JP7778010B2 - Electrochemical reaction visualization device and electrochemical reaction visualization method - Google Patents

Description

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 an uncharged state in which the active material and electrolyte cannot be distinguished by color or brightness.

In order to evaluate the impact on secondary battery performance, such as the uniformity of electrochemical reactions inside the secondary battery, local overcharging, and physical changes such as temperature and expansion, it is necessary to dynamically visualize the distribution of the state of charge.

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

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

Patent No. 5388078 JP 2013-239263 A Japanese Patent Application Laid-Open No. 2017-212163 JP 2014-089969 A Japanese Patent Application Laid-Open No. 2021-021579

In secondary batteries that use a transparent electrolyte, such as conventional lithium-ion batteries, the electrolyte and active material can be easily distinguished when observing the charge/discharge state in situ using a color confocal microscope. This is because the light reflected from the interface between the electrolyte and the observation window is removed by the confocal optical system, allowing only the interfacial reflection between the electrolyte and active material to be observed. Because the space outside the active material particles in the electrode is porous, it is filled with electrolyte, and there is almost no light reflected from pores where there is no active material. In this case, it is relatively easy to distinguish between the active material and other areas based on brightness and hue.

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 be of similar brightness. In particular, the brightness and hue of the uncharged active material are very similar to those of 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. There is a demand for an apparatus and method for easily distinguishing between active material and (solid) electrolyte.

The object of the present invention is to solve these problems by providing an electrochemical reaction visualization device and electrochemical reaction visualization method that can easily distinguish between active materials and electrolytes.

The electrochemical reaction visualization device according to the present disclosure is an electrochemical reaction visualization device that visualizes state changes during charging and discharging of a secondary battery, and includes: a windowed 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 charging and discharging so that the secondary battery passes through multiple charge states with different charge amounts during charging and 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 by the illumination light from 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; and a color image sensor that captures 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 and charge/discharge data for each charge state. The image processing unit has a linking unit that chronologically associates the color image data and the charge/discharge data, a master extraction unit that selects the color image data for the fully charged state, extracts portions of the selected color image data where the brightness is equal to or greater than a predetermined threshold as active material portions, and extracts a range surrounding the active material portions as a tracking ROI, and a slave extraction unit that tracks the position of the extracted active material portions in the color image data corresponding to each charge state, and extracts a range surrounding the tracked active material portions as the tracking ROI.

In the above-mentioned electrochemical reaction visualization device, the image processing unit may further include a color analysis unit that analyzes each charging state by converting the RGB brightness of the active material portion into hue.

In the electrochemical reaction visualization device, the master extraction unit may generate a master ROI including multiple tracking ROIs and generate a master mask from the generated master ROI in which the tracking ROIs are defined as valid regions and the rest of the area is defined as invalid regions; and the slave extraction unit may generate a slave ROI including multiple tracking ROIs and generate a slave mask from the generated slave ROI in which the tracking ROIs are defined as valid regions and the rest of the area is defined as invalid regions.

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 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 slave mask that is different from the reference mask.

In the electrochemical reaction visualization device, the image processing unit may further include an overlap calculation unit that calculates the overlap of at least one of the lengths of the tracking ROIs in the first direction and the second direction from the difference between 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 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.

In the electrochemical reaction visualization device, the image processing unit may further include a disappearance 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, when the corresponding tracking ROI in the master mask or the slave mask differs from the reference mask.

The electrochemical reaction visualization device may further include a linear expansion coefficient calculation unit that calculates the linear expansion coefficient of at least one of a first direction of the tracking ROI and a second direction perpendicular to the first direction in each charging state, 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.

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

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

In the electrochemical reaction visualization device, if 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 for 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 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 portion other than the tracking ROI is a invalid region.

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, and includes: an electrochemical reaction visualization device including a windowed cell that houses a secondary battery having a transparent window and containing an active material whose luminance increases when fully charged; a charge/discharge controller that controls charging and discharging so that the secondary battery passes through multiple charge states with different charge amounts during 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 illumination light from 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 portions of the selected color image data where the brightness is equal to or greater than a predetermined threshold as active material portions, and extracting a range surrounding the active material portions as a tracking ROI; and a slave extraction step of tracking the position of the extracted active material portions in the color image data corresponding to each charge state, and extracting a range surrounding the tracked active material portions as the tracking ROI.

The electrochemical reaction visualization method may further include a color analysis step of converting the RGB brightness of the active material portion into hue to analyze each charging state.

In the electrochemical reaction visualization method, the master extraction step may generate a master ROI including multiple tracking ROIs, and generate a master mask from the generated master ROI in which the tracking ROIs are defined as valid regions and the rest of the region is defined as invalid regions; and the slave extraction step may generate a slave ROI including multiple tracking ROIs, and generate a slave mask from the generated slave ROI in which the tracking ROIs are defined as valid regions and the rest of the region is defined as invalid regions.

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 slave mask used as a 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.

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

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 are used as a reference mask, where the corresponding tracking ROIs in the master mask or the slave mask differ from those in the reference mask.

The electrochemical reaction visualization method may further include a linear expansion coefficient calculation step for calculating the linear expansion coefficient of at least one of a first direction of the tracking ROI and a second direction perpendicular to the first direction in each charging state, 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 as it increases over time and a contraction function that approximates the change in the linear expansion coefficient as it decreases over time.

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 multiple pieces of color image data and correcting positional deviations in each piece of color image data so that the fixed point is in the same position.

In the above-described electrochemical reaction visualization method, the master extraction step and the slave extraction step may separate the active material portion within each tracking ROI from the portion other than the active material portion.

The electrochemical reaction visualization method may further include a quasi-master extraction step of, if 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 for 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 multiple tracking ROIs, and generating a quasi-master mask from the generated quasi-master ROI in which the tracking ROI portion is an effective region and the portion other than the tracking ROI is an ineffective region.

The present invention provides an electrochemical reaction visualization device and electrochemical reaction visualization method that can easily distinguish between active materials and electrolytes and analyze changes in the state of secondary batteries during charging and discharging.

1 is a configuration diagram illustrating an electrochemical reaction visualization device according to a first embodiment. FIG. 2 is a diagram illustrating a windowed cell in the electrochemical reaction visualization device according to the first embodiment. FIG. 2 is a block diagram illustrating a signal processing unit in the electrochemical reaction visualization device according to the first embodiment. FIG. 2 is a block diagram illustrating an image processing unit in the electrochemical reaction visualization device according to the first embodiment. 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. 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. 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. FIG. 2 is a conceptual diagram illustrating tracking of an active material in the electrochemical reaction visualization method according to the first embodiment. FIG. 10 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. FIG. 10 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. 1A and 1B are diagrams 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. FIG. 3 is a diagram illustrating a tracking ROI in the electrochemical reaction visualization method according to the first embodiment. FIG. 3 is a diagram illustrating a master mask in the electrochemical reaction visualization method according to the first embodiment. 5A to 5C 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. FIG. 1 is a flowchart illustrating an electrochemical reaction visualization method according to a first embodiment. 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. 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. 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. FIG. 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. 1 is a graph illustrating an example of an analysis result of an average score in the electrochemical reaction visualization method according to the first embodiment, in which the horizontal axis represents time and the vertical axis represents the average score. 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. FIG. 10 is a block diagram illustrating an image processing unit in the electrochemical reaction visualization device according to the second embodiment. FIG. 10 is a flowchart illustrating an electrochemical reaction visualization method according to a second embodiment. 10A and 10B are diagrams illustrating line images in the electrochemical reaction visualization device according to the second embodiment. 10A and 10B are diagrams illustrating line images in the electrochemical reaction visualization device according to the second embodiment. 10A and 10B are diagrams illustrating line images in the electrochemical reaction visualization device according to the second embodiment. 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. 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. FIG. 10 is a diagram illustrating an example of overlapping of tracking ROIs in the electrochemical reaction visualization device according to the second embodiment. 10 is a graph illustrating an expansion function and a contraction function in an electrochemical reaction visualization device according to embodiment 2, where the horizontal axis represents time, the left vertical axis represents the expansion rate, and the right vertical axis represents voltage. FIG. 10 is a diagram illustrating correction of analysis ROI coordinates using an expansion function in the electrochemical reaction visualization device according to the second embodiment. FIG. 10 is a diagram illustrating correction of analysis ROI coordinates using an expansion function in the electrochemical reaction visualization device according to the second embodiment.

The specific configuration of this embodiment will be described below with reference to the drawings. The following description illustrates 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 similar content.

(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.

[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. In addition to the above, the electrochemical reaction visualization device 100 may also include an image data storage, a general-purpose information processing device, and the like. 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.

<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.

Figure 2 is a diagram illustrating a windowed cell 10 in the electrochemical reaction visualization device 100 according to embodiment 1. As shown in Figures 1 and 2, the windowed cell 10 is designed to allow observation of a cross section of the secondary battery 1. The windowed cell 10 has a windowed lid and a cell body.

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 referred to as the positive electrode, and the negative electrode active material layer 5 and the negative electrode current collector 6 are referred to as the negative electrode. For example, rolled aluminum foil is used as the positive electrode current collector 2, and a lithium cobalt oxide (LiCoO ₂ ) 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 the positive electrode and the negative electrode. The positive electrode and the negative electrode are filled with an electrolyte, which is an organic electrolyte obtained by dissolving a lithium salt such as LiPF ₆ in an organic solvent such as ethylene carbonate (EC).

The secondary battery 1 is formed 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 the dedicated jig's blade. The electrode holder is then sealed in the cell body along with the electrolyte, and the electrode cross section is pressed against the transparent window 19 attached to the lid. In this way, the secondary battery 1 is observed. The work up to closing the lid is performed in a glove box or dry room, but after the lid is sealed, observations are made in the atmosphere. Gas may be generated during charge/discharge experiments. This not only interferes with observation, but also creates a dry, partially electrolyte-free state, which is a major obstacle. To avoid these obstacles, the dedicated windowed cell 10 has the function of excluding generated gas from the observation area.

When an all-solid-state battery is used as the secondary battery 1, impregnation with an electrolyte is not necessary. Furthermore, no separator is used. The secondary battery 1 is made 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 one that produces a difference in brightness between a fully charged state and a non-fully charged state. For example, the secondary battery 1 may be one that uses an electrolyte containing an active material whose brightness increases in a fully charged state, or it may be an all-solid-state battery.

<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 multiple 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 I0 ₊ terminal of the charge/discharge controller 20, which controls the charging and discharging of the secondary battery 1. The second connection terminal 10b is connected to the _I0- terminal of the charge/discharge controller 20.

As a charge/discharge control method, for example, charging can be performed using a constant current/constant voltage (CVCC) method. That is, charging is performed by supplying a constant current to the secondary battery 1 at the start of charging, and after full charge is achieved, charging is performed at a constant voltage. Discharge control can also be performed using constant current control. The first and second connection terminals 10a and 10b are connected to the V ₊ and _V- terminals of the charge/discharge controller 20, and a voltage detection means provided in the charge/discharge controller 20 detects the charge/discharge voltage (battery voltage) as time-series data. Furthermore, the charge/discharge controller 20 has a current detection means for detecting the current flowing through the secondary battery 1 and outputs the current value 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.

<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.

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.

The illumination beam that passes 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.

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 this is supplied to the 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 that has been corrected for plate thickness.

The illumination beam passes through the 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 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 across 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 (focused) of all uneven surfaces is captured.

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.

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

In this way, the color confocal imaging unit 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 unit 30 then 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 unit 30 constitutes a color confocal optical system, and high-resolution color confocal images are captured.

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 features of the color confocal imaging unit 30 are as follows:

[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. As a result, unlike a typical optical microscope, even if a transparent window 19 is present in front of the observation surface, it is possible to eliminate unnecessary scattered light from the transparent window 19. Furthermore, even when the observation surface is submerged in liquid, it is possible to eliminate unnecessary scattered light from the liquid, allowing the observation surface to be observed clearly.

[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.

When performing operando observation, data is acquired using the color confocal imaging unit 30 while charging and discharging using a charge/discharge program. This allows images to be captured, for example, every minute and the color observation images to be saved.

<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 analysis data to be output via the input device 51. The designated analysis data is displayed on the monitor 52.

Figure 3 is a block diagram illustrating the signal processing unit 50 in the electrochemical reaction visualization device 100 according to embodiment 1. As shown in Figure 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 the clock signal output from the clock device 53 as a common clock signal to link the color image data and 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 in pairs with the clock signal output from the clock device 53. Therefore, the clock device 53 and the memory function as linking means for linking the image data and charge/discharge data.

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 an 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 for the entire imaging area can be formed. Therefore, if there are irregularities in the cross section of the active material layer of the secondary battery 1, the omnifocal image forming means 54 forms a color image in focus on the irregular surface. The omnifocal image is formed at time intervals of, for example, one minute.

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

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. In other words, 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.

The formed 3D image signals are sequentially supplied to the second memory 57. The second memory 57 also receives clock information supplied from the clock device 53. The second memory 57 stores the input 3D image signals and clock signals as pairs.

The time-series charge/discharge data output from the charge/discharge controller 20 is supplied to the third memory 58. The clock signal output from the clock device 53 is also supplied to the third memory 58. The input charge/discharge data, i.e., charge/discharge voltage and charge/discharge current, are each stored as a pair with clock information. The charge/discharge data is supplied to the SOC calculation means 59, which determines the state of charge (SOC) after charging begins 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 a fully charged state being 100%. The calculated state of charge is stored in the fourth memory 60 along with the clock information. As a result, the state of charge linked to the image data is stored in the fourth memory 60.

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 along with the charge state. The charge/discharge data and 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.

<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.

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.

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, communication unit, memory unit, and interface unit (not shown). The control unit, communication unit, memory unit, and interface unit function as control means, communication means, memory means, and interface means, respectively.

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 and arithmetic processing. The control unit also controls the operation of the communication unit, memory unit, interface unit, and each component that executes the functions of each device.

Each component of each device can be realized, for example, by executing a program under the control of the 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 the storage unit. Alternatively, each component can be realized by recording the necessary programs on any non-volatile recording medium and installing them as needed. Furthermore, each component is not limited to being realized by software programs, but may also be realized by any combination of hardware, firmware, and software.

The communication unit performs the communications required for each device to process information. The storage unit is, for example, ROM (Read Only Memory) or RAM (Random Access Memory). The storage unit has the function of storing control programs and calculation programs executed by the control unit. The storage unit also has the function of temporarily storing processing data, etc.

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 (operator, etc.) and outputs information to the user. The functions of the image processing unit 70 are described below in the electrochemical reaction visualization method.

[Electrochemical reaction visualization method]
Next, the electrochemical reaction visualization method will be explained 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>.

<Overview>
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.

As shown in Figure 5A, the electrochemical reaction visualization method of this embodiment is based on the premise of distinguishing between active material A, which changes color depending on the charging state, and material B, which does not. For example, the observed color of graphite, a typical active material in all-solid-state batteries, changes stepwise (gray → blue → red → gold) depending on the charging state. 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, solid electrolytes (referred to as SEs) do not change color with charging and discharging like graphite. Therefore, in the uncharged state, the brightness and color of the active material are similar to the color of the SEs, making them difficult to distinguish from the image.

As shown in Figure 5B, in the uncharged state before charging, active material A, which changes color, and material B, which does not change color, are difficult to distinguish between because their colors are similar. On the other hand, as shown in Figure 5C, in the fully charged state, active material A changes color to gold. This makes it possible to distinguish active material A from material B. Therefore, in this embodiment, we extract only active material A, which changes color depending on the charging state, and quantify the color change to observe the relationship between the charging/discharging state (charging/discharging voltage) corresponding to the charging/discharging time and the color change.

Figure 6 is a conceptual diagram illustrating the tracking of active materials in the electrochemical reaction visualization method according to embodiment 1. As shown in Figure 6, in the initial state (a), which is an uncharged state, it is difficult to distinguish between active material A (e.g., graphite), which changes color when charged, and material B, which does not change color. As time passes during charging (b), the color of active material A, which changes color when charged, changes. Finally, in the fully charged state (c), active material A turns gold. Therefore, it is possible to distinguish between active material A and material B, which does not change color.

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%. The area surrounding the extracted active material A is then set as the tracking ROI.

Specifically, the master extraction unit 73 selects color image data for a fully charged state. The master extraction unit 73 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 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.

Next, for the tracking ROI, which is the range used to extract active material A, active material A is continued to be tracked 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).

Specifically, the slave extraction unit 74 tracks the position of the extracted active material portion in the color image data corresponding to each charge state. The slave extraction unit 74 extracts the 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.

<Generation of Tracking ROI>
Next, the generation of the tracking ROI will be described in detail. Figures 7A to 7C are diagrams illustrating a method for generating a tracking ROI 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 the tracking ROI.

As shown in Figure 7A, when extracting a tracking ROI, first select color image data for a fully charged state (SOC 100%) where the charge state is 100%. Next, as shown in Figure 7B, the color-changed active material portion AP is colored. Coloring is explained in the Color Analysis section. Then, as shown in Figure 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 frame is called the tracking ROI (also called 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 extracted tracking ROIs are extracted from the color image data, each tracking ROI is set to encompass the maximum length and width (XY) of the extracted active material portion.

Figure 8 is a diagram illustrating a tracking ROI in the electrochemical reaction visualization method according to embodiment 1. As shown in Figure 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. The size and shape of each tracking ROI set here are basically unchanged. However, the tracking ROI size may be changed when applying the tracking ROI to an image other than 100% SOC or when recreating it midway.

<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 includes 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."

Figure 9 is a diagram illustrating a master mask in the electrochemical reaction visualization method according to embodiment 1. As shown in Figure 9, the master extraction unit 73 generates a master mask from the generated master ROI, with the tracking ROI portion designated as the valid region and the region outside the tracking ROI designated as the invalid region. The master mask is also called an M-Mask. A master mask refers to a binary mask. By taking the logical product of the image to be analyzed and the master mask, it is possible to narrow down the analysis target to only the "valid region."

<Creating 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 of 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.

A mask generated from color image data other than the fully charged state is called a slave mask (S-Mask). A slave mask is generated as follows: The slave extraction unit 74 sets the tracking ROI in the master mask as the initial condition. The slave extraction unit 74 then tracks each tracking ROI in response to changes in the charging state, thereby generating multiple slave ROIs (S-ROIs). Each slave ROI includes multiple tracking ROIs.

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

<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 a memory in chronological order.

<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, for example, in the first memory 55. The acquisition unