metal is vaporized (plasmaized) and light emission of the metal generated by melting (wavelength: 700 to 800 nm).

  The welding control unit 500 is connected to the imaging unit 440 and inputs a captured image. The welding control unit 500 includes an image acquisition unit 510 that acquires a captured image, a luminescence image extraction unit 520 that extracts a luminescence image related to a fusion state from the captured image, and a fusion depth determination unit 530 that determines a fusion depth. Is provided. In addition, the welding control unit 500 includes a storage unit 540 that stores data necessary for determining the fusion depth. The welding control unit 500 performs a welding process of joining the cover 320 to the case 310 by continuously laser welding the circumferential contact portion 330 of the battery container 300.

  The storage unit 540 is a non-volatile storage unit such as a hard disk or a flash memory, and stores determination data 541 used for determining the fusion depth and luminescence image data 542 including a light-dark value of the luminescence image. I have.

In addition, welding control section 500 outputs the determined melting depth to a display device or the like. Then, the determined melting depth is output via a display device or the like.
The image acquisition unit 510 acquires a captured image from the imaging unit 440.

  The light emission image extraction unit 520 extracts a light emission image (for example, see the light emission image 350A in FIG. 6) from the captured image from the imaging unit 440. The light emission image is an image showing a range in which light is emitted in response to melting of a welding target by laser welding. In the present embodiment, the state where the temperature of the aluminum alloy rises due to the energy from the laser beam at the laser irradiation location and its surroundings, and is melted or evaporated, is imaged. When the aluminum alloy is irradiated with the laser, energy is diffused around the laser-irradiated portion. Therefore, the range where the applied energy intensity is the same tends to be a circular shape around the laser-irradiated portion. Therefore, the molten pool 350 is also formed in a substantially circular shape, and light emission generated by melting the metal is also obtained in a circular shape.

  The fusion depth determination section 530 determines the fusion depth of the laser welded fusion section 340 based on the luminescence image extracted by the luminescence image extraction section 520 and the determination data 541. The determination data 541 is data indicating a correlation between the light-dark value of the light-emitting image and the melting depth, and can specify the melting depth corresponding to the light-dark value of the light-emitting image.

  Further, the fusion depth determination unit 530 determines the fusion depth based on the emission image data 542 and the determination data 541 stored in the storage unit 540. The fusion depth determination unit 530 obtains the brightness value of the welding position of the contact part 330 from the emission image data 542 and applies the obtained brightness value to the determination data 541 to calculate the fusion depth of the welding position. . Then, it is determined whether or not the calculated melting depth is within an appropriate range of the melting depth.

  As shown in FIG. 7, the determination data 541 is data indicating a correlation between a light-dark value and a melting depth, for example, data indicating a correlation such as a graph L71. The data indicating the correlation may be data such as list data, map data, a function or an arithmetic expression. Normally, the data indicating the correlation has a tendency that the brighter the light-dark value is, the deeper the melting depth becomes. Note that the relationship between the light and dark values and the melting depth slightly changes depending on the material thickness, the type of the material, the intensity distribution of the laser light, the irradiation diameter of the laser light, and the like. Therefore, in the present embodiment, the data indicating the correlation between the light-dark value and the melting depth can be updated at any time.

  As shown in FIG. 1, the X-ray CT apparatus 600 includes an imaging unit 610 that captures an X-ray CT image, an imaging control unit 620 that performs overall control of the X-ray CT apparatus 600, and a CT that is captured by the imaging unit 610. A storage unit 630 that stores an image. The X-ray CT apparatus 600 is a well-known X-ray CT apparatus, and captures a CT image that is a tomographic image of the fusion part 340 of the battery container 300. The X-ray CT apparatus 600 mounts a battery container 300 in which a lid 320 is laser-welded to a case 310 to be imaged on a sample stage 611 of an imaging unit 610, and photographs a CT image of the mounted battery container 300. I do. In the present embodiment, the X-ray CT apparatus 600 captures a CT image based on the “1a-1a” section line and a CT image based on the “1b-1b” section line set in a range including the fusion zone 340. For example, FIG. 4A is a CT image based on the “1a-1a” section line, and FIG. 6B is a CT image based on the “1b-1b” section line. The CT image is a CT image of the fusion part 340 in a direction (“1a-1a” cutting line) orthogonal to the direction in which the fusion part 340 is continuously formed, and is predetermined in a direction in which the fusion part 340 is continuously formed. Is a CT image continuously captured at a slice pitch of. The slice thickness and the slice pitch are set so that a clearer CT image of the fusion zone 340 can be obtained.

The imaging control unit 620 captures a CT image over the entire circumference of the fusion unit 340, and stores the CT image captured in a mode in which the imaging position in the circumferential direction can be specified in the storage unit 630.
By the way, the time required for the X-ray CT apparatus 600 to photograph the entire circumference of the fusion zone 340 is longer than the time required for laser welding the entire circumference of the fusion zone 340. Therefore, the number of batteries 30 in which X-ray CT apparatus 600 can capture the entire circumference CT image of fusion zone 340 during a certain period of time is smaller than the number of batteries 30 in which the entire circumference of contact portion 330 is laser-welded. Therefore, only the sampled battery 30 among the plurality of laser-welded batteries 30 is taken by the X-ray CT apparatus 600 for the CT image of the fusion zone 340. For example, the X-ray CT apparatus 600 captures a CT image of the latest laser-welded battery 30 at the timing when the next CT image can be captured. Then, the determination data 541 is corrected based on the CT image of the battery 30 from which the CT image was captured and the light emission image. The timing at which the laser welding of the battery 30 at which the CT image is to be taken is performed is the correction timing.

  Therefore, in the present embodiment, the X-ray CT apparatus 600 sets the timing at which the battery 30 from which the CT image was captured is laser-welded as the past correction timing, and the CT image of the battery 30 laser-welded at the same correction timing is the past. 3 is a CT image at the correction timing.

  As illustrated in FIG. 1, the determination data management device 700 manages updating of the determination data 541 used by the welding control unit 500 to determine the fusion depth based on the X-ray CT image captured by the X-ray CT device 600. . The determination data management device 700 can acquire the CT image data stored in the storage unit 630 of the X-ray CT device 600. In addition, the determination data management device 700 can acquire and update the determination data 541 stored in the storage unit 540 of the welding control unit 500, and can acquire the emission image data 542.

The determination data management device 700 includes a determination control unit 710 that performs arithmetic processing and the like, and a storage unit 720 that stores data and the like used for the arithmetic processing.
The storage unit 720 stores emission image data 721, CT image data 722, and reference data 723.

  The luminescence image data 721 is data of a luminescence image corresponding to the correction timing, and is data obtained from the luminescence image data 542 of the welding control unit 500 as corresponding to the correction timing.

  The CT image data 722 is CT image data corresponding to the correction timing, and is acquired by the determination data management device 700 from the X-ray CT device 600 each time the X-ray CT device 600 completes capturing a CT image of the battery container 300. Data.

  The reference data 723 is model data of a CT image, model data of an emission image, model data of determination data, past data of determination data, and the like. Model data of a CT image can be used as an initial value when CT image data is not acquired. In addition, the model data of the light emission image is data that can be used as an initial value of the light emission image.

The determination control unit 710 includes a CT determination unit 711 that determines a CT image, and a determination data update unit 712 as a correction unit that updates the determination data.
The CT determination unit 711 acquires the welding positions 635A to 635D (see FIG. 6B) and the fusion depth Dx (see FIG. 6B) from the CT image data 722. The welding depth 635A is the welding depth Da, the welding position 635B is the welding depth Db, the welding position 635C is the welding depth Dc, and the welding position 635D is the welding depth Dd. It is.

  Further, the CT determination unit 711 determines whether the acquired fusion depth Dx is in the NG area (see FIG. 7) or the OK area (see FIG. 7), and determines the welding position that is an appropriate depth. To identify. The NG region shown in FIG. 7 is a region where the melting depth is too shallow and insufficient melting, or a region where the melting depth is too deep and excessive melting. The OK region also shown in FIG. 7 is a region showing an appropriate melting depth.

Further, the CT determination unit 711 performs a fusion shape determination process of determining whether or not the boundary L1a of the fusion unit 340 (see FIG. 4A) is long and has high reliability.
With reference to FIG. 8, the molten shape determination processing will be described. The fusion shape determination processing is performed by the CT determination unit 711 of the determination data management device 700 based on the X-ray CT image in the CT determination unit 711.

  When the melting state determination process is started, the CT determination unit 711 acquires the angle α (see FIG. 4A) of the boundary L1a of the fusion unit 340 (Step S10 in FIG. 8). Then, the CT determination unit 711 determines whether the obtained angle α is larger than 0 degrees (Step S11 in FIG. 8). Since the distance from the tip portion 341 to the outer surface of the battery container 300 is shorter on the case 310 side of the fusion portion 340 and cracks are likely to occur, the case 310 side (right side) is particularly determined.

  When it is determined that the angle α is 0 degrees (NO in step S11 in FIG. 8), the CT determination unit 711 determines that the melted shape is inappropriate and makes an NG determination (step S17 in FIG. 8). The melting state determination processing ends.

  On the other hand, when it is determined that the angle α is greater than 0 degrees (YES in step S11 of FIG. 8), the CT determination unit 711 acquires the case-side width W of the fusion part 340 on the right side of the contact part 330 (FIG. 8 step S12). Then, the CT determination unit 711 determines whether the case-side width W is equal to or greater than the plate thickness t of the case 310 (Step S13 in FIG. 8). When it is determined that the case-side width W is less than the plate thickness t of the case 310 (NO in step S13 in FIG. 8), the CT determination unit 711 determines that the melted shape is inappropriate and makes an NG determination (FIG. 8). Step S17), the melting state determination process ends.

  On the other hand, when it is determined that the case-side width W is equal to or greater than the plate thickness t of the case 310 (YES in step S13 in FIG. 8), the CT determination unit 711 determines the boundary line of the fusion part 340 on the right side of the contact part 330 The length D10 of L1a and the thickness D11 from the tip 341 of the convex part of the fusion part 340 to the surface 320a of the lid 320 are acquired (Step S14 in FIG. 8). Then, the CT determination unit 711 determines whether the length D10 is a value larger than the thickness D11 (Step S15 in FIG. 8). When it is determined that the length D10 is equal to or less than the thickness D11 (NO in step S15 in FIG. 8), the CT determination unit 711 performs an NG determination that the melted shape is inappropriate (step S1 in FIG. 8). S17), the melting state determination processing ends.

  On the other hand, when it is determined that the length D10 is greater than the thickness D11 (YES in step S15 in FIG. 8), the CT determination unit 711 makes an OK determination that the melted shape is appropriate (FIG. 8). Step S16), the state determination processing ends.

  As illustrated in FIG. 1, the determination data update unit 712 acquires the light-dark value of the emission image data 721 and acquires the welding position of the appropriate fusion depth Dx specified by the CT determination unit 711. Then, the determination data updating unit 712 identifies the brightness value corresponding to the appropriate melting depth, identifies the graph L71 (see FIG. 7) of the “melting depth-brightness value relationship curve”, and updates the determination data. Perform update processing.

(Melting depth-brightness / darkness relationship curve)
6A and 6B, the relationship between the fusion depth Dx obtained from the X-ray CT image and the brightness value of the emission images 350A to 350D is obtained for each of the welding positions 635A to 635D. FIGS. 6A and 6B show that the darker the color, the brighter the color. For example, the melting depth Da corresponding to the luminescent image 350A, the melting depth Db corresponding to the luminescent image 350B, the melting depth Dc corresponding to the luminescent image 350C, and the luminescent image 350D. The obtained melting depth Dd is obtained as a correlation. At this time, the light-dark value of the light-emitting image is “light-emitting image 350A <light-emitting image 350B <light-emitting image 350C <light-emitting image 350D” and the melting depth is “melting depth Da <melting depth Db <melting depth Dc. <Melting depth Dd ”. Then, from this relationship, a brightness value corresponding to an appropriate melting depth can be obtained. For example, if the melting depth Dc is an appropriate melting depth, the brightness value at that time is obtained from the emission image 350C. At the same time, a light-dark value at a melt depth Da shallower than the melt depth Dc is obtained from the emission image 350A, and a light-dark value at a melt depth Dd deeper than the melt depth Dc is obtained from the light-emitting image 350D. .

  As shown in FIG. 7, an appropriate melting depth Dx is set as the median value Dm, and the melting depth is considered to be distributed between + 4σ and −4σ with respect to the median value Dm. Note that + 4σ is a value equal to or less than a standard upper limit value DH which is an upper limit at which reliability is maintained, and −4σ is a value equal to or more than a standard lower limit value DL which is a lower limit value at which reliability is maintained. And Further, a light-dark value corresponding to + 4σ is calculated from the relationship between the light-emitting image 350C and the light-emitting image 350D, and a light-dark value corresponding to -4σ is calculated from the relationship between the light-emitting image 350C and the light-emitting image 350A. In this way, a graph L71 of a "melting depth-light / dark value relationship curve" showing the correlation between the melting depth and the light / dark value is obtained. Further, from the graph L71, a light-dark value corresponding to the standard lower limit value DL of the melt depth and a light-dark value corresponding to the standard upper limit value DH of the melt depth are obtained, and an NG area for the light-dark value is determined. Is determined. According to FIG. 7, in laser welding of the entire circumference of the contact portion 330, it is preferable that the acquired light-dark value be a target normal distribution L72 centered on the target value of the light-dark value corresponding to the median value Dm. Then, when the normal distribution is biased toward dark or bright, it is preferable that those normal distributions approach the target normal distribution L72.

(Welding process)
That is, as shown in FIG. 1, the welding control unit 500 determines the amount of energy applied to the abutment unit 330 so that laser welding with an appropriate melting depth Dx can be performed, by changing the amount of energy of the light emission image of the molten pool 350. Feedback control is performed based on the value. For example, the welding control unit 500 is configured so that the output of the laser oscillator 110 can be adjusted. The welding control unit 500 performs feedback control on the intensity of the laser light output from the laser oscillator 110 whose output can be adjusted based on the brightness value of the emission image.

  When the lightness / darkness value changes to be brighter than the target value at which an appropriate fusion depth Dx is considered to be obtained (the fusion depth Dx is considered to be deeper), the welding control unit 500 assigns the energy to be applied to the welding target portion. In order to reduce the output, the output of the laser oscillator 110 is adjusted so as to decrease, so that the brightness value is controlled so as to approach the target value. Conversely, when the brightness value changes darker than the target value (the melting depth Dx is considered to be shallower), the welding controller 500 increases the output of the laser oscillator 110 in order to increase the energy applied to the welding target portion. Is controlled so that the brightness value approaches the target value.

  That is, the welding control unit 500 controls the energy intensity at which the laser beam is irradiated so that the brightness value of the dynamically changing laser irradiation position approaches the target value, so that the laser welding point has an appropriate melting depth Dx. It is to be.

  That is, referring to FIG. 6, in the laser welding, if the brightness value is bright, for example, as in light emission image 350D, the material is welded at a deep melting depth Dx as shown in welding position 635D. However, since the thickness of the case 310 and the lid 320 of the battery container 300 is thin, if the melting depth Dx becomes deeper than the standard upper limit value DH, a through hole may be generated. In addition, it is not preferable that the melting range is widened and the spatters caused by welding increase. On the other hand, if the brightness value is dark as in the light emission images 350A and 350B, the material is welded at a shallow fusion depth Dx as shown in welding positions 635A and 635B. However, there is a possibility that appropriate strength and stability for welding the case 310 and the lid 320 are not secured. Therefore, in the present embodiment, the light-dark value of the emission image extracted from the light E1 that is the observed light is given to the contact portion 330 such that the light-dark value is expected to have an appropriate melting depth. The energy intensity is adjusted.

  Further, as shown in FIG. 1, the brightness value of the entire circumference is stored as a part of the emission image data 542 based on the emission image of the entire circumference of the contact portion 330. Thereby, it is also possible to confirm afterwards whether or not the case 310 and the lid 320 are welded at an appropriate melting depth.

(Melting depth judgment processing)
As shown in FIG. 1, the welding control unit 500 controls the irradiation energy of the irradiation laser beam L2 so that the emission image of the weld pool 350 (see FIG. 3) falls within the allowable range of the determination data 541, that is, the OK region of the light and dark values. Laser welding is performed while adjusting. Incidentally, the time required to acquire an X-ray CT image with the X-ray CT apparatus 600 for one battery 30 is longer than the time required for laser welding. On the other hand, in the case of laser welding of the same member and the same shape of the battery case 300, the graph L71 (see FIG. 7) of the “melting depth-brightness / darkness relationship curve” does not change significantly.

  Therefore, the welding control unit 500 performs laser welding by continuing to use the set determination data 541 until it is updated. Accordingly, it is expected that the light and dark values of the light emission image are distributed like the target normal distribution L72 (see FIG. 7). In addition, whether or not the entire circumference of the contact portion 330 is appropriately welded is determined based on the light emission image and the graph L71 (see FIG. 7) of the “melting depth-brightness / darkness relationship curve”. If it is determined that the entire circumference has been properly welded, the battery 30 is determined to be non-defective, and if it is determined that the entire circumference has not been properly welded, the battery 30 is determined to be a re-inspected product or a defective product. If the luminescent image is in the dark NG area, it is determined that the melt depth (melt) is insufficient, and if the luminescent image is in the bright NG area, it is determined that the melt depth (melt) is excessive.

  Conventionally, when an NG product is simply found by the sampling inspection, all the batteries 30 manufactured until the previous sampling inspection need to be re-inspected or discarded. On the other hand, according to the present embodiment, it is possible to reduce the number of batteries 30 that need to be re-tested or the number of batteries 30 that need to be discarded.

  For example, as an example of narrowing down, when an NG product is found in an X-ray CT image, an emission image of this NG product and an emission image of a product that has been laser-welded since the manufacture of the product for which the previous X-ray CT image was obtained are compared. By comparison, it is possible to extract a product having a luminescence image that matches the mode of the luminescence image. The emission image in which the aspect of the emission image matches the one in which the distribution of light and dark in the entire circumference is the same, or the emission image that matches the emission image of the part causing the inconvenience in any part of the entire circumference Identified based on what they have. According to this, only the extracted battery 30 can be set as a target for re-testing, discarding, or the like.

