Electrochemical reaction visualization device and electrochemical reaction visualization method

Abstract

To provide: an electrochemical reaction visualization device capable of easily discriminating between an active material and an electrolyte; and an electrochemical reaction visualization method.SOLUTION: An electrochemical reaction visualization device 100 according to the present disclosure, comprises: a cell 10 with a window, housing a secondary battery 1; a charge and discharge controller 20 that controls charging and discharging; a color confocal imaging part 30 that includes an objective lens 34 for transmitting a reflectance derived from an illumination light through reflection on the secondary battery 1; and an imaging processing part that acquires color image data and charging and discharging data in a charging state of the secondary battery 1. The image processing part includes: a master extraction part that selects the color image data in a full-charging state, extracts an active material part in the selected color image data, and extracts a range surrounding the active material part as a tracking ROI; and a slave extraction part that tracks a position of the extracted active material part in the color image data corresponded to each charging state, and extracts the range surrounding the tracked active material part as a tracking ROI.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrochemical reaction visualization device and an electrochemical reaction visualization method, and more particularly to a dynamic visualization device and a dynamic visualization method for visualizing the distribution of the state of charge of a secondary battery in which the active material and the electrolyte cannot be distinguished by color or brightness in an uncharged state.

[0002] Dynamic visualization of the state-of-charge distribution is necessary to evaluate the impact on secondary battery performance of factors such as the uniformity of electrochemical reactions inside the secondary battery, local overcharging, and physical changes such as temperature and expansion. [Background technology]

[0003] Patent Document 1 describes a method for evaluating the local state of charge of active material particles (graphite) in an electrolyte by utilizing the change in hue caused by a charge-discharge reaction. However, when the method of Patent Document 1 is applied to an all-solid-state battery, the solid electrolyte and the active material have similar hues at a certain state of charge (approximately 0% to 30%), making it difficult to distinguish and analyze them.

[0004] Patent Documents 2 to 5 describe observing lithium ion secondary batteries in charge and discharge states. However, as in Patent Document 1, when applied to all-solid-state batteries, the solid electrolyte and the active material have similar hues at a certain charge state, making it difficult to distinguish and analyze them. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5388078 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-239263 [Patent Document 3] Japanese Patent Application Publication No. 2017-212163 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-089969 [Patent Document 5] Japanese Patent Publication No. 2021-021579 Summary of the Invention [Problem to be solved by the invention]

[0006] In secondary batteries that use transparent electrolytes, such as conventional lithium-ion batteries, the electrolyte and active material can be easily distinguished during in-situ observation of charge and discharge states using a color confocal microscope. This is because the confocal optical system removes reflected light from the interface between the electrolyte and the observation window, allowing only the interfacial reflection between the electrolyte and active material to be observed. Since the space outside the active material particles in the electrode is porous, it is filled with electrolyte, and there is almost no reflected light from pores without active material. In this case, the active material and other areas can be relatively easily distinguished based on brightness and hue.

[0007] However, because the electrodes of all-solid-state batteries are a mixture of active material and solid electrolyte, when observing the reflected light at the electrode interface, both the active material and the solid electrolyte appear to have similar brightness. In particular, the active material in an uncharged state has a very similar brightness and hue to the solid electrolyte, making it difficult to distinguish them using conventional methods. In secondary batteries that use such solid electrolytes, it is not possible to evaluate the charge / discharge reactions of the electrodes using operando observation of the electrochemical reactions inside the battery. Therefore, a device and method for easily distinguishing between the active material and the (solid) electrolyte are desired.

[0008] The object of the present invention is to solve such problems and to provide an electrochemical reaction visualization device and an electrochemical reaction visualization method that can easily distinguish between active materials and electrolytes. [Means for solving the problem]

[0009] The electrochemical reaction visualization device according to the present disclosure is an electrochemical reaction visualization device for visualizing state changes during charging and discharging of a secondary battery, the electrochemical reaction visualization device including: a windowed cell having a transparent window and accommodating the secondary battery containing an active material whose luminance increases in a fully charged state; a charge / discharge controller that controls charging and discharging so that the secondary battery passes through a plurality of charge states with different charge amounts during the charge / discharge; a color confocal imaging unit that illuminates the secondary battery with illumination light through the transparent window and has an objective lens that transmits light reflected by the secondary battery from the illumination light, and acquires color image data of the secondary battery while changing the relative distance between the objective lens and the secondary battery; and a color confocal imaging unit that acquires color image data of the secondary battery while changing the relative distance between the objective lens and the secondary battery, the color confocal imaging unit acquiring color image data of the secondary battery at each charge state of the secondary battery. and an image processing unit that acquires the color image data of the fully charged state and the charge / discharge data for each charge state, the image processing unit having a link unit that associates the color image data and the charge / discharge data in chronological order, a master extraction unit that selects the color image data of the fully charged state, extracts a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as an active material portion, and extracts a range surrounding the active material portion as a tracking ROI, and a slave extraction unit that tracks the position of the extracted active material portion in the color image data corresponding to each charge state, and extracts a range surrounding the tracked active material portion as the tracking ROI.

[0010] In the electrochemical reaction visualization device, the image processing unit may further include a color analysis unit that converts the RGB brightness of the active material portion into a hue to analyze each state of charge.

[0011] In the electrochemical reaction visualization device, the master extraction unit may generate a master ROI including a plurality of the tracking ROIs, and generate a master mask from the generated master ROI in which the tracking ROIs are defined as valid regions and the regions other than the tracking ROIs are defined as invalid regions; and the slave extraction unit may generate a slave ROI including a plurality of the tracking ROIs, and generate a slave mask from the generated slave ROI in which the tracking ROIs are defined as valid regions and the regions other than the tracking ROIs are defined as invalid regions.

[0012] In the electrochemical reaction visualization device, the image processing unit may further include an overlap calculation unit that calculates the overlap of the tracking ROIs from the difference between the sum of the areas of the tracking ROIs included in the master mask or the slave mask that is used as a reference mask and the sum of the areas of the tracking ROIs included in the master mask or the slave mask that is different from the reference mask.

[0013] In the electrochemical reaction visualization device, the image processing unit may further include an overlap calculation unit that calculates an overlap of at least one of the lengths in the first direction and the second direction of the tracking ROIs from the difference between at least one of the sum of the lengths in a first direction and the sum of the lengths in a second direction perpendicular to the first direction of each tracking ROI included in the master mask or the slave mask that is used as a reference mask, and at least one of the sum of the lengths in the first direction and the sum of the lengths in the second direction of each tracking ROI included in the master mask or the slave mask that is different from the reference mask.

[0014] In the electrochemical reaction visualization device, the image processing unit may further include an annihilation area calculation unit that calculates the area of ​​the tracking ROIs of the master mask or the slave mask that are used as a reference mask, which have disappeared in the master mask or the slave mask where the corresponding tracking ROI is different from the reference mask.

[0015] The electrochemical reaction visualization device further includes a linear expansion coefficient calculation unit that calculates the linear expansion coefficient of at least one of a first direction of the tracking ROI in each charging state and a second direction perpendicular to the first direction, and the linear expansion coefficient calculation unit may calculate at least one of an expansion function that approximates the change in the linear expansion coefficient over time, and a contraction function that approximates the change in the linear expansion coefficient over time.

[0016] In the electrochemical reaction visualization device, the windowed cell may include a fixed point, the color image data may be captured so as to include the fixed point, and the image processing unit may further include a drift correction unit that tracks the fixed point in the plurality of color image data and corrects positional deviations of each color image data so that the fixed point is in the same position.

[0017] In the electrochemical reaction visualization device, the master extraction unit and the slave extraction unit may separate the active material portion in each tracking ROI from a portion other than the active material portion.

[0018] In the electrochemical reaction visualization device, when the slave extraction unit cannot track the position of the active material portion extracted by the master extraction unit, the master extraction unit may select the color image data of a charge state other than the fully charged state, extract a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as the active material portion, extract a range surrounding the active material portion as a tracking ROI, generate a quasi-master ROI including a plurality of the tracking ROIs, and generate a quasi-master mask from the generated quasi-master ROI in which the portion of the tracking ROI is a valid region and the portion other than the tracking ROI is an invalid region.

[0019] The electrochemical reaction visualization method according to the present disclosure is an electrochemical reaction visualization method for visualizing state changes during charging and discharging of a secondary battery, the method comprising: a windowed cell having a transparent window and accommodating the secondary battery containing an active material whose luminance increases in a fully charged state; a charge / discharge controller that controls charging and discharging so that the secondary battery goes through a plurality of charge states with different charge amounts during the charging and discharging; and a color confocal imaging unit that illuminates the secondary battery with illumination light through the transparent window and has an objective lens that transmits light reflected by the secondary battery, and acquires color image data of the secondary battery while changing the relative distance between the objective lens and the secondary battery. The method includes a data acquisition step of acquiring the color image data for each charge state of the secondary battery and charge / discharge data for each charge state; a linking step of matching the color image data and the charge / discharge data in chronological order; a master extraction step of selecting the color image data for the fully charged state, extracting a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as an active material portion, and extracting a range surrounding the active material portion as a tracking ROI; and a slave extraction step of tracking the position of the extracted active material portion in the color image data corresponding to each charge state, and extracting a range surrounding the tracked active material portion as the tracking ROI.

[0020] The electrochemical reaction visualization method may further include a color analysis step of converting the RGB luminance of the active material portion into a hue to analyze each state of charge.

[0021] In the electrochemical reaction visualization method, the master extraction step may generate a master ROI including a plurality of the tracking ROIs, and generate a master mask from the generated master ROI in which the tracking ROIs are defined as valid regions and the other portions are defined as invalid regions; and the slave extraction step may generate a slave ROI including a plurality of the tracking ROIs, and generate a slave mask from the generated slave ROI in which the tracking ROIs are defined as valid regions and the other portions are defined as invalid regions.

[0022] The electrochemical reaction visualization method may further include an overlap calculation step of calculating the overlap of the tracking ROIs from the difference between the sum of the areas of the tracking ROIs included in the master mask or the slave mask that is used as a reference mask and the sum of the areas of the tracking ROIs included in the master mask or the slave mask that is different from the reference mask.

[0023] The electrochemical reaction visualization method may further include an overlap calculation step of calculating an overlap of at least one of the lengths in the first direction and the second direction of the tracking ROI from the difference between at least one of the sum of the lengths in a first direction and the sum of the lengths in a second direction perpendicular to the first direction of the tracking ROI included in the master mask or the slave mask that is used as a reference mask, and at least one of the sum of the lengths in the first direction and the sum of the lengths in the second direction of the tracking ROI included in the master mask or the slave mask that is different from the reference mask.

[0024] The electrochemical reaction visualization method may further include a disappearance area calculation step of calculating the area of ​​the tracking ROIs of the master mask or the slave mask that is used as a reference mask, where the corresponding tracking ROI is different from the reference mask and that has disappeared in the master mask or the slave mask.

[0025] The electrochemical reaction visualization method further includes a linear expansion coefficient calculation step of calculating the linear expansion coefficient of at least one of a first direction of the tracking ROI in each charging state and a second direction perpendicular to the first direction, and the linear expansion coefficient calculation step may calculate at least one of an expansion function that approximates the change in the linear expansion coefficient over time, and a contraction function that approximates the change in the linear expansion coefficient over time.

[0026] In the electrochemical reaction visualization method, the windowed cell may include a fixed point, the color image data may be captured so as to include the fixed point, and the method may further include a drift correction step of tracking the fixed point in a plurality of pieces of color image data and correcting positional deviations of each piece of color image data so that the fixed point is at the same position.

[0027] In the electrochemical reaction visualization method, the master extraction step and the slave extraction step may separate the active material portion in each tracking ROI from a portion other than the active material portion.

[0028] The electrochemical reaction visualization method may further include a quasi-master extraction step of, when the position of the active material portion extracted in the master extraction step cannot be tracked in the slave extraction step, selecting the color image data of a charge state other than a fully charged state, extracting a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as the active material portion, extracting a range surrounding the active material portion as a tracking ROI, generating a quasi-master ROI including a plurality of the tracking ROIs, and generating a quasi-master mask from the generated quasi-master ROI in which the portion of the tracking ROI is a valid region and the portion other than the tracking ROI is an invalid region. [Effects of the Invention]

[0029] According to the present invention, it is possible to provide an electrochemical reaction visualization device and an electrochemical reaction visualization method that can easily distinguish between active materials and electrolytes and analyze changes in the state of a secondary battery during charging and discharging. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a configuration diagram illustrating an electrochemical reaction visualization device according to a first embodiment. [Figure 2] 2 is a diagram illustrating a windowed cell in the electrochemical reaction visualization device according to the first embodiment. FIG. [Figure 3]2 is a block diagram illustrating a signal processing unit in the electrochemical reaction visualization device according to the first embodiment. FIG. [Figure 4] 2 is a block diagram illustrating an image processing unit in the electrochemical reaction visualization device according to the first embodiment. FIG. [Figure 5A] FIG. 1 is a diagram illustrating an outline of an electrochemical reaction visualization method according to a first embodiment, and is a schematic diagram illustrating a mixed state of an active material and a solid electrolyte. [Figure 5B] FIG. 1 is a diagram illustrating an outline of an electrochemical reaction visualization method according to the first embodiment, and is an all-in-focus image illustrating confocal observation of an electrode of an all-solid-state battery before charging. [Figure 5C] FIG. 1 is a diagram illustrating an outline of an electrochemical reaction visualization method according to the first embodiment, and is an all-in-focus image illustrating confocal observation of a fully charged electrode of an all-solid-state battery. [Figure 6] 1 is a conceptual diagram illustrating tracking of an active material in the electrochemical reaction visualization method according to the first embodiment. FIG. [Figure 7A] FIG. 2 is a diagram illustrating a method for generating a tracking ROI in the electrochemical reaction visualization method according to the first embodiment, showing color image data in a fully charged state. [Figure 7B] FIG. 2 is a diagram illustrating a method for generating a tracking ROI in the electrochemical reaction visualization method according to the first embodiment, showing color image data in which active materials are identified by their hues. [Figure 7C] FIG. 2 is a diagram illustrating a method for generating a tracking ROI in the electrochemical reaction visualization method according to the first embodiment, showing extraction of the tracking ROI. [Figure 8] FIG. 2 is a diagram illustrating a tracking ROI in the electrochemical reaction visualization method according to the first embodiment. [Figure 9] FIG. 2 is a diagram illustrating a master mask in the electrochemical reaction visualization method according to the first embodiment. [Figure 10] 3A to 3C are diagrams illustrating a process of creating a slave mask from a master mask in the electrochemical reaction visualization method according to the first embodiment. [Figure 11]FIG. 1 is a flowchart illustrating an electrochemical reaction visualization method according to the first embodiment. [Figure 12A] FIG. 10 is a diagram illustrating an example of a designated area in a secondary battery in an electrochemical reaction visualization method according to a comparative example. [Figure 12B] 10 is a graph illustrating an example of an analysis result of an average score in an electrochemical reaction visualization method according to a comparative example, in which the horizontal axis represents time and the vertical axis represents the average score. [Figure 12C] FIG. 10 is a diagram illustrating an example of coloring of an extracted active material portion in an electrochemical reaction visualization method according to a comparative example. [Figure 13A] 3 is a diagram illustrating an example of a designated area in a secondary battery in the electrochemical reaction visualization method according to the first embodiment. FIG. [Figure 13B] 1 is a graph illustrating the analysis results of the average points in the electrochemical reaction visualization method according to the first embodiment, where the horizontal axis represents time and the vertical axis represents the average points. [Figure 13C] FIG. 3 is a diagram illustrating an example of coloring of an extracted active material portion in the electrochemical reaction visualization method according to the first embodiment. [Figure 14] 10 is a block diagram illustrating an image processing unit in the electrochemical reaction visualization device according to the second embodiment. FIG. [Figure 15] FIG. 10 is a flowchart illustrating an electrochemical reaction visualization method according to a second embodiment. [Figure 16A] FIG. 10 is a diagram illustrating a line image in the electrochemical reaction visualization device according to the second embodiment. [Figure 16B] FIG. 10 is a diagram illustrating a line image in the electrochemical reaction visualization device according to the second embodiment. [Figure 16C] FIG. 10 is a diagram illustrating a line image in the electrochemical reaction visualization device according to the second embodiment. [Figure 17A] FIG. 10 is a diagram illustrating a state in which tracking ROIs do not overlap in the electrochemical reaction visualization device according to the second embodiment. [Figure 17B] FIG. 10 is a diagram illustrating an example of a state in which tracking ROIs overlap in the electrochemical reaction visualization device according to the second embodiment. [Figure 18] FIG. 10 is a diagram illustrating an example of overlapping of tracking ROIs in the electrochemical reaction visualization device according to the second embodiment. [Figure 19] 10 is a graph illustrating an expansion function and a contraction function in the electrochemical reaction visualization device according to the second embodiment, where the horizontal axis represents time, the left vertical axis represents the expansion rate, and the right vertical axis represents voltage. [Figure 20A] FIG. 10 is a diagram illustrating an example of correction of analysis ROI coordinates using an expansion function in the electrochemical reaction visualization device according to the second embodiment. [Figure 20B] FIG. 10 is a diagram illustrating an example of correction of analysis ROI coordinates using an expansion function in the electrochemical reaction visualization device according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] The specific configuration of this embodiment will be described below with reference to the drawings. The following description shows a preferred embodiment of the present invention, and the scope of the present invention is not limited to the following embodiment. In the following description, parts with the same reference numerals indicate substantially the same content.

[0032] (Embodiment 1) An electrochemical reaction visualization device and an electrochemical reaction visualization method according to embodiment 1 will be described. First, the configuration of the electrochemical reaction visualization device will be described, followed by the electrochemical reaction visualization method.

[0033] [Configuration of electrochemical reaction visualization device] FIG. 1 is a configuration diagram illustrating an electrochemical reaction visualization device according to a first embodiment. As shown in FIG. 1, the electrochemical reaction visualization device 100 includes a windowed cell 10, a charge / discharge controller 20, a color confocal imaging unit 30, and a signal processing unit 50. The signal processing unit 50 includes an image processing unit 70. The electrochemical reaction visualization device 100 may also include an image data storage, a general-purpose information processing device, and the like in addition to the above. The electrochemical reaction visualization device 100 visualizes state changes during charging and discharging of a secondary battery 1. Below, the components of the electrochemical reaction visualization device 100, including the windowed cell, the charge / discharge controller, the color confocal imaging unit, the signal processing unit, and the image processing unit, are described.

[0034] <Windowed cell> The test sample to be image-analyzed is, for example, a secondary battery 1 such as a lithium-ion battery. The secondary battery 1 is placed in a windowed cell 10. The windowed cell 10 has a transparent window 19 and houses the secondary battery 1. The windowed cell 10 seals the secondary battery 1. The interior of the windowed cell 10 is filled with an inert gas such as argon gas. The windowed cell 10 holds the secondary battery 1 such as a lithium-ion battery in an inert gas atmosphere.

[0035] Fig. 2 is a diagram illustrating a windowed cell 10 in the electrochemical reaction visualization device 100 according to embodiment 1. As shown in Figs. 1 and 2, the windowed cell 10 is designed to enable observation of a cross section of the secondary battery 1. The windowed cell 10 has a windowed lid and a cell body.

[0036] First, a secondary battery 1 using an electrolyte will be described. The secondary battery 1 has a laminated structure in which a positive electrode current collector 2, a positive electrode active material layer 3, a separator 4, a negative electrode active material layer 5, and a negative electrode current collector 6 are stacked. The positive electrode current collector 2 and the positive electrode active material layer 3 are called the positive electrode, and the negative electrode active material layer 5 and the negative electrode current collector 6 are called the negative electrode. For example, rolled aluminum foil is used as the positive electrode current collector 2, and a lithium cobalt oxide (LiCoO2) layer is used as the positive electrode active material layer 3. For example, copper foil is used as the negative electrode current collector 6, and a graphite layer is used as the negative electrode active material layer 5. A separator 4 is disposed between the positive electrode and the negative electrode to insulate them from each other. The positive electrode and the negative electrode are filled with an electrolyte, which is an organic electrolyte prepared by dissolving a lithium salt such as LiPF6 in an organic solvent such as ethylene carbonate (EC).

[0037] The secondary battery 1 is fabricated by, for example, sandwiching the positive electrode, separator 4, and negative electrode between electrode holders in a dedicated alignment jig, and then cutting them with a blade. The electrode holder is then sealed in the cell body along with the electrolyte, and the electrode cross section is pressed against a transparent window 19 attached to the lid. In this manner, the secondary battery 1 is observed. The process up to closing the lid is performed in a glove box or dry room, but after sealing the lid, observations are performed in the atmosphere. Gas may be generated during charge / discharge experiments. This gas not only interferes with observations, but also creates a dry, partially electrolyte-free environment, which is a major obstacle. To avoid these obstacles, the dedicated windowed cell 10 has the function of evacuating the generated gas from the observation area.

[0038] When an all-solid-state battery is used as the secondary battery 1, impregnation with an electrolyte solution is not necessary. Furthermore, no separator is used. The secondary battery 1 is formed by pressing a solid electrolyte and an electrode (a mixture of a solid electrolyte and an active material). An observation end surface can be created by cutting the secondary battery 1. In this embodiment, the secondary battery 1 may be any battery that produces a difference in luminance between a fully charged state and a state other than a fully charged state. For example, the secondary battery 1 may be one that uses an electrolyte solution containing an active material whose luminance increases in a fully charged state, or may be an all-solid-state battery.

[0039] <Charge / discharge controller> As shown in Figure 1, the charge / discharge controller 20 controls the charging and discharging of the secondary battery 1 so that the secondary battery 1 goes through a plurality of charge states with different charge amounts during charging and discharging. The windowed cell 10 is provided with first and second connection terminals 10a and 10b, which are connected to the positive and negative electrodes of the secondary battery 1, respectively. The first connection terminal 10a is connected to the I 0+ The second connection terminal 10b is connected to the I terminal of the charge / discharge controller 20. 0- It is connected to the terminal.

[0040] As a method for controlling charging and discharging, for example, charging can be performed by a constant current constant voltage method (CVCC). That is, at the start of charging, a constant current is supplied to the secondary battery 1 to charge it, and after it reaches full charge, charging is performed at a constant voltage. Discharge control can also be performed by constant current control. The first and second connection terminals 10a and 10b are connected to the V + and V - The charge / discharge voltage (battery voltage) is detected as time-series data by a voltage detection means connected to the terminals and provided in the charge / discharge controller 20. Furthermore, the charge / discharge controller 20 has a current detection means for detecting the current flowing through the secondary battery 1, and outputs the value of the current flowing through the secondary battery 1 as time-series data. The detected charge / discharge voltage and charge / discharge current are output to the signal processing unit 50 as charge / discharge data.

[0041] <Color confocal imaging unit> The color confocal imaging unit 30 includes an illumination light source 31, a beam splitter 32, a two-dimensional scanner 33, an objective lens 34, a motor 35, a distance sensor 36, and an image acquisition unit 37. The illumination light source 31 is a white light source that generates white light, such as a mercury lamp or a white laser.

[0042] The white illumination beam emitted from the illumination light source 31 is incident on the beam splitter 32. The beam splitter 32 functions to separate the illumination beam directed from the illumination light source 31 toward the secondary battery 1 from the beam reflected by the secondary battery 1. The beam splitter 32 is, for example, a half mirror.

[0043] The illumination beam transmitted through the beam splitter 32 enters the two-dimensional scanner 33, undergoes two-dimensional scanning in the X and Y directions, and then enters the objective lens 34. The illumination beam is converted into a focused beam by the objective lens 34 and enters the windowed cell 10. In this way, the objective lens 34 illuminates the secondary battery 1 with illumination light through the transparent window 19.

[0044] A motor 35 is connected to the objective lens 34, allowing it to move continuously in the optical axis direction at a predetermined speed. Therefore, the focal point of the illumination beam moves continuously along the optical axis direction during two-dimensional scanning. The position of the objective lens 34 in the optical axis direction is detected by a distance sensor 36, and is supplied to a signal processing unit 50 as relative distance information between the objective lens 34 and the surface of the secondary battery 1. It is preferable to use an objective lens 34 with plate thickness correction.

[0045] The illumination beam passes through a transparent window 19 provided in the windowed cell 10 and is incident on the secondary battery 1 during charging and discharging. In this embodiment, color image data of the cross section of the secondary battery 1 is captured. Therefore, the secondary battery 1 is positioned so that its cross section faces the transparent window 19. The illumination beam is two-dimensionally scanned by a two-dimensional scanner, so that the cross section of the secondary battery 1 during charging and discharging is two-dimensionally scanned by the focused illumination beam. Furthermore, because the illumination beam scans the cross section two-dimensionally while the objective lens 34 moves in the optical axis direction, a two-dimensional image (all-in-focus image) in focus over the entire field of view is captured. Therefore, if an uneven surface is exposed on the cross section of the secondary battery 1, an image in focus (in-focus) of the entire uneven surface is captured.

[0046] The reflected beam reflected by the cross section of the secondary battery 1 during charging and discharging passes through the transparent window 19 and is collected by the objective lens 34. Therefore, the objective lens 34 transmits the light reflected by the secondary battery 1 from the illumination light. The reflected light that passes through the objective lens 34 passes through the two-dimensional scanner 33 and enters the beam splitter 32. It is then reflected by the beam splitter 32 and enters the image acquisition unit 37.

[0047] The image acquisition unit 37 includes an imaging lens system, a color separation optical system that separates the incident reflected beam into RGB color component lights, and three image sensors that receive the RGB color component lights, respectively. The color separation optical system includes, for example, a prism. The image sensors include, for example, a CDD, a line sensor, etc.

[0048] In this way, the color confocal imaging section 30 illuminates the secondary battery 1 with illumination light through the transparent window 19, and has an objective lens 34 that transmits light reflected from the illumination light by the secondary battery 1. The color confocal imaging section 30 acquires color image data of the secondary battery 1 while changing the relative distance between the objective lens 34 and the secondary battery 1. Therefore, the color confocal imaging section 30 constitutes a color confocal optical system, and a high-resolution color confocal image is captured.

[0049] In one imaging operation, multiple color image data are acquired while the objective lens 34 is moved a predetermined distance in the optical axis direction. The time required to acquire one color image data set is, for example, 30 seconds. The objective lens 34 is moved a predetermined distance in 30 seconds, and multiple color image data sets are acquired during that time. The time interval between imaging operations can be, for example, one minute. Therefore, color image data is acquired at one-minute intervals. The RGB color image data output from the three imaging elements is supplied to the signal processing unit 50 as time-series data, and after signal processing, becomes color image data of the integrated secondary battery 1. The color confocal imaging unit 30 has the following features.

[0050] [1] The color confocal imaging unit 30 detects only the reflected light from the focused position on the observation surface of the secondary battery 1. This makes it possible to eliminate unnecessary scattered light from the transparent window 19, even if it is present in front of the observation surface, unlike a typical optical microscope. Furthermore, even if the observation surface is submerged in liquid, unnecessary scattered light from the liquid can be eliminated, allowing the observation surface to be clearly observed.

[0051] [2] The color confocal imaging unit 30 can obtain an "all-in-focus image" with an infinite depth of focus by synthesizing the moment when each pixel is brightest while scanning the secondary battery 1 in the focal direction. The color confocal imaging unit 30 can focus on all parts of the three-dimensional LiB electrode, which is often composed of particles several micrometers in size, and can measure not only the horizontal dimensional changes of the active material particles but also the positional changes in the depth direction.

[0052] In the case of operando observation, data is acquired by using the color confocal imaging unit 30 while charging and discharging are performed by a charge / discharge program. With this, an image is captured every minute, for example, and a color observation image is saved.

[0053] <Signal processing section> An input device 51 such as a keyboard and a monitor 52 are connected to the signal processing unit 50. An operator can input designation information that designates the analysis data to be output via the input device 51. The designated analysis data is displayed on the monitor 52.

[0054] FIG. 3 is a block diagram illustrating the signal processing unit 50 in the electrochemical reaction visualization device 100 according to the first embodiment. As shown in FIG. 3, the signal processing unit 50 has a clock device 53 used to temporally link image data and charge / discharge data. The signal processing unit 50 uses a clock signal output from the clock device 53 as a common clock signal to link the color image data and the charge / discharge data. That is, the start of charge / discharge and the elapsed time after the start of charge are measured based on the clock signal output from the clock device 53. The acquired color image data and charge / discharge data are stored in memory as a pair with the clock signal output from the clock device 53. Therefore, the clock device 53 and the memory function as a linking means for linking the image data and the charge / discharge data.

[0055] The RGB color image signals are supplied to the omnifocal image forming means 54. The omnifocal image forming means 54 detects the maximum luminance value for each pixel in multiple color confocal images captured while moving the objective lens 34 in the optical axis direction, and forms a two-dimensional image composed of the maximum luminance values ​​as the omnifocal image. That is, by moving the objective lens 34 in the optical axis direction, the focal point of the illumination beam is displaced in the optical axis direction. When the focal point of the illumination beam is positioned on the surface of the secondary battery 1, the maximum luminance value is output from the image sensor. Therefore, by capturing multiple two-dimensional images while moving the objective lens 34 in the optical axis direction and detecting the maximum luminance value for each pixel, an omnifocal image in focus over the entire imaging area can be formed. Therefore, if the cross section of the active material layer of the secondary battery 1 has irregularities, the omnifocal image forming means 54 forms a color image in focus on the irregular surface. The omnifocal image is formed at intervals of, for example, one minute.

[0056] The color all-in-focus image signal is supplied to a first memory 55. Clock information output from a clock device 53 is also input to the first memory 55. The first memory 55 sequentially stores pairs of time-series color all-in-focus images and clock information.

[0057] The relative distance information (Z-axis information) output from the distance sensor 36 is supplied to the three-dimensional image forming means 56. The three-dimensional image forming means 56 forms a three-dimensional image of the surface of the secondary battery 1 using the relative distance information at the time when the maximum brightness value is detected for each pixel in the omnifocal image forming means 54. That is, when the maximum brightness value is output from the imaging element, the focal point of the illumination beam is located on the surface of the secondary battery 1. Therefore, a three-dimensional image of the observation surface of the secondary battery 1 can be formed using position information or distance information in the optical axis direction at the time when the maximum brightness value is output. The three-dimensional images are formed continuously at one-minute time intervals, similar to the formation of the omnifocal images.

[0058] The formed 3D image signals are sequentially supplied to a second memory 57. Clock information supplied from the clock device 53 is also input to the second memory 57. The second memory 57 stores the input 3D image signals and clock signals as pairs.

[0059] The time-series charge / discharge data output from the charge / discharge controller 20 is supplied to a third memory 58. A clock signal output from the clock device 53 is also supplied to the third memory 58. The input charge / discharge data, i.e., the charge / discharge voltage and charge / discharge current, and clock information are each stored as a pair. The charge / discharge data is supplied to an SOC calculation means 59, which determines the state of charge (SOC) after the start of charging from the charge / discharge current. The state of charge is data that indicates the amount of electricity stored in the secondary battery 1. The integrated amount of electricity is calculated from the charge / discharge data, and the amount of electricity normalized with respect to the fully charged state, with full charge being 100%, is shown. The calculated state of charge is stored in a fourth memory 60 together with the clock information. As a result, the state of charge linked to the image data is stored in the fourth memory 60.

[0060] The omnifocal color image data stored in the first memory 55 is supplied to the image processing unit 70. The color image data is associated with a clock signal. Furthermore, the charge / discharge data stored in the third memory 58 is supplied to the image processing unit 70 via the fourth memory 60 together with the charge state. The charge / discharge data and the charge state are associated with the clock signal. The image processing unit 70 acquires color image data for each charge state of the secondary battery 1 and charge / discharge data for each charge state. The output means 61 outputs various data to the monitor 52.

[0061] <Image processing unit> 4 is a block diagram illustrating the image processing unit 70 in the electrochemical reaction visualization device 100 according to embodiment 1. As shown in FIG. 4, the image processing unit 70 includes an acquisition unit 71, a link unit 72, a master extraction unit 73, a slave extraction unit 74, and a color analysis unit 75.

[0062] The acquisition unit 71 acquires color image data for each charge state of the secondary battery and charge / discharge data for each charge state. The linking unit 72 associates the color image data with the charge / discharge data in chronological order. Specifically, the linking unit 72 links a clock signal associated with the color image data with a clock signal associated with the charge / discharge data, thereby associating them in chronological order. The master extraction unit 73 extracts a master ROI (described below) and generates a master mask. The slave extraction unit 74 extracts a slave ROI (described below) and generates a slave mask. Note that a single extraction unit that combines the master extraction unit 73 and the slave extraction unit 74 may have the functions of both the master extraction unit 73 and the slave extraction unit 74. The color analysis unit 75 analyzes the color of the active material portion in the color image data.

[0063] The signal processing unit 50 including the image processing unit 70, or simply the image processing unit 70, may be, for example, an information processing device such as a server device or a personal computer. These devices each have a control unit, a communication unit, a storage unit, and an interface unit, which are not shown. The control unit, the communication unit, the storage unit, and the interface unit function as a control means, a communication means, a storage means, and an interface means, respectively.

[0064] The control unit includes a processor such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), ECU (Electronic Control Unit), FPGA (Field-Programmable Gate Array), or ASIC (Application Specific Integrated Circuit). The control unit functions as a computing device that performs control processing, arithmetic processing, etc. The control unit also controls the operation of the communication unit, storage unit, interface unit, and each component that executes the function of each device.

[0065] Each component of each device can be realized, for example, by executing a program under the control of a control unit. More specifically, each component, such as the acquisition unit 71, link unit 72, master extraction unit 73, slave extraction unit 74, and color analysis unit 75, can be realized by the control unit executing a program stored in a storage unit. Alternatively, each component may be realized by recording the necessary program on an arbitrary non-volatile recording medium and installing it as needed. Furthermore, each component is not limited to being realized by software using a program, but may also be realized by any combination of hardware, firmware, and software.

[0066] The communication unit performs communication necessary for each device to perform information processing. The storage unit is, for example, a ROM (Read Only Memory) or a RAM (Random Access Memory). The storage unit has a function for storing control programs and calculation programs executed by the control unit. The storage unit also has a function for temporarily storing processing data, etc.

[0067] The interface unit is, for example, a user interface. The interface unit is connected to an input device 51 such as a keyboard, touch panel, or mouse, and a monitor 52 such as a display or speaker. The interface unit accepts data input operations by a user (such as an operator), and outputs information to the user. Each function of the image processing unit 70 will be described in the electrochemical reaction visualization method below.

[0068] [Electrochemical reaction visualization method] Next, we will explain the electrochemical reaction visualization method in the following order: <Overview>, <Creating a tracking ROI>, <Creating a master mask>, <Creating a slave mask>, <Tracking method>, <Flowchart of the procedure from data reading to tracking analysis>, and <Color analysis>.

[0069] <Summary> 5A to 5C are diagrams illustrating an outline of the electrochemical reaction visualization method according to embodiment 1. Fig. 5A is a schematic diagram of a mixed state of an active material and a solid electrolyte, Fig. 5B is an all-in-focus image illustrating confocal observation of an electrode of an all-solid-state battery before charging, and Fig. 5C is an all-in-focus image illustrating confocal observation of an electrode of a fully charged all-solid-state battery.

[0070] As shown in FIG. 5A, the electrochemical reaction visualization method of this embodiment is based on the premise of distinguishing between an active material A, which changes color depending on the state of charge, and a material B, which does not change color. For example, the observed color of graphite, a typical active material for all-solid-state batteries, changes stepwise (gray → blue → red → gold) depending on the state of charge. This change is thought to occur because lithium intercalates between the layers of graphite layer crystals, changing the electronic state of the graphite and causing a change in the reflection spectrum. On the other hand, a solid electrolyte (referred to as SE) does not change color with charging and discharging, unlike graphite. Therefore, in the uncharged state, the brightness and color of the active material are similar to the color of the SE, making them difficult to distinguish from the image.

[0071] As shown in FIG. 5B, in the uncharged state before charging, the active material A, which changes color, and the material B, which does not change color, are difficult to distinguish between because their colors are similar. On the other hand, as shown in FIG. 5C, in the fully charged state, the color of the active material A changes to gold. This makes it possible to distinguish between the active material A and the material B. Therefore, in this embodiment, only the active material A, which changes color depending on the charge state, is extracted, and the color change is quantified to observe the relationship between the charge / discharge state (charge / discharge voltage) corresponding to the charge / discharge time and the color change.

[0072] 6 is a conceptual diagram illustrating tracking of an active material in the electrochemical reaction visualization method according to embodiment 1. As shown in FIG. 6, in the initial state (a), which is an uncharged state, it is difficult to distinguish between active material A (e.g., graphite) that changes color when charged and material B that does not change color. In the state (b) over time during charging, the color of active material A that changes color when charged changes. Then, in the fully charged state (c), active material A changes to gold. Therefore, active material A can be distinguished from material B that does not change color.

[0073] First, to distinguish between active material A, which changes color when charged, and material B, which does not change color, active material A is extracted using an image containing active material A that has turned gold in a fully charged state (c) where the state of charge (SOC) is 100%. Then, the area surrounding the extracted active material A is set as the tracking ROI.

[0074] Specifically, the master extraction unit 73 selects color image data of a fully charged state. The master extraction unit 73 extracts, as an active material portion, a portion of the selected color image data whose brightness is equal to or greater than a predetermined threshold. The master extraction unit 73 then extracts a range surrounding the active material portion as a tracking ROI. The master extraction unit 73 also sets an area including multiple tracking ROIs as a master ROI. The master extraction unit 73 generates a master mask from the master ROI.

[0075] Next, the tracking ROI, which is the range used to extract active material A, continues to track active material A by going back in time to the initial state (a) and the state over time (b), or by going forward in time to the state over time (d) and the final state (e).

[0076] Specifically, the slave extraction unit 74 tracks the position of the extracted active material portion in the color image data corresponding to each state of charge. The slave extraction unit 74 extracts an area surrounding the tracked active material portion as a tracking ROI. The slave extraction unit 74 also sets an area including multiple tracking ROIs as a slave ROI. The slave extraction unit 74 generates a slave mask from the slave ROI.

[0077] <Generating tracking ROI> Next, the generation of tracking ROIs will be described in detail. Figures 7A to 7C are diagrams illustrating a method for generating tracking ROIs in the electrochemical reaction visualization method according to embodiment 1. Figure 7A shows color image data in a fully charged state (SOC 100%), Figure 7B shows color image data in which active materials are identified by hue, and Figure 7C shows extraction of tracking ROIs.

[0078] As shown in FIG. 7A, when extracting a tracking ROI, first, color image data for a fully charged state (SOC 100%) where the state of charge is 100% is selected. Next, as shown in FIG. 7B, the color-changed active material portion AP is colored. The coloring will be explained in the Color Analysis section. Then, as shown in FIG. 7C, the colored active material portion AP is extracted. The extracted active material portion is enclosed in a square on the image. The enclosed square is called a tracking ROI (also called a T-ROI). Note that to avoid cluttering the diagram, only some active material portions AP and tracking ROIs are labeled, and some active material portions AP and tracking ROIs are omitted. In this way, the tracking ROI is extracted. When only the tracking ROIs extracted from the color image data are extracted, each tracking ROI is set to encompass the maximum length and width (X and Y) of the extracted active material portion.

[0079] FIG. 8 is a diagram illustrating a tracking ROI in the electrochemical reaction visualization method according to the first embodiment. As shown in FIG. 8, for example, the color image data is assumed to be an XY plane. The XY coordinates of the upper left corner of the rectangular frame of the tracking ROI are set as the coordinates of that tracking ROI. Note that the XY coordinates are not limited to the upper left corner of the rectangular frame of the tracking ROI, but may also be the upper right corner, lower left corner, lower right corner, center, etc. Basically, the size and shape of each tracking ROI set here are unchanged. However, the tracking ROI size may be changed when applying the tracking ROI to an image other than an SOC of 100% or when recreating it midway.

[0080] <Creating a master mask> Next, a master mask is created for the collection of multiple tracking ROIs. First, the entire area from which the tracking ROIs are extracted is called the master ROI or M-ROI. Therefore, the master ROI contains multiple tracking ROIs. Within the master ROI, the area inside the tracking ROIs is set as the "valid area," and the rest is set as the "invalid area." For example, the "valid area" is represented as "1" and is shown in "white," and the "invalid area" is represented as "0" and is shown in "black."

[0081] FIG. 9 is a diagram illustrating a master mask in the electrochemical reaction visualization method according to the first embodiment. As shown in FIG. 9, the master extraction unit 73 generates a master mask from the generated master ROI, with the tracking ROI portion as the valid region and the region other than the tracking ROI as the invalid region. The master mask is also called an M-Mask. The master mask refers to a binary mask. By performing a logical AND between the image to be analyzed and the master mask, it is possible to narrow down the analysis target to only the "valid region."

[0082] <Create a slave mask> 10 is a diagram illustrating a process of creating a slave mask from a master mask in the electrochemical reaction visualization method according to embodiment 1. As shown in FIG. 10, the master extraction unit 73 selects color image data in a fully charged state (SOC 100%) and generates a master ROI (M-ROI) and a master mask (M-Mask). For ease of explanation, the master mask and the slave mask do not have to be displayed as binary masks on the monitor 52 as shown in FIG. 10.

[0083] A mask generated from color image data other than the fully charged state is called a slave mask (S-Mask). The slave mask is generated as follows: The slave extraction unit 74 sets the tracking ROI in the master mask as the initial condition. Then, the slave extraction unit 74 generates multiple slave ROIs (S-ROIs) by tracking each tracking ROI according to changes in the charging state. Each slave ROI includes multiple tracking ROIs.

[0084] Then, the slave extraction unit 74 generates a slave mask from the generated slave ROI, with the tracking ROI portion as the valid region and the portion outside the tracking ROI as the invalid region. In other words, what is generated based on this reset tracking ROI is the "slave mask."

[0085] <Tracking method> The tracking may be performed using an object tracking method. The area surrounding the active material portion PA (tracking ROI) is captured by tracing back in time to the uncharged state (SOC 0%). Alternatively, the area surrounding the active material portion PA (tracking ROI) is captured by tracing forward in time to the end-of-discharge state (SOC 0%). Specific object tracking algorithms include methods provided by OPEN-CV and the like (e.g., KCF, Kernelized Correlation Filters). A slave mask may be generated for all color image data stored in a folder such as memory in chronological order.

[0086] <Flowchart of the procedure from data loading to tracking analysis> Next, the procedure from data reading to tracking analysis will be described for an electrochemical reaction visualization method for visualizing state changes during charging and discharging of a secondary battery. FIG. 11 is a flowchart illustrating an example of an electrochemical reaction visualization method according to the first embodiment. As shown in step S10 of FIG. 11, color image data is read. Specifically, the acquisition unit 71 of the image processing unit 70 reads color image data captured by the color confocal imaging unit 30. The color image data captured of the secondary battery 1 is stored in, for example, the first memory 55. The acquisition unit 71 reads the color image data from the first memory 55.

[0087] Furthermore, as shown in step S20, charge / discharge data such as voltage and current are read. Specifically, the acquisition unit 71 reads charge / discharge data such as voltage and current when capturing color image data of the secondary battery 1. The charge / discharge data is stored in, for example, the fourth memory 60. The acquisition unit 71 reads the charge / discharge data from the fourth memory 60. Note that the order of steps S10 and S20 is not limited to this, and step S10 may be performed after step S20, or steps S10 and S20 may be performed in parallel. In other words, it is sufficient for the acquisition unit 71 to be able to acquire color image data of each charge state of the secondary battery 1 and charge / discharge data of each charge state from the electrochemical reaction visualization device 100.

[0088] Next, as shown in step S30, the color image data and the charge / discharge data are linked. Specifically, the linking unit 72 synchronizes the data using time as a key, and associates the acquired color image data and charge / discharge data in chronological order.

[0089] Next, as shown in step S40, tracking analysis is performed. Specifically, the image processing unit 70 creates a master mask and performs tracking, as described above. Note that color analysis, which will be described later, may also be performed.

[0090] First, as shown in step S41, a master mask is generated. The master extraction unit 73 selects color image data of the fully charged state and extracts, from the selected color image data, portions whose brightness is equal to or greater than a predetermined threshold as active material portions. The master extraction unit 73 then extracts a range surrounding the extracted active material portion as a tracking ROI. The master extraction unit 73 also generates a master ROI including multiple tracking ROIs, and generates a master mask from the generated master ROI in which the tracking ROI portions are defined as valid regions and portions other than the tracking ROIs are defined as invalid regions. In this way, the master extraction unit 73 generates the master ROI and master mask.

[0091] Next, tracking is performed as shown in step S42. The slave extraction unit 74 tracks the position of the extracted active material portion in the color image data corresponding to each state of charge. The slave extraction unit 74 extracts an area surrounding the tracked active material portion as a tracking ROI. The slave extraction unit 74 then generates a slave ROI including multiple tracking ROIs, and generates a slave mask from the generated slave ROI, in which the tracking ROI portion is a valid region and the portion other than the tracking ROI is an invalid region. In the tracking analysis, color analysis may be performed as shown in step S43. The color analysis is described below.

[0092] <Color analysis> The charge / discharge uniformity of the secondary battery 1 is an important factor that determines the performance of the secondary battery 1. The electrochemical reaction visualization device 100 of this embodiment can visualize the reaction distribution of an electrode containing an active material (for example, a graphite negative electrode in a composite electrode) during charge / discharge. For example, the amount of Li in graphite, which is an active material, correlates with color change (blue → red → gold). Therefore, the RGB brightness can be converted into hue (also called H) using the following equation (1), and the color change can be quantified.

[0093] Therefore, color analysis is performed as shown in step S43 of Fig. 11. Specifically, color analysis unit 75 analyzes each state of charge by converting the RGB luminance of the active material portion into hue. The spatial average values ​​of the RGB components extracted from the color image data are defined as R, G, and B, respectively.

[0094]

number

[0095] Furthermore, this Hue is divided into the graphite color change range of blue: -120 degrees to red: 0 degrees to yellow 60 degrees. Then, the following average score is calculated.

[0096] Gold: 100 points Red: 50 points Blue: 30 points Average score = "Gold" x 100 points + "Red" x 50 points + "Blue" x 30 points

[0097] In this way, by calculating the average point, we can obtain the time change of the spatial distribution. For example, the thickness direction is the stacking direction of the current collecting band, negative electrode (graphite), and SE. By specifying two areas separated in the thickness direction and calculating the average point of each area, we can quantify the reaction distribution in the thickness direction of the secondary battery 1.

[0098] Before describing this embodiment, a comparative example will be described. Fig. 12A is a diagram illustrating a designated area in a secondary battery 1 in an electrochemical reaction visualization method according to a comparative example. Fig. 12B is a graph illustrating an analysis result of an average point in an electrochemical reaction visualization method according to a comparative example, where the horizontal axis represents time and the vertical axis represents the average point. Fig. 12C is a diagram illustrating an example of coloring of an extracted active material portion in an electrochemical reaction visualization method according to a comparative example.

[0099] As shown in FIG. 12A, the areas for calculating the average score are, for example, two areas on the negative electrode: a separator-side analysis area (Area 1) and a current-collector-side analysis area (Area 2). Each area is called an "analysis ROI." The separator-side analysis area (Area 1) and the current-collector-side analysis area (Area 2) are separated in the thickness direction. As shown in FIG. 12B, in the comparative electrochemical reaction visualization method, the average score is lower than the expected average score. Furthermore, the reaction time difference is longer than expected. This is because, as shown in FIG. 12C, the comparative electrochemical reaction visualization method cannot distinguish between active materials such as graphite and SEs, so the active materials and SEs are analyzed together. Therefore, the state of charge (SOC) is recognized as 30%.

[0100] Next, this embodiment will be described. Fig. 13A is a diagram illustrating a designated area in a secondary battery 1 in the electrochemical reaction visualization method according to embodiment 1. Fig. 13B is a graph illustrating an analysis result of the average point in the electrochemical reaction visualization method according to embodiment 1, where the horizontal axis represents time and the vertical axis represents the average point. Fig. 13C is a diagram illustrating the coloring of an extracted active material portion in the electrochemical reaction visualization method according to embodiment 1.

[0101] As shown in FIG. 13A, in this embodiment, as in the comparative example, the areas for calculating the average score are, for example, two areas on the negative electrode: the separator-side analysis area (Area 1) and the current-collector-side analysis area (Area 2). As shown in FIG. 13B, in the electrochemical reaction visualization method of this embodiment, the average score is the expected average score. Furthermore, the reaction time difference is as expected. As shown in FIG. 13C, the electrochemical reaction visualization method of this embodiment can extract only the active material portion of graphite. Therefore, color analysis can be performed on the active material portion without being affected by SE. This allows for analysis of only the graphite in an all-solid-state battery, and the expected score can be obtained. The reaction time difference can also be quantified.

[0102] Next, the effects of this embodiment will be described. The electrochemical reaction visualization device 100 of this embodiment extracts the active material after the secondary battery 1 is fully charged. Therefore, it is possible to clearly separate the active material from non-active materials. In addition, the area surrounding the extracted active material is extracted as a tracking ROI, and tracking is performed. Therefore, by tracking the active material in each state of charge, it is possible to distinguish the active material from the electrolyte. In this way, this embodiment can easily distinguish between the active material and the electrolyte in each state of charge, thereby analyzing the state of charge of the secondary battery 1.

[0103] In conventional secondary batteries 1 using transparent electrolytes, such as lithium-ion batteries, it has been easy to distinguish between the electrolyte and the active material when observing the charge / discharge state using a color confocal microscope. However, in secondary batteries 1 using electrolytes that are difficult to distinguish from the active material by brightness or color in the uncharged state, such as all-solid-state batteries, it is difficult to perform operando observation of the electrochemical reaction inside the battery. In contrast, in this embodiment, active materials that change color or brightness depending on the charge state are identified. Then, by tracking each charge state, the charge state distribution of the all-solid-state battery can be visualized.

[0104] Furthermore, in the present embodiment, even in the case of an all-solid-state battery, the reaction distribution and reaction time of the active material can be detected with high accuracy by color analysis.

[0105] (Embodiment 2) Next, an electrochemical reaction visualization device and an electrochemical reaction visualization method according to a second embodiment will be described. This embodiment relates to an electrode evaluation method using tracking. FIG. 14 is a block diagram illustrating an image processing unit 70 in the electrochemical reaction visualization device 100 according to the second embodiment. As shown in FIG. 14, the image processing unit 70 has a drift correction unit 76, an overlap calculation unit 77, a disappearance area calculation unit 78, and a linear expansion coefficient calculation unit 79. The image processing unit 70 may have at least one of the drift correction unit 76, the overlap calculation unit 77, the disappearance area calculation unit 78, and the linear expansion coefficient calculation unit 79.

[0106] 15 is a flowchart illustrating an electrochemical reaction visualization method according to embodiment 2. Compared to the electrochemical reaction visualization method according to embodiment 1, the electrochemical reaction visualization method according to this embodiment includes drift correction by tracking (step S31), line image creation (steps S32 and S37), drift correction (step S33), quasi-master mask creation by re-tracking (step S34), active material degradation evaluation 1 (step S35), active material degradation evaluation 2 (step S36), and expansion function correction of analysis ROI coordinates (step S38).

[0107] The following sections, "Drift correction," "Line image creation," "Active material degradation evaluation 1," "Active material degradation evaluation 2," "Correction by linear expansion function," "Separation of active material and solid electrolyte," and "Re-tracking," will explain each of the above-mentioned configurations and steps.

[0108] [Drift correction] To effectively perform tracking analysis of the active material, it is necessary to minimize the positional deviation (drift) in the X and Y directions on the color image data of the secondary battery 1 caused by the optical system. Therefore, as shown in steps S31 to S33, drift correction by tracking and / or drift correction by creating a line image is performed. Drift correction can be performed by first tracking a fixed point (a marker for part of the holder) other than the active material within the field of view in the time-series color image data and calculating drift correction values ​​(ΔX, ΔY) such that the fixed point has the same X and Y coordinates for all color image data, or by measuring the positional change on the line of the fixed point from a line image, as described below. Then, as shown in step S33, drift correction is performed by applying these drift correction values ​​to all frames.

[0109] Specifically, the windowed cell 10 includes a fixed point. The color image data is captured so as to include the fixed point. The drift correction unit 76 tracks the fixed point in the multiple color image data and corrects the positional deviation of each color image data so that the fixed point is located at the same position.

[0110] This correction can remove sudden blurring of color image data. When calculating the coordinate correction value, it is important to perform sub-pixel processing using bicubic interpolation or the like to eliminate jerky effects caused by pixel size quantization.

[0111] [Create line image] A line image is created as shown in steps S32 and S37. FIGS. 16A to 16C are diagrams illustrating a line image in the electrochemical reaction visualization device according to the second embodiment. The line image is an image in which color image data obtained in time series at a predetermined position (e.g., in the thickness direction between the positive and negative electrodes of an all-solid-state secondary battery) is arranged in time series. In FIGS. 16B and 16C, the horizontal axis indicates the passage of time, and the vertical axis indicates, for example, the position of a pixel on a measurement line LM, which is the thickness direction. For example, as shown in FIG. 16A, a measurement line LM passing through a fixed point NP is set, and the color image data for the measurement line LM are arranged in time series to obtain a line image as shown in FIG. 16B. This line image can be used for drift correction by analyzing the trajectory of the fixed point NP, or for correcting a linear expansion function or contraction function, which will be described later (e.g., FIG. 16C).

[0112] [Active material degradation evaluation 1] Fig. 17A is a diagram illustrating a state in which there is no overlap of tracking ROIs in the electrochemical reaction visualization device 100 according to embodiment 2. Fig. 17B is a diagram illustrating a state in which there is overlap of tracking ROIs in the electrochemical reaction visualization device 100 according to embodiment 2.

[0113] As shown in Figure 17A, the area of ​​each tracking ROI of the active material remains constant throughout all color image data, so this total area is defined as ΣA. As shown in Figure 17B, tracking ROIs within the same color image data may overlap when the active material approaches or moves. In this case, the overlapping areas are not analyzed as duplicates in the color evaluation. Furthermore, the total area including this overlap is defined as ΣS. For example, the total overlapping area C can be written as in equation (2).

[0114]

number

[0115] In this way, when calculating the overlap, the master mask or slave mask used to calculate ΣA is set as the reference mask. The reference mask may be any master mask or slave mask as long as it can calculate ΣA. A quasi-master mask, which will be described later, may also be used as the reference mask. In step S35, the overlap calculation unit 77 calculates the overlap of the tracking ROIs from, for example, the difference between the sum of the areas of the tracking ROIs in the master mask or slave mask set as the reference mask and the sum of the areas of the tracking ROIs included in the master mask or slave mask different from the reference mask. If there is no overlap between the tracking ROIs, then C=0. Here, the parameter Φ is defined as in equation (3).

[0116]

number

[0117] If we consider that particles of active material pushing against each other during charging and discharging can lead to particle collapse and deterioration, then the change in Φ can be used as a parameter to evaluate electrode deterioration. This is a simple method that does not require color analysis, and can be applied to the evaluation of active materials other than graphite, which do not show much color change.

[0118] FIG. 18 is a diagram illustrating an example of overlap of tracking ROIs in the electrochemical reaction visualization device 100 according to the second embodiment. As shown in FIG. 18, by calculating the overlap not as an area but as the sum of the overlap lengths Lx in the X direction (for example, the first direction) and the sum of the overlap lengths Ly in the Y direction (for example, the second direction), it is possible to evaluate the directionality of deformation and movement of the active material in the secondary battery 1. The ratio of the non-overlapping length in the X direction to the total length of the tracking ROI in the X direction and the ratio of the non-overlapping length in the Y direction to the total length of the tracking ROI in the Y direction are defined by equations (4) and (5), respectively. The total length of the tracking ROI in the X direction and the total length of the tracking ROI in the Y direction are defined by ΣL RX and ΣL RY Let's say.

[0119]

number

number

[0120] Here, when calculating the overlap, ΣL RX and ΣL RY The master mask or slave mask used to calculate ΣL is used as the reference mask. RX and ΣL RY Any master mask or slave mask may be used as long as it can calculate the overlap area. A quasi-master mask, described later, may also be used as the reference mask. In step S35, the overlap calculation unit 77 calculates the overlap area of ​​at least one of the X- and Y-direction lengths of the tracking ROIs included in the master mask or slave mask serving as the reference mask, based on the difference between the sum of the X- and Y-direction lengths of each tracking ROI included in a master mask or slave mask different from the reference mask and the sum of the X- and Y-direction lengths of each tracking ROI included in the master mask or slave mask different from the reference mask. In active material degradation evaluation 1, the overlap calculation unit 77 evaluates the degradation of the active material by calculating at least one of the overlap area and overlap length of the tracking ROIs.

[0121] [Active material degradation evaluation 2] When tracking an active material, if the active material cannot be captured due to breakage, collapse, etc., the attribute of that tracking ROI is set to "Lost." The total area of ​​the tracking ROIs with the Lost attribute is ΣL, and the parameter χ is defined as in equation (6).

[0122]

number

[0123] Here, the master mask or slave mask used to calculate ΣA is used as the reference mask. The reference mask may be any master mask or slave mask as long as it can calculate ΣA. A quasi-master mask, described later, may also be used as the reference mask. The vanishing area calculation unit 78 calculates the area of ​​vanished tracking ROIs in the master mask or slave mask used as the reference mask, whose corresponding tracking ROIs differ from those in the reference mask. As shown in step S36, as active material degradation evaluation 2, the vanishing area calculation unit 78 calculates the vanishing of the tracking ROIs to evaluate, from the parameter χ, the extent to which the experiment includes a state in which only a contrast change that cannot be captured by tracking occurs. In other words, this parameter can be used as an index for evaluating the overall quality of color analysis.

[0124] [Correction by linear expansion function] Next, correction using a linear expansion function will be described. First, as shown in step S37, a line image is generated using the same method as in step S33. Next, as shown in step S38, expansion function correction is performed on the analysis ROI coordinates. The following description will be given with reference to the drawings.

[0125] FIG. 19 is a graph illustrating an expansion function and a contraction function in the electrochemical reaction visualization device 100 according to the second embodiment, where the horizontal axis represents time, the left vertical axis represents the expansion rate, and the right vertical axis represents voltage. FIG. 19 shows, for example, the results of analyzing the expansion rate in the Y-axis direction from a line image on a line along the Y direction of color image data. As shown in FIG. 19, the expansion rate of the secondary battery 1 in the Y-axis direction increases from 0 hours to 12 hours. This corresponds to an increase in voltage, which indicates that the secondary battery is being charged. On the other hand, the expansion rate of the secondary battery 1 in the Y-axis direction decreases from 12 hours to 20 hours. This corresponds to a decrease in voltage, which indicates that the secondary battery is being discharged.

[0126] The linear expansion coefficient calculation unit 79 calculates the linear expansion coefficient in the Y direction (e.g., the second direction) of the tracking ROI in each state of charge. Then, the linear expansion coefficient calculation unit 79 approximates the time change in the linear expansion coefficient in the Y-axis direction from 0 to 12 hours and the time change in the linear expansion coefficient in the Y-axis direction from 12 to 20 hours using a polynomial or the like (or creates a lookup table). For example, the linear expansion coefficient calculation unit 79 calculates an expansion function that approximates the increase in the linear expansion coefficient over time from 0 to 12 hours. Furthermore, the linear expansion coefficient calculation unit 79 calculates a contraction function that approximates the decrease in the linear expansion coefficient over time from 12 to 20 hours.

[0127] 20A and 20B are diagrams illustrating correction of analytical ROI coordinates using an expansion function in the electrochemical reaction visualization device according to embodiment 2. As shown in FIG. 20A, the initial Y coordinates of analytical ROI-A and analytical ROI-B are given by Ya and Yb. As shown in FIG. 20B, the corrected Y coordinates of analytical ROI-A and analytical ROI-B during charging can be calculated using the expansion function Ey(t) according to the following equations (7) and (8). Note that the origin of the Y coordinates is preferably set to the "fixed point" of drift correction.

[0128]

number

number

[0129] This type of correction can prevent the position of the analysis ROI from shifting from its relative position within the electrode due to expansion / contraction. This method makes it possible to limit the analysis region, such as color analysis, to the minimum necessary size. Limiting the analysis region as much as possible improves spatial resolution and reduces the calculation load of the analysis, which is necessary for reducing analysis costs.

[0130] Although the linear expansion coefficient calculation unit 79 calculates the linear expansion coefficient in the Y direction (e.g., the second direction), the invention is not limited to this and may calculate the linear expansion coefficient in at least one of the X direction (e.g., the first direction) and the Y direction (e.g., the second direction). Also, although the above explanation has been given on the expansion correction of the analysis ROI (analysis region), exactly the same correction can be applied to the expansion / contraction correction of the master ROI coordinates.

[0131] [Separation of active material and solid electrolyte] It is extremely difficult to separate the active material and solid electrolyte before charging (discharged state) by binarization processing using the same criteria for the entire color image data. However, if we focus only on the vicinity of the active material at a certain location, it is possible to separate them by binarization processing using hue or brightness. Therefore, within the tracking ROI in which the active material is tracked, binarization processing conditions for the active material and solid electrolyte are set for each tracking ROI. This makes it possible to accurately separate the active material and solid electrolyte. For example, the master extraction unit 73 and the slave extraction unit 74 may separate the active material portion from the portion other than the active material portion within each tracking ROI.

[0132] [Re-tracking] If the active material cannot be captured during tracking, a new master ROI is created during the analysis. This is assumed to be a quasi-master ROI. If tracking capture cannot be performed consistently throughout the charge / discharge process, tracking can be continued by referencing the quasi-master ROI created at several times.

[0133] In this way, as shown in step S34, a quasi-master mask may be created by re-tracking. Specifically, if the slave extraction unit 74 cannot track the position of the active material portion extracted by the master extraction unit 73, the master extraction unit 73 may select color image data of a charge state other than the fully charged state. The master extraction unit 73 may then extract a portion of the selected color image data whose brightness is equal to or greater than a predetermined threshold as the active material portion and extract a range surrounding the active material portion as a tracking ROI. Furthermore, the master extraction unit 73 may generate a quasi-master ROI including multiple tracking ROIs, and generate a quasi-master mask from the generated quasi-master ROI, in which the tracking ROI portion is a valid region and the region other than the tracking ROI is an invalid region. Note that the quasi-master mask may be used as the reference mask in the above-mentioned [Active Material Deterioration Evaluation 1] and [Active Material Deterioration Evaluation 2].

[0134] Although the embodiments of the present invention have been described above, the present invention includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-described embodiments. Furthermore, the configurations in the first and second embodiments may be combined as appropriate.

[0135] The technical idea of ​​the embodiment also includes the following electrochemical reaction visualization program that causes a computer to execute the electrochemical reaction visualization method of the embodiment.

[0136] An electrochemical reaction visualization program for visualizing state changes during charging and discharging of a secondary battery, an observation cell having a transparent window and housing the secondary battery containing an active material whose luminance increases when fully charged; a charge / discharge controller that controls the charging / discharging so that the battery passes through a plurality of charge states with different charge amounts during the charging / discharging; a color confocal imaging unit that illuminates the secondary battery with illumination light through the transparent window and has an objective lens that transmits light reflected from the secondary battery from the illumination light, and acquires color image data of the secondary battery while changing the relative distance between the objective lens and the secondary battery; a data acquisition step of acquiring the color image data of each charge state of the secondary battery and charge / discharge data of each charge state from an electrochemical reaction visualization device comprising: a linking step of associating the color image data with the charge / discharge data in time series; a master extraction step of selecting the color image data of the fully charged state, extracting a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as the active material portion, and extracting a range surrounding the active material portion as a tracking ROI; a slave extraction step of tracking the position of the extracted active material portion in the color image data corresponding to each state of charge and extracting a range surrounding the tracked active material portion as the tracking ROI; An electrochemical reaction visualization program that runs on a computer.

[0137] Furthermore, the electrochemical reaction visualization program described above includes a set of instructions (or software code) that, when loaded into a computer, causes the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals. [Explanation of symbols]

[0138] 1 Secondary battery 2 Positive current collector plate 3 Cathode active material layer 4 Separator 5 Negative electrode active material layer 6 Negative current collector plate 10 Windowed Cell 10a, 10b connection terminals 19 Transparent Window 20 Charge / Discharge Controller 30 Color confocal imaging unit 31 Lighting source 32 Beam Splitter 33 2D scanner 34 Objective Lens 35 motor 36 Distance Sensor 37 Image acquisition unit 50 Signal processing section 51 Input Device 52 monitors 53 Clock Device 54 Omnifocal image forming means 55 First Memory 56 Three-dimensional image forming means 57 Second Memory 58 The Third Memory 59 SOC calculation means 60 The Fourth Memory 61 Output Method 70 Image processing section 71 Acquisition Department 72 Link section 73 Master Extraction 74 Slave Extractor 75 Color analysis section 76 Drift correction section 77 Overlap calculation section 78 Vanishing area calculation part 79 Linear expansion coefficient calculation section 100 Electrochemical reaction visualization device

Claims

1. An electrochemical reaction visualization device that visualizes state changes during charging and discharging of a secondary battery, a windowed cell having a transparent window and housing the secondary battery containing an active material that exhibits high luminance in a fully charged state; a charge / discharge controller that controls the charging / discharging so that the battery passes through a plurality of charge states with different charge amounts during the charging / discharging; a color confocal imaging unit that illuminates the secondary battery with illumination light through the transparent window and has an objective lens that transmits light reflected from the secondary battery from the illumination light, and acquires color image data of the secondary battery while changing the relative distance between the objective lens and the secondary battery; an image processing unit that acquires the color image data of each charge state of the secondary battery and charge / discharge data of each charge state; Equipped with The image processing unit a linking unit that associates the color image data with the charge / discharge data in chronological order; a master extraction unit that selects the color image data of the fully charged state, extracts a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as an active material portion, and extracts a range surrounding the active material portion as a tracking ROI; a slave extraction unit that tracks the position of the extracted active material portion in the color image data corresponding to each state of charge and extracts a range surrounding the tracked active material portion as the tracking ROI; having Electrochemical reaction visualization device.

2. the image processing unit further includes a color analysis unit that converts the RGB luminance of the active material portion into a hue to analyze each state of charge; The electrochemical reaction visualization device according to claim 1 .

3. The master extraction unit generating a master ROI that includes a plurality of said tracking ROIs; generating a master mask from the generated master ROI, the master mask having the tracking ROI as a valid region and the region other than the tracking ROI as an invalid region; The slave extraction unit generating a slave ROI including a plurality of said tracking ROIs; generating a slave mask from the generated slave ROI, the slave mask having the tracking ROI portion as a valid region and the portion other than the tracking ROI as an invalid region; The electrochemical reaction visualization device according to claim 1 or 2.

4. the image processing unit further includes an overlap calculation unit that calculates an overlap of the tracking ROI from a difference between a sum of areas of the tracking ROIs included in the master mask or the slave mask that is a reference mask and a sum of areas of the tracking ROIs included in the master mask or the slave mask that is different from the reference mask; The electrochemical reaction visualization device according to claim 3 .

5. The image processing unit further includes an overlap calculation unit that calculates an overlap of at least one of the lengths in the first direction and the second direction of the tracking ROIs from a difference between at least one of a sum of lengths in a first direction and a sum of lengths in a second direction orthogonal to the first direction of each tracking ROI included in the master mask or the slave mask that is a reference mask, and at least one of a sum of lengths in the first direction and a sum of lengths in the second direction of each tracking ROI included in the master mask or the slave mask that is different from the reference mask. The electrochemical reaction visualization device according to claim 3 or 4.

6. the image processing unit further includes a disappearance area calculation unit that calculates an area of ​​the tracking ROI of the master mask or the slave mask that is used as a reference mask, the disappearance area being calculated when the corresponding tracking ROI is different from the reference mask in the master mask or the slave mask. The electrochemical reaction visualization device according to claim 3 .

7. a linear expansion coefficient calculation unit that calculates a linear expansion coefficient of at least one of a first direction of the tracking ROI and a second direction orthogonal to the first direction in each charging state; the linear expansion coefficient calculation unit calculates at least one of an expansion function that approximates an increase in the linear expansion coefficient with respect to time and a contraction function that approximates a decrease in the linear expansion coefficient with respect to time. The electrochemical reaction visualization device according to claim 3 .

8. the windowed cell includes a fixed point; the color image data is captured so as to include the fixed point; the image processing unit further includes a drift correction unit that tracks the fixed points in the plurality of pieces of color image data and corrects positional deviations of the color image data so that the fixed points are at the same position. The electrochemical reaction visualization device according to any one of claims 1 to 7.

9. the master extractor and the slave extractor separate the active material portion within each tracking ROI from a portion other than the active material portion; The electrochemical reaction visualization device according to any one of claims 1 to 8.

10. When the slave extraction unit cannot track the position of the active material portion extracted by the master extraction unit, The master extraction unit Select the color image data of the charging state other than the fully charged state, extracting a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as the active material portion; extracting a region surrounding the active material portion as a tracking ROI; generating a quasi-master ROI including a plurality of said tracking ROIs; generating a quasi-master mask from the generated quasi-master ROI, in which the tracking ROI portion is a valid region and the portion other than the tracking ROI is a invalid region; The electrochemical reaction visualization device according to any one of claims 1 to 9.

11. An electrochemical reaction visualization method for visualizing a state change during charging and discharging of a secondary battery, comprising: a windowed cell having a transparent window and housing the secondary battery containing an active material that exhibits high luminance in a fully charged state; a charge / discharge controller that controls the charging / discharging so that the battery passes through a plurality of charge states with different charge amounts during the charging / discharging; a color confocal imaging unit that illuminates the secondary battery with illumination light through the transparent window and has an objective lens that transmits light reflected from the secondary battery from the illumination light, and acquires color image data of the secondary battery while changing the relative distance between the objective lens and the secondary battery; a data acquisition step of acquiring the color image data of each charge state of the secondary battery and charge / discharge data of each charge state from an electrochemical reaction visualization device comprising: a linking step of associating the color image data with the charge / discharge data in time series; a master extraction step of selecting the color image data in the fully charged state, extracting a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as an active material portion, and extracting a range surrounding the active material portion as a tracking ROI; a slave extraction step of tracking the position of the extracted active material portion in the color image data corresponding to each state of charge and extracting a range surrounding the tracked active material portion as the tracking ROI; An electrochemical reaction visualization method comprising:

12. The method further includes a color analysis step of converting the RGB luminance of the active material portion into a hue to analyze each state of charge. The electrochemical reaction visualization method according to claim 11.

13. The master extraction step comprises: generating a master ROI that includes a plurality of said tracking ROIs; generating a master mask from the generated master ROI, the master mask having the tracking ROI as a valid region and the region other than the tracking ROI as an invalid region; The slave extraction step includes: generating a slave ROI including a plurality of said tracking ROIs; generating a slave mask from the generated slave ROI, the slave mask having the tracking ROI portion as a valid region and the portion other than the tracking ROI as an invalid region; The electrochemical reaction visualization method according to claim 11 or 12.

14. further comprising an overlap calculation step of calculating an overlap of the tracking ROI from a difference between a sum of areas of the tracking ROIs included in the master mask or the slave mask that is a reference mask and a sum of areas of the tracking ROIs included in the master mask or the slave mask that is different from the reference mask; The electrochemical reaction visualization method according to claim 13.

15. an overlap calculation step of calculating an overlap of at least one of the lengths in the first direction and the second direction of the tracking ROI from a difference between at least one of the sum of the lengths in a first direction and the sum of the lengths in a second direction orthogonal to the first direction of the tracking ROI included in the master mask or the slave mask that is a reference mask, and at least one of the sum of the lengths in the first direction and the sum of the lengths in the second direction of the tracking ROI included in the master mask or the slave mask that is different from the reference mask, The electrochemical reaction visualization method according to claim 13 or 14.

16. The method further includes a disappearance area calculation step of calculating an area of ​​the tracking ROI of the master mask or the slave mask that is used as a reference mask, the area of ​​which has disappeared in the master mask or the slave mask where the corresponding tracking ROI is different from the reference mask. The electrochemical reaction visualization method according to claim 13.

17. The method further includes a linear expansion coefficient calculation step of calculating a linear expansion coefficient of at least one of a first direction of the tracking ROI and a second direction orthogonal to the first direction in each charging state, the linear expansion coefficient calculation step calculates at least one of an expansion function that approximates an increase in the linear expansion coefficient with respect to time and a contraction function that approximates a decrease in the linear expansion coefficient with respect to time. The electrochemical reaction visualization method according to claim 13.

18. the windowed cell includes a fixed point; the color image data is captured so as to include the fixed point; a drift correction step of tracking the fixed point in the plurality of pieces of color image data and correcting positional deviation of each piece of color image data so that the fixed point is at the same position; The electrochemical reaction visualization method according to any one of claims 11 to 17.

19. the master extraction step and the slave extraction step separate the active material portion within each tracking ROI from a portion other than the active material portion; An electrochemical reaction visualization method according to any one of claims 11 to 18.

20. When the position of the active material portion extracted in the master extraction step cannot be tracked in the slave extraction step, selecting the color image data of the charge state other than the fully charged state, extracting a portion of the selected color image data where the brightness is equal to or greater than a predetermined threshold as the active material portion, and extracting a range surrounding the active material portion as a tracking ROI; generating a quasi-master ROI including a plurality of said tracking ROIs; The method further comprises a quasi-master extraction step of generating a quasi-master mask from the generated quasi-master ROI, in which the tracking ROI portion is defined as a valid region and a region other than the tracking ROI is defined as an invalid region. An electrochemical reaction visualization method according to any one of claims 11 to 19.

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