Measurement method and test machine

Abstract

A method for measuring the vector field of particles ejected upon the occurrence of a thermal event in a battery cell according to a disclosed embodiment comprises: a step of acquiring a first image from a first camera that captures the particles; a step of acquiring a second image from the first camera after acquiring the first image; a step of matching the first image and the second image based on a PIV technique; and a step of calculating vector field data of the particles from the matching result of the first image and the second image.

Description

Technology Field

[0001] The present invention relates to a measurement method and a test device. Background Technology

[0002] With the rapid increase in demand for portable electronic products such as laptops, video cameras, and mobile phones, and the full-scale commercialization of robots and electric vehicles, research on high-performance secondary batteries capable of repeated charging and discharging is actively underway.

[0003] Currently commercialized rechargeable batteries include nickel-cadmium, nickel-hydrogen, nickel-zinc, and lithium-ion batteries. Among these, lithium-ion batteries are gaining attention for their advantages, such as the ability to charge and discharge freely with almost no memory effect compared to nickel-based batteries, a very low self-discharge rate, and high energy density.

[0004] Recently, secondary batteries are widely used for driving or energy storage not only in small devices such as portable electronic devices but also in medium-to-large devices such as electric vehicles and Energy Storage Systems (ESS). These secondary batteries can form a single battery module by housing multiple batteries together inside a module case while electrically connected. Furthermore, multiple such battery modules can be connected to form a single battery pack.

[0005] However, when multiple secondary batteries (battery cells) or battery modules are densely packed in a confined space as described above, they may be vulnerable to thermal events. In particular, if an event such as thermal runaway occurs in a single battery cell, high-temperature gases, flames, or heat may be generated. If these gases, flames, or heat are transferred to other battery cells within the same battery module, an explosive chain reaction situation, such as thermal propagation, may occur. Furthermore, such a chain reaction can not only cause accidents such as fire or explosion in the affected battery module but also trigger fires or explosions in other battery modules.

[0006] Furthermore, in the case of medium to large battery packs, such as those found in electric vehicles, the risk of thermal chain reactions can be even greater because they contain a large number of battery cells and modules to increase output and / or capacity. In addition, users, such as drivers, may be present in the vicinity of battery packs installed in electric vehicles. Therefore, if a thermal event originating in a specific battery module is not properly controlled and triggers a chain reaction, it can result in significant property damage as well as loss of life.

[0007] To suppress or control thermal events in multiple battery cells, it is first necessary to quantitatively measure and analyze the flame propagation speed, flame direction, and flame ejection speed in a single battery cell. The problem to be solved

[0008] The present invention aims to solve the aforementioned problems and other problems.

[0009] Another objective of the present invention may be to provide a measurement method and a test device for quantitatively analyzing thermal events of a battery cell using the Particle Image Velocimetry (PIV) technique.

[0010] Another objective of the present invention may be to provide a measurement method and a test device that apply the PIV technique using flammable particles emitted by a battery cell and particle seeds distinguished from the flammable particles. means of solving the problem

[0011] A method for measuring the vector field of particles ejected upon the occurrence of a thermal event in a battery cell according to a disclosed embodiment comprises: a step of acquiring a first image from a first camera that captures the particles; a step of acquiring a second image from the first camera after acquiring the first image; a step of matching the first image and the second image based on a PIV technique; and a step of calculating vector field data of the particles from the matching result of the first image and the second image.

[0012] The method may further include the step of irradiating a laser toward the particle before acquiring the first image.

[0013] The step of calculating the vector field data of the above particles can be obtained by distinguishing between the particles irradiated by the laser and the particles not irradiated by the laser.

[0014] The wavelength of the above laser may be configured to be between 522 nm and 542 nm.

[0015] The light emitted by the above laser can be configured to form a laser 2D sheet.

[0016] The method may further include the step of acquiring a third image from a second camera that photographs the particle; the step of acquiring a fourth image from the second camera after acquiring the third image; the step of matching the third image with the fourth image; and the step of calculating vector field data of the particle from the matching result of the third image and the fourth image.

[0017] The first camera above can acquire an image through a bandpass filter.

[0018] A test device for testing a battery cell according to another disclosed embodiment comprises: a case for housing the battery cell and a holder having an opening formed in the case and exposing at least a portion of the battery cell; a light source providing light around the opening; a camera detecting the surroundings of the opening; and a processor controlling the light source or the camera.

[0019] The above holder may include a heater located inside the case and in contact with the battery cell.

[0020] The above holder can guide venting gas or flammable particles to be discharged through the opening when a thermal event occurs in the battery cell.

[0021] The above holder may include an insulating member configured to surround the battery cell.

[0022] The above opening can expose the terrace portion of the battery cell.

[0023] The width of the above opening may be smaller than the width of the battery cell.

[0024] The height of the above opening may be smaller than the height of the battery cell.

[0025] A test device according to another disclosed embodiment comprises: a chamber in which a battery is provided to generate a thermal event of the battery; a first camera that applies a bandpass filter and photographs the interior of the chamber; a second camera that does not apply the bandpass filter and photographs the interior of the chamber; a laser light source that emits a laser into the interior of the chamber; and a processor that calculates vector field data from an image captured by the camera based on a PIV technique and generates the propagation speed of a particle generated from the thermal event of the battery based on the calculated vector field data.

[0026] The processor can perform preprocessing of images captured by the first camera and the second camera, set image fragments in the preprocessed images, perform image evaluation to match each image fragment, and after image evaluation, perform vector field data processing of particles included in the matched image fragments.

[0027] The above processor can adjust vector field data based on data interpolation or data smoothing.

[0028] The above processor can output to the user the propagation speed of the particle calculated based on the adjusted vector field data. Effects of the invention

[0029] The measurement method and test device according to one disclosed embodiment have the effect of not requiring a separate particle to track the vector field in order to measure the velocity of gas ejection or flame ejection occurring during the thermal runaway process of a battery, by observing a particle measuring the flow to visualize an invisible vector field and measuring the velocity thereof.

[0030] In particular, the measurement method and test device according to the disclosed embodiment can more accurately measure the speed and direction of fuel by applying the PIV technique of a droplet that is atomized when fuel is injected.

[0031] In addition, the measurement method and test device according to the disclosed embodiment have the effect of enabling the derivation of a velocity field in a 2D plane within a laser sheet and reducing errors in the self-emission of flames in 3D images. Brief explanation of the drawing

[0032] FIG. 1 is a schematic diagram showing a test device according to one embodiment of the present invention. FIG. 2 is a flowchart regarding a method for a disclosed test device to measure thermal runaway of a battery. FIGS. 3, FIGS. 4, and FIGS. 5 are drawings for specifically explaining the image processing of FIGS. 2. FIG. 6A is a diagram exemplarily showing particles in a flame used in a measurement method according to one embodiment, and FIG. 6B is a diagram exemplarily showing particles in a flame irradiated with a laser. FIG. 7 is a diagram exemplarily showing a measurement method according to one embodiment in which a filter is applied. FIG. 8 is a schematic diagram showing a test device according to another embodiment. Figure 9 is a diagram showing that a thermal event occurred from a single battery cell. FIGS. 10 and FIGS. 11 are drawings showing a battery cell (10) used in a test device according to another embodiment. FIG. 12 is a drawing showing a battery cell (10) coupled to a holder (200) of a test device according to another embodiment. FIG. 13 is a schematic diagram showing part of the cross-sectional configuration along the cutting line A-A' of FIG. 12. FIG. 14 is a schematic diagram showing part of the cross-sectional configuration along the cutting line B-B' of FIG. 12. FIG. 15 is a diagram showing the process of a thermal event proceeding from a battery cell (10) used in a test device. FIG. 16 is a diagram exemplifying a thermal event being processed by PIV by a test device. FIGS. 17 and FIGS. 18 are schematic drawings of a test device according to another embodiment of the present invention. Specific details for implementing the invention

[0033] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, and should be interpreted in a meaning and concept consistent with the technical spirit of the present invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0034] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all aspects of the technical concept of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0035] FIG. 1 is a schematic diagram showing a test device according to one embodiment of the present invention.

[0036] Referring to FIG. 1, the test device may be composed of a chamber (100) including a battery (10) that generates a flame, a support member (102) that supports the battery (10), and an outlet (101) that discharges gases, etc., generated as the battery (10) deteriorates. Additionally, the test device may include at least two cameras (310, 320) for capturing the flames emitted as the battery (10) deteriorates, and a laser light source (400) that irradiates a laser at the location where gas and flames are emitted from the battery (10).

[0037] The laser light source (400) can irradiate a laser at a location where gas and flame are emitted from the battery (10). Specifically, the laser light source (400) can output light to form a laser 2D sheet (410) in the chamber (100). For example, the wavelength of the light output by the laser light source (400) may be 532 nm. The reason the disclosed test device includes a laser light source (410) that forms a laser 2D sheet is to acquire an image even when a thermal event occurs in which the battery (10), which is the test subject, emits only gas without flame. That is, even when the battery (10) emits gas, the test device may measure the propagation and ejection speed of the flame based on an image captured by a camera (310, 320) that captures it through a self-emitting device.

[0038] Meanwhile, the disclosed test device can observe gases and particles that occur immediately before the ignition of the battery (10) through a laser light source (400). That is, conventional techniques for measuring thermal runaway of batteries often implement the propagation and ejection speed of flames by applying engine visualization techniques. However, the disclosed test device enables the application of the PIV (Particle Image Velocimetry) technique described later by allowing particles and gases to be clearly observed in the camera image captured in a dark screen even at the beginning of the battery's thermal runaway through a laser.

[0039] The test device may include at least two high-speed cameras (310, 320). In this case, a bandpass filter of 522 to 542 nm may be applied to the first camera (310). As a result, the acquired first image (321) may appear green. The second camera (320) may not have a bandpass filter applied. The second image (321) captured by the second camera (320) may be a normal color image.

[0040] Meanwhile, the disclosed test device does not necessarily need to apply a bandpass filter to the first camera (310). Since the disclosed test device measures the ejection velocity based on particles contained in an image of a flame or gas, it is sufficient to include at least one camera that acquires an image of particles being emitted.

[0041] When a bandpass filter is applied to the first camera (310), there is an advantage in that particles generated when a battery ignites can be distinguished more clearly. Since the flame itself often exists at a wavelength of 532 nm, there may be no problem in acquiring an image even without irradiating with a 532 nm laser. However, since the brightness intensity is lower compared to particles and gases directly irradiated by the laser, using the first camera with a bandpass filter applied allows for the acquisition of an image in which particles can be distinguished more clearly.

[0042] The test device may include additional configurations other than those shown in FIG. 1. For example, the test device may further include a user terminal (e.g., a computer) that performs image processing and data processing after receiving an image captured by the camera (310, 320). Below, the configuration that measures the velocity of particles generated from the thermal runaway of the battery (10) through the image captured by the camera (310, 320) will be referred to as a processor and described later.

[0043] FIG. 2 is a flowchart regarding a method for a disclosed test device to measure thermal runaway of a battery.

[0044] Referring to FIG. 2, the test device acquires images from the first camera (310) and the second camera (320) (20).

[0045] Here, the images (310, 321) obtained from the first camera (310) and the second camera (320) are images containing particles ejected through the laser light source (400). That is, the disclosed test device does not require separate particles to be floated or to follow the flow in order to measure the ejection speed of gas and flames generated during the thermal runaway process of the battery.