  For example, as another example of narrowing down, the determination data management device 700 includes a graph L71 of the “melting depth-brightness / darkness value relationship curve” before updating, and a graph L71 of the “fusion depth-brightness / darkness value relationship curve” calculated this time. Are compared to determine whether the two relationship curves match. If the two relationship curves match, all the NG products after the previous X-ray CT image capturing are specified in the above example. On the other hand, when the two relationship curves do not match, the light emission image of the battery 30 manufactured after the previous X-ray CT image was captured is inspected again with the currently calculated “melting depth-brightness / darkness relationship curve” graph L71. . In this re-inspection, products corresponding to NG products are extracted, and the extracted products are re-inspected. On the other hand, the battery 30 that is determined to be non-defective in both the previous inspection using the graph L71 and the current inspection using the graph L71 is determined to be non-defective, so that re-inspection or the like may not be performed. That is, the products to be re-inspected are limited to products having the same luminescent image as NG products and products determined to be NG products in the graph L71 of the “melting depth-brightness / darkness relationship curve” calculated this time. Therefore, the labor required for re-inspection and the like can be reduced.

(Judgment data update processing)
Next, an operation of updating the determination data 541 will be described with reference to FIG.
The light emission image data 542 at the time when the battery 30 to be photographed for the X-ray CT image is laser-welded (correction timing) is specified. Further, the position in the circumferential direction of the X-ray CT image is synchronized with the position in the circumferential direction of the emission image. Then, the appropriate melting depth Dx is set as the median value Dm, and the brightness value at the welding position corresponding to the median value Dm is specified. In addition, the median value Dm, the standard lower limit value DL, and the standard upper limit value DH, which are appropriate melting depths, are defined according to the structure, type, and the like of the battery container 300. As an example, the standard lower limit value DL is 0.16 mm, and the slice interval in the circumferential direction is a minimum of 5 μm.

  First, the X-ray CT apparatus 600 measures the melting depth Dx at each welding position in the circumferential direction of the battery 30 to be inspected from the X-ray CT image, and confirms that the entire circumference is equal to or more than the standard lower limit DL. . Also, it is confirmed that the median value Dm and the variation (δ) of the melting depth Dx in the entire circumference are appropriate. As a result, the battery 30 to be inspected is first determined to be OK in the sampling inspection. Such a determination result may be output as a state display signal or a display signal.

  The determination data management device 700 obtains a brightness value corresponding to a fusion depth Dx of −4σ with respect to the median value Dm, and a fusion depth of + 4σ acquired from the X-ray CT image for which the sampling inspection is determined to be OK. And a light-dark value corresponding to Dx. Then, a “melting depth-brightness / darkness relationship curve” graph L71 is generated by combining the lightness / darkness values corresponding to the specification upper limit value DH and the specification lower limit value DL, and is used as the determination data 541. Then, the determination data management device 700 updates the determination data 541 of the welding control unit 500 with the generated determination data 541.

  The range from −4σ to + 4σ with respect to the median value Dm is assumed to be between the standard lower limit value DL and the standard upper limit value DH. Therefore, when it deviates, it is determined that the fusion depth Dx obtained in the X-ray CT image is data that is not appropriate for updating the determination data 541. As described above, the determination data management device 700 does not update the determination data 541 of the welding control unit 500 when the appropriate graph L71 of “melting depth-brightness / darkness relationship curve” cannot be generated. Alternatively, the determination data management device 700 updates the determination data 541 of the welding control unit 500 with the determination data 541 set in the reference data 723 or the previously generated determination data 541.

The effect of the present embodiment will be described.
Conventionally, when a crack generated between the lid body 320 and the case 310 and which can be confirmed from the outside is confirmed, it is possible to specify how the crack has occurred in the welded portion. could not. Also, it is difficult to confirm a crack in the middle of growing inside the battery 30 from the outside. In this regard, the inventors of the present application specify the location of the crack by taking an X-ray CT image of the fused portion 340 of the battery container 300 of the battery 30, and observe the crack over time to observe the crack. By investigating the relationship between the growth process of the battery and the fusion zone 340, it was found that the crack of the battery 30 was formed and grown along the boundary line L1a (see FIG. 4A). Further, regardless of whether the crack is in the long boundary line L1a (see FIG. 4A) or the short boundary line L2a (see FIG. 4B), the cracks in the battery 30 are all along the boundary line. Found to grow. If the crack growth rate is constant, the battery 30 having the long boundary line L1a has a high probability of lasting longer than the battery 30 having the short boundary line L2a, and the reliability of the battery 30 is enhanced.

  For example, FIG. 5 shows the relationship between the stress amplitude and the number of times of endurance for each difference in the length of the boundary line. The graph of the fusion shape L51 is a graph showing the case of the battery 30 having the boundary line L10 including the long boundary line L1a formed on the fusion zone 340 of the present embodiment. On the other hand, the graph of the fusion shape L52 is a graph of the battery 30 having the boundary L20 including the short boundary L2a formed in the conventional fusion part 340B. For example, when the stress amplitude is 10 MPa, the number of cycles of the battery 30 having the molten shape L52 including the short boundary line L2a is about 20,000, while the number of cycles of the battery 30 having the molten shape L51 is about 1,000,000. That is, in the case of the molten shape L51, the number of cycles is increased, for example, about 50 times as compared with the case of the molten shape L52, and the durability is improved, so that the reliability of the battery 30 is improved. Further, for example, if one million cycles are to be secured, the stress amplitude needs to be limited to about 10 MPa in the molten shape L51, while the stress amplitude needs to be limited to about 3.5 MPa in the molten shape L52. . That is, in the case of the molten shape L51, the stress amplitude can be increased and the durability is improved as compared with the case of the molten shape L52, so that the reliability is improved.

As described above, according to the secondary battery, the method for inspecting the battery container, and the method for manufacturing the secondary battery of the present embodiment, the following effects can be obtained.
(1) The melting portion 340 has a convex shape, and a tip portion 341 faces a contact portion 330 inside the battery container 300, and a surface portion 342 is outside the battery container 300, so that the melting portion 340 has a left-right direction. The sheet thickness t is expanded. Thereby, the boundary part including the boundary line L1a formed between the fusion part 340 and the non-fusion part in the battery container 300 has an arc shape that is longer than the plate thickness t and longer than the straight line. Therefore, even if the boundary portion has low strength, the strength is enhanced by lengthening the boundary portion, and the force and time required for breaking increase, so that the reliability of the fusion zone 340 is improved.

  (2) Since the optical axis LC (center line) of the irradiation laser beam L2 passing through the convex end portion 341 is within 0.3 mm with respect to the contact portion 330 inside the battery container 300, the position from the front end portion 341 is reduced. The length of the boundary line L1a at the boundary between the fused portion 340 and the non-fused portion up to the side surface 310b as the side surface portion can be made longer.

  (3) Since the width of the fusion portion 340 is less than 90 degrees relative to the direction in which the outside of the battery container 300 is viewed from the contact portion 330 inside the battery container 300, the fusion portion 340 reaching the side surface 310b from the tip 341. And the boundary line L1a between the metal and the non-melted portion can be lengthened.

  (4) With the X-ray CT apparatus 600, it is possible to obtain a CT image in a form in which the restrictions on the imaging conditions are relaxed and the time required for the imaging is reduced to the same level as in the related art. For example, restrictions or limitations in the evaluation method described in Patent Document 1 described above, such as omitting or simplifying the steps of placing a battery in water in a water tank and having to bring an ultrasonic sensor close to a battery container, for example. be able to.

(5) The length of the boundary line L1a can be long. For example, the predetermined length can be the plate thickness t of the battery container 300 constituting the side surface or the plate thickness of the lid 320.
(6) Even if a change occurs in the relationship between the light and dark value and the melt depth due to the state of the material, the shape and output of the laser beam, the relationship between the light and dark value and the melt depth is corrected by comparison at the correction timing, and this correction is performed. Since the energy intensity of laser light irradiation is controlled by the relationship between the brightness value and the melting depth, laser welding can be suitably performed.

  (7) By using the X-ray CT apparatus 600, the melting depth can be measured with high accuracy by nondestructive inspection without mechanical deformation. In addition, in the case of a nondestructive inspection that does not require a cutting interval or a cutting margin, a continuous inspection can be performed in a direction in which the state of the fusion zone 340 extends. In particular, it has been newly found that the range in which the density change has changed by resolidification can be clearly measured by the X-ray CT apparatus 600. With the X-ray CT apparatus 600, it is possible to acquire a CT image in a manner in which the regulation on the imaging conditions is suppressed and the time required for the imaging is suppressed to the same level as in the related art.

  (8) By continuously monitoring the light emission image of the image over the entire circumference of the contact portion 330 in the circumferential direction, a failure of the contact portion 330 of the battery container 300 may be overlooked by cutting at predetermined intervals. Even a certain defect can be detected.

  (9) The laser beam applies energy on average to the corresponding irradiation area of the top hat type to enable stable welding processing, and its control is easy, and the laser beam of the corresponding irradiation area of the Gaussian type is easily applied. A reliable welding process with high energy can be performed at the center.

(Other embodiments)
This embodiment can be implemented with the following modifications. The present embodiment and the following modifications can be implemented in combination with each other within a technically consistent range.

  -In the said embodiment, the case where one "melting depth-brightness-darkness relationship curve" was provided about the battery 30 was illustrated. However, the present invention is not limited to this, and the “melting depth-brightness / darkness relationship curve” may be set for each welding position of the case, or may be set for each welding section, which is a section provided by dividing the entire circumference of the contact portion into several sections. It may be set. Even if the relationship between the light and dark value and the melting depth varies depending on the welding position and welding section of the battery container as the welding target, since the relationship between the light and dark value and the melting depth is determined at these welding positions, etc. Appropriate welding can be performed at a position or the like.

  -In above-mentioned embodiment, the case where welding control part 500 adjusts the output of laser oscillator 110 was illustrated. However, the present invention is not limited to this, and the welding control unit may adjust the applied energy in other modes as long as the energy applied to the welding target portion can be adjusted. For example, the energy amount may be adjusted by controlling the optical system of the laser output unit or by changing the distance to the battery to change the irradiation range of the laser light. Further, the energy amount may be adjusted by changing the relative speed of the laser beam by controlling the relative speed between the laser output unit and the battery. That is, the melting depth is maintained or changed by adjusting the amount of energy applied to the laser irradiation location.

In the above configuration, the oscillation laser light L0 may be a laser light other than the semiconductor laser, for example, a laser light such as a high-brightness YAG laser.
-In the said embodiment, the case where an example of the energy intensity distribution D6 of the irradiation laser beam L2 was a top hat type + Gaussian type was illustrated. However, the present invention is not limited to this, and the intensity distribution of the energy of the laser beam may be mainly a Gaussian type, mainly a top hat type or the like. When a Gaussian laser is used, the irradiation range is narrowed and energy is easily concentrated, so that the time required for forming a keyhole can be shortened, and the time required for laser welding can be shortened.

  -In the above-mentioned embodiment, the case where case 310 and lid 320 were made of aluminum (including aluminum alloy) was illustrated. However, the present invention is not limited to this, and the case and the lid may be made of a metal material other than aluminum, such as an alloy such as iron, copper, and stainless steel. Any metal material other than aluminum can be used as long as it can be used as a container and can be welded by laser light. Thereby, the degree of freedom in designing the battery case and lid can be improved.

  In the above embodiment, the welding control unit 500 adjusts the amount of energy to be applied while determining the brightness value of the laser irradiation location that dynamically changes in the welding process (indirectly determining the melting depth). The case has been exemplified. However, the present invention is not limited to this. After welding one battery or after welding a predetermined section of the abutting portion, the welding control unit performs welding of the next battery or the next based on the brightness value of the welded portion. Feedback control may be performed so as to adjust the energy intensity applied when welding the section. This makes it possible to reduce the load of acquiring and calculating the light and dark values.

  -In the above-mentioned embodiment, the case where contact part 330 which extends in the up-and-down direction by fitting lid 320 in opening 310c of case 310 was provided was illustrated. However, the present invention is not limited to this, and the contact portion 330 may be provided in the horizontal direction by being provided so as to cover the side end portion 310 a around the opening 310 c of the case 310. At this time, the laser welding may be performed such that the direction in which the contact portion extends is the laser irradiation direction. At this time, the side surface of the case forms a laser-welded plane, and the end of the outer peripheral portion of the lid forms a side surface with respect to the laser-welded plane.

  In the above-described embodiment, the timing at which the laser welding of the battery 30 is performed is set as the correction timing. However, the correction timing may be set after a lapse of a predetermined time after the laser welding of the battery 30 is performed.

  In the above embodiment, the case where the case 310 and the lid 320 of the battery container 300 are welded is exemplified. However, the present invention is not limited thereto. It may be a welding target.

  Numeral 30: battery, 110: laser oscillator, 200: laser output unit, 250: condenser lens, 260: collimating lens, 261: intensity distribution converter, 300: battery container, 310: case, 310a: side end, 310b Side surface, 310c opening, 320 lid, 320a surface, 320b outer peripheral portion, 330 contact portion, 331 remaining portion, 340 melting portion, 340B melting portion, 341 tip portion, 342 surface Part, 350: molten pool, 350A: luminescent image, 350A-350D: luminescent image, 350B: luminescent image, 350C: luminescent image, 350D: luminescent image, 400: spectroscope, 440: imaging unit, 500: welding control unit, 510: image acquisition unit, 520: luminescence image extraction unit, 530: fusion depth determination unit, 540: storage unit, 541: determination data, 542: luminescence image data, 600: X-ray T device, 610: imaging unit, 611: sample stage, 620: imaging control unit, 630: storage unit, 635A: welding position, 635A-635D: welding position, 635B: welding position, 635D: welding position, 700: judgment data Management device, 710: determination control unit, 711: CT determination unit, 712: determination data update unit, 720: storage unit, 721: emission image data, 722: CT image data, 723: reference data, α: angle, t ... Plate thickness, Da to Dd: melting depth, Dx: melting depth, E1: light, W: case side width, L0: oscillation laser light, L1: parallel light, L2: irradiation laser light, L3: converted laser light.

Claims (12)

A secondary battery including a battery container in which an opening of a metal case containing a power generation element is sealed with a metal lid,
A peripheral contact portion between the opening of the case and the outer peripheral portion of the lid body includes a fusion portion that is melted in a circumferential direction of the contact portion by laser welding.
In the cross section orthogonal to the circumferential direction, the melted portion is a convex region in which the region melted by the laser welding has a front end portion which is reduced inward from the outer surface of the battery container and directed inward. hand,
In the cross section orthogonal to the circumferential direction, the convex shape has the tip portion facing the contact portion inside the battery container, and the outer surface portion of the battery container has a laser for laser welding. It spreads to the left and right of the position where the light was irradiated,
The tip has not reached the inside of the battery container,
In the secondary battery, the surface portion has one of the left and right sides of the cross section reaching a side surface with respect to the laser-welded plane outside the battery container. 2. The secondary battery according to claim 1, wherein the convex shape has a center line extending from the surface portion toward the tip portion within 0.3 mm from the contact portion inside the battery container. 3. When the fusion portion is viewed from the contact portion inside the battery container, the boundary portion with the non-fusion portion reaching the side surface from the tip portion of the convex shape, the direction in which the surface portion is seen. 3. The secondary battery according to claim 2, wherein the secondary battery is disposed in a range of less than 90 degrees on the side surface side of the center line. A battery container for a secondary battery in which an opening of a metal case is sealed by a metal lid, and a circumferential contact portion between the opening of the case and an outer periphery of the lid. An inspection method for inspecting a battery container having a molten portion that is melted in a circumferential direction extending the contact portion by laser welding with laser light,
The cross section of the fusion zone, for the cross section orthogonal to the circumferential direction, to obtain an image including a region fused by the laser welding,
Based on the obtained image, the region melted by the laser welding is a convex region having a tip portion that is reduced inward from the outer surface of the battery container toward the inside and faces inward, and the convex shape is In a cross section orthogonal to the circumferential direction, the front end portion is directed to the contact portion inside the battery container, and the outer surface portion of the battery container is left and right of a position irradiated with the laser beam. The front end portion has not reached the inside of the battery container, and the surface portion has one of the left and right sides of the cross section reaching a side surface with respect to the laser-welded plane outside the battery container. Inspection method of battery container inspection method. The method for inspecting a battery container according to claim 4, wherein an image including an area melted by the laser welding is acquired by an X-ray CT apparatus. In the inspection, when the convex boundary line reaching the side surface is equal to or longer than a predetermined length, and when the outside of the battery container is viewed from the abutting portion inside the battery container, The inspection method of the battery container according to claim 5, wherein the inspection is performed to determine whether or not the projection is disposed within a range of less than 90 degrees from the center line of the convex shape to the side surface in the viewing direction. The inspection method for a battery container according to claim 6, wherein the predetermined length is a shortest distance from the tip portion of the convex shape to the side surface of the battery container. A method for manufacturing a secondary battery including a battery container that is laser-welded in a manner capable of changing the energy intensity irradiated with laser light,
In an image acquisition unit, an image at the irradiation position of the laser light and its periphery is acquired,
Extracting an emission image of the image by an extraction unit,
In the control unit, from the emission image of the image, and the relationship between the brightness value and the melting depth set in advance in the storage unit, the laser light is irradiated such that the melting depth becomes a predetermined depth. Control the energy intensity
In the correction unit, to correct the relationship between the brightness value and the melting depth is set in advance in the storage unit,
The correction unit compares the melting depth of the laser beam irradiation location at a past correction timing with the emission image of the image at the past correction timing, and sets the brightness value preset in the storage unit. And a method for manufacturing a secondary battery for correcting the relationship between the melting depth and the melting depth. The method for manufacturing a secondary battery according to claim 8, wherein the melting depth of the laser beam irradiation location is measured by a nondestructive inspection using an X-ray CT apparatus. The method for manufacturing a secondary battery according to claim 8, wherein the relationship between the brightness value and the melting depth is determined for each welding position or welding section of the welding target. In the secondary battery including the battery container in which the opening of the metal case accommodating the power generation element is sealed by a metal lid, the irradiation part of the laser light may include the opening of the case and the lid. A circumferential abutment with the outer periphery of the body,
The determining unit obtains a fusion depth over the entire circumference of the contact portion from the relationship between the brightness value and the fusion depth based on the light emission image of the image acquired over the entire circumference of the contact portion. The method for manufacturing a secondary battery according to any one of claims 8 to 10, wherein it is determined whether or not the melting depth over the entire circumference is appropriate. The laser beam is composed of a first laser beam having a Gaussian intensity distribution and a second laser beam having an irradiation diameter larger than that of the first laser beam and having a top-hat intensity distribution. 12. A laser beam generated by performing the above operation, wherein the laser beam has a distribution in which the intensity of the generated laser beam has a maximum value in a central portion surrounded by a peripheral portion. The method for producing a secondary battery according to claim 1.