[0046] The test device performs image processing on the acquired image (30).

[0047] Particle Image Velocimetry (PIV) is a non-coherent vector field measurement method that visualizes invisible fluid flow by floating flow-following particles in the flow, observing them, and measuring their velocity. The principle of the PIV technique is to determine the distance of each particle within an image by comparing frames captured at regular time intervals, and then calculate the velocity by dividing the distance by the unit time during which the frame was captured.

[0048] The disclosed test device measures the velocity of particles generated from a thermal event, i.e., the vector field, based on the aforementioned PIV technique. To use this PIV technique, the test device performs image processing captured from cameras (310, 320). Image processing is carried out by the processor described in FIG. 1, and the processor performs image preprocessing, image evaluation, and vector field derivation. The specific method by which the processor performs image processing will be described later through the drawings below, such as FIG. 3.

[0049] After performing image processing, the test device determines the flame ejection and propagation speed (40). It outputs the measurement result of the determined propagation speed (50).

[0050] Specifically, the measurement results output by the test device can vary. For example, the test device may simply output an average value of the propagation speed or a numerical value of the propagation speed of each particle or a designated area, or it may output an image that converts particles contained in the flame into vectors, such as in FIG. 16.

[0051] FIGS. 3, 4, and 5 are drawings for specifically explaining the image processing of FIG. 2. To avoid redundant explanations, they are described together below.

[0052] Referring to FIG. 3, the test device loads an image (31).

[0053] According to one example, the image processing program used by the test device may be a PIVLab or Matlab program. The test device loads the original image captured by the first camera (310) or the second camera (320) of FIG. 1 into the aforementioned image processing program and performs the following image processing.

[0054] First, the test device performs image preprocessing (32).

[0055] Image preprocessing refers to enhancing image readability, removing background noise, and adjusting image brightness. In addition to the aforementioned techniques, the test device may perform various other image preprocessing steps.

[0056] Once image preprocessing is complete, the test device performs image evaluation (33).

[0057] Specifically, the image evaluation selects an image processing area, namely an Interrogation Area. Referring to FIG. 4, the Interrogation Area is each image segment (305) divided from the third image (301) and the fourth image (302), which correspond to different frames captured by a single camera. The test device determines the size of the image area (305) through a preset standard in the images (301, 302) captured with a time difference.

[0058] Meanwhile, the PIV technique utilizes cross-correlation. Accordingly, the test device finds the image fragment most similar to the third image (301) in the fourth image (302) based on the image fragment (305) selected from the third image (301). In order to accurately match these similar image fragments, the distinction between each image (301, 302) must be clear, and to this end, the test device performs a range description and pattern matching. In particular, the test device disclosed for pattern matching may also match the patterns of each image (301, 302) through a discrete cross-correlation function.

[0059] The function for pattern matching of image fragments (305) in the disclosed test device may use the following mathematical formula 1.

[0060]

[0061] The test device may also use the Fast Fourier Transform to quickly calculate the function of Equation 1.

[0062] Referring again to FIG. 3, when the image evaluation is completed, the test device derives a vector field for the movement of the particles (303 in FIG. 4) of each image (34).

[0063] As described above, the PIV technique detects similar image regions of the third image (301) and the fourth image (302), and then calculates the movement of the particles, i.e., the vectors, through the particles included in the matched image regions. To this end, the test device can perform data verification, data interpolation, and data smoothing.

[0064] Referring to FIG. 5, the test device can perform data interpolation to derive a vector field. Specifically, data interpolation means data processing that determines a region (350) among the vectorized regions that has no vector value and generates a new vector value (351) based on the vector value of the surrounding image region.

[0065] To derive a vector field, the test device can perform data smoothing. That is, if a vector value (352) that is significantly different from a surrounding area is found, the test device can perform data smoothing to adjust the vector value (353) to a level similar to that of a nearby vector value.

[0066] The test device calculates the final flame ejection and propagation speed through the data processing described in Fig. 5.

[0067] The test device verifies the validity of the output result (35).

[0068] Specifically, the test device verifies the results of flame ejection and propagation speeds using vector values ​​through boundary detection of the captured image, and this can be verified through a conventional general image comparison process.

[0069] Meanwhile, the test device can derive various quantitative indicators based on the velocity component (u, v) included in the vector value. For example, the test device can output various indicators as measurement results, such as mean velocity, minimum velocity, maximum velocity, turbulent kinetic energy (TKE), vortex position, velocity distribution (contour), or TKE distribution (contour).

[0070] FIG. 6A is a diagram exemplarily showing particles in a flame used in a measurement method according to one embodiment, and FIG. 6B is a diagram exemplarily showing particles in a flame irradiated with a laser.

[0071] Referring to FIG. 6A, the battery (10) can emit flames and particles together during thermal runaway. Due to the light provided by the flames, images of particles present within the flames can be obtained. As a result, the disclosed test device can obtain images without having to provide observation particles required when applying the PIV technique.

[0072] Referring to Figure 6B, when a bandpass filter is applied, the distinction between particles can be made more clearly. Due to the light provided by the flame, particles not exposed to the laser can be distinguished with relatively low brightness.

[0073] FIG. 7 is a diagram exemplarily showing a measurement method according to one embodiment in which a filter is applied.

[0074] Referring to FIG. 7, when a bandpass filter is applied, the brightness of the flame can be significantly reduced. As a result, particles exposed to the laser and particles not exposed can be distinguished more clearly. That is, the test device can more clearly distinguish particles caused by the flame from an image obtained through the first camera (310) with the bandpass filter applied, and thereby measure the propagation speed.

[0075] FIG. 8 is a schematic diagram of a test device according to another embodiment. FIG. 9 is a diagram showing a thermal event occurring from a single battery cell. FIG. 10 and FIG. 11 are diagrams showing a battery cell (10) used in a test device according to another embodiment. To avoid redundancy, they are described together below.

[0076] Referring to FIGS. 8 and 9, a test device according to another embodiment may include a holder (200), a light source (400), a camera (310, 320), and a processor (not shown).

[0077] A single cell of a battery (10 in FIG. 10) may refer to a secondary battery. In this case, the battery cell (10) may be a pouch battery cell having a rectangular shape. However, the battery cell used in the test device is not limited in shape and may be a cylindrical battery cell having a cylinder shape or a rectangular battery cell having a rectangular shape.

[0078] The holder (200) may include a case (230 in FIG. 12) that accommodates a battery cell (10). The case (230) may have an opening (201) that exposes at least a portion of the battery cell (10). When a thermal event occurs in the battery cell (10), a flame (f), venting gas (g), or flammable particles (s) may be discharged through the opening (201).

[0079] The chamber (100) may provide an internal space. A holder (200) may be accommodated in the chamber (100). The chamber (100) may be made of a light-transmitting material or a transparent material. The chamber (100) may restrict the wide spreading of flames (f), venting gases (g), or flammable particles (s) emitted from the battery cell (10).

[0080] The light source (400) may be located outside the chamber (100). The light source (400) may provide light around the opening (201). The light source (400) may be the laser light source described in FIG. 1. For example, the light source (400) may be a laser light source that provides green light. The light source (400) may provide light to the flame (f), venting gas (g), or flammable particles (s) that are discharged through the opening (201).

[0081] The camera (310, 320) may be located outside the chamber (100). The camera (310, 320) may be the same as the embodiment described in FIG. 1, etc. The camera (310, 320) may detect the surroundings of the opening (201) and may detect light reflected by flame (f) and ignitable particles (s) emitted through the opening (201).

[0082] Specifically, the camera (310, 320) may have a resolution of 1280x704 or higher. Additionally, the camera (310, 320) may have a shooting speed of 8000fps. Additionally, the camera (310, 320) may be operated with an exposure time of 20 microseconds.

[0083] The processor may be connected to the light source (400) or camera (310, 320) via a wired or wireless connection. The processor may control the light source (400) or camera (310, 320). For example, the processor may be a computer or a control device. Additionally, the processor may be composed of multiple parts.

[0084] In addition to the test device according to the disclosed embodiment, when ignition of the battery cell (10) or a thermal event occurs in the battery cell (10), the processor can acquire data on the development of the thermal event using the Particle Image Velocimetry (PIV) technique. For example, the processor can detect light reflected by the ignitable particle(s) through the camera (310, 320), acquire an image, and calculate the vector field of the ignitable particle(s). Furthermore, the propagation of the flame (f) can be calculated by approximating or assuming the movement of the ignitable particle(s) as the movement of the flame (f). Additionally, based on the vector field data of the ignitable particle(s), the velocity distribution of the ignitable particle(s) over time and the turbulent velocity of the ignitable particle(s) can be calculated.

[0085] Referring to FIGS. 10 and 11, the battery cell (10) used in the test device may include a body (13), an electrode lead (11), or a terrace portion (12).

[0086] The body (13) may include an electrode assembly. The body (13) may extend in the front-rear direction or the X-axis direction. The electrode lead (11) may protrude from the body (13).

[0087] The electrode leads (11) may be configured as a pair and may protrude from the body (13) in the forward and backward direction or in the X-axis direction.

[0088] The terrace portion (12) may be formed along the perimeter of the body (13). The terrace portion (12) may protrude in the front-rear direction or the X-axis direction of the body (13). The terrace portion (12) may be configured to surround the electrode lead (11). Additionally, the terrace portion (12) may protrude upward from the body (13).

[0089] If an abnormal condition occurs in the battery cell (10) due to overheating or overcharging, swelling may occur. At this time, the battery cell (10) may swell in the left-right direction or the Y-axis direction. If the swelling phenomenon intensifies, the battery cell (10) may emit venting gas (g). Additionally, the battery cell may emit flames (f) and flammable particles (s). When a thermal event occurs, the battery cell (10) may emit venting gas (g), flames (f), or flammable particles (s) in random directions. Therefore, appropriate control is required to ensure that the battery cell (10) emits venting gas (g), flames (f), or flammable particles (s) within the detection range of the camera (310, 320) and the light supply range of the light source (400).

[0090] FIG. 12 is a drawing showing a battery cell (10) coupled to a holder (200) of a test device according to another embodiment. FIG. 13 is a schematic drawing showing part of a cross-sectional configuration along the cutting line A-A' of FIG. 12. FIG. 14 is a schematic drawing showing part of a cross-sectional configuration along the cutting line B-B' of FIG. 12. Referring to FIG. 12 to FIG. 14, the holder (200) of the test device may include a case (230), a heater (210), and an insulating member (220).

[0091] The heater (210) may be located inside the case (230). The heater (210) may be in contact with, coupled to, or attached to at least one surface of the battery cell (10). The heater (210) may apply heat to the battery cell (10) to cause a thermal event of the battery cell (10).

[0092] The insulating member (220) may be located inside the case (230). The insulating member (220) may be arranged to surround the battery cell (10) and the heater (210) along the perimeter of the case (230). The insulating member (220) may be made of a material with high thermal insulation properties. The insulating member (220) may suppress the propagation of heat generated from the battery cell (10) and the heater (210).

[0093] The case (230) may have an opening (201) in the front or X-axis direction. The opening (201) may expose at least a portion of the front side or terrace portion (12) of the battery cell (10). The case (230) and the insulating member (220) may secure the battery cell (10). As a result, swelling of the battery cell (10) may be suppressed even if the heater (210) applies heat to the battery cell (10). Additionally, the battery cell (10) may be secured or pressurized in the left-right direction or Y-axis direction. Additionally, the battery cell (10) may be secured or pressurized in the up-down direction or Z-axis direction. As a result, venting gas (g), flame (f), or flammable particles (s) generated from the battery cell (10) may be guided to be discharged in the front-back direction or X-axis direction. Accordingly, venting gas (g), flame (f) or flammable particles (s) can be discharged forward or in the X-axis direction through the opening (201).

[0094] The case (230) may include a front plate. The front plate may have an opening (201). The opening (201) may expose the terrace portion (12) of the battery cell (10). Additionally, the electrode lead (11) and the terrace portion (12) of the battery cell (10) may protrude outside the case (230) through the opening (201). The opening (201) may be formed in a rectangular shape. The width (D1) in the left-right direction or the width (D1) in the Y-axis direction of the opening (201) may be formed smaller than the width (D1) in the left-right direction or the width (D1) in the Y-axis direction of the battery cell (10). Additionally, the height (D3) in the up-down direction or the height (D3) in the Z-axis direction of the opening (201) may be formed smaller than the height (D4) in the up-down direction or the height (D4) in the Z-axis direction of the battery cell (10). As a result, the front plate of the case (230) can fix or press the battery cell (10) in the forward and backward direction or in the X-axis direction.

[0095] FIG. 15 is a diagram showing the process of a thermal event proceeding from a battery cell (10) used in a test device. FIG. 16 is a diagram exemplarily showing a thermal event being processed by PIV by the test device.

[0096] Referring to FIGS. 15 and 16, the processor of the test device can control the camera (310, 320) to detect flammable particles(s) emitted from the opening (201) when a thermal event occurs in the battery cell (10) and to acquire a first image.

[0097] When a thermal event occurs, the battery cell (10) can emit flammable particles (s). The test device can detect the flammable particles (s) and apply a PIV technique to the first image. The processor can obtain vector field data of the flammable particles (s) from the first image. Additionally, the ejection velocity of the flame (f) or the propagation velocity of the flame (f) can be calculated by approximating or assuming that the vector field data of the flammable particles (s) is the vector field data of the flame (f).

[0098] The camera (310, 320) of the disclosed test device may further include a filter (not shown) that passes light output by a light source (400). The filter may pass green light output by the laser light source (400). On the other hand, the filter may block orange light emitted from the flame (f). For example, the filter may be a band-pass filter that passes only green light. Accordingly, the processor can acquire an image using only the light reflected by the flammable particles (s). As a result, the accuracy of the PIV data of the flammable particles (s) can be improved.

[0099] FIGS. 17 and FIGS. 18 are schematic drawings of a test device according to another embodiment of the present invention.

[0100] Referring to FIGS. 17 and 18, a test device according to another embodiment may further include a plurality of particle seeds (600). The particle seeds (600) may refer to particles to be tracked in a PIV technique. The plurality of particle seeds (600) may be located inside a chamber (100). The plurality of particle seeds (600) may be distributed around an opening (201). When a thermal event occurs, the plurality of particle seeds (600) may be induced by venting gas (g), flame (f), or ignitable particles (s) emitted from a battery cell (10). As a result, the processor may control the camera (310, 320) to simultaneously detect the plurality of particle seeds (600) and the ignitable particles (s) to acquire a second image.

[0101] At this time, the plurality of particle seeds (600) may have different optical properties from the ignitable particles(s). The wavelength of light reflected by the plurality of particle seeds (600) and the wavelength of light reflected by the ignitable particles(s) may be configured to be different from each other. For example, the plurality of particle seeds (600) may be composed of a fluorescent material capable of reflecting or emitting light other than green light.

[0102] The processor can distinguish and obtain PIV data of multiple particle seeds (600) and PIV data of ignitable particles(s) from the second image. The processor can obtain flow information of venting gas (g) or flame (f) from the PIV data of multiple particle seeds (600). By simultaneously obtaining PIV data from multiple particle seeds (600) and PIV data from ignitable particles(s), the test device can detect and measure thermal events more accurately.

[0103] Meanwhile, although terms indicating directions such as up, down, left, right, front, and back have been used in this specification, these terms are used merely for convenience of explanation, and it is obvious to those skilled in the art that they may vary depending on the location of the object or the position of the observer.

[0104] As described above, although the present invention has been explained by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs. Explanation of the symbols

[0105] 10: Battery cell 11: Electrode lead 12: Terrace section 13: Body 100: Chamber 200: Holder 201: Opening 210: Heater 220: Insulating material 230: Case 310, 320: Camera 400: Laser light source 600: Particle Seed

Claims

Claim 1 A method for measuring the vector field of particles ejected when a thermal event occurs in a battery cell, comprising: a step of acquiring a first image from a first camera that captures the particles; a step of acquiring a second image from the first camera after acquiring the first image; a step of matching the first image and the second image based on a PIV technique; and a step of calculating vector field data of the particles from the matching result of the first image and the second image. Claim 2 A measurement method according to claim 1, further comprising the step of irradiating a laser toward the particle before acquiring the first image. Claim 3 In claim 2, the step of calculating the vector field data of the particle is a measurement method obtained by distinguishing between the particle irradiated by the laser and the particle not irradiated by the laser. Claim 4 A measurement method according to claim 2, wherein the wavelength of the laser is 522 nm to 542 nm. Claim 5 In claim 2, the light emitted by the laser is configured to form a laser 2D sheet. Claim 6 A measurement method according to claim 1, further comprising: a step of acquiring a third image from a second camera that photographs the particle; a step of acquiring a fourth image from the second camera after acquiring the third image; a step of matching the third image with the fourth image; and a step of calculating vector field data of the particle from the matching result of the third image and the fourth image. Claim 7 In claim 1, the first camera is a measurement method that acquires an image through a bandpass filter. Claim 8 A test device for testing a battery cell, comprising: a case for housing the battery cell and a holder having an opening formed in the case and exposing at least a portion of the battery cell; a light source that provides light around the opening and irradiates light onto particles ejected when a thermal event occurs in the battery cell; a camera that detects the surroundings of the opening and captures an image of the particles; and a processor that controls the light source or the camera and calculates vector field data from the image. Claim 9 In claim 8, the holder is a test device comprising a heater located inside the case and in contact with the battery cell. Claim 10 In claim 8, the holder is a test device that guides venting gas or flammable particles to be discharged through the opening when a thermal event occurs in the battery cell. Claim 11 In claim 8, the holder is a test device comprising an insulating member configured to surround the battery cell. Claim 12 In claim 8, the opening is a test device that exposes the terrace portion of the battery cell. Claim 13 In claim 8, the width of the opening is smaller than the width of the battery cell in the test device. Claim 14 In claim 8, the height of the opening is smaller than the height of the battery cell in the test device. Claim 15 A test device comprising: a chamber in which a battery is provided to generate a thermal event of said battery; a first camera that applies a bandpass filter and photographs the interior of said chamber; a second camera that does not apply the bandpass filter and photographs the interior of said chamber; a laser light source that emits a laser into the interior of said chamber; and a processor that calculates vector field data from an image captured by said camera based on a PIV technique, and generates the propagation speed of a particle generated from the thermal event of said battery based on said calculated vector field data. Claim 16 In claim 15, the processor performs preprocessing of images captured by the first camera and the second camera, sets image fragments in the preprocessed images, performs image evaluation to match each image fragment, and after image evaluation, performs vector field data processing of particles included in the matched image fragments. Claim 17 In claim 16, the processor is a test device that adjusts vector field data based on data interpolation or data smoothing. Claim 18 In claim 17, the processor is a test device that outputs to the user the propagation speed of the particle calculated based on adjusted vector field data.

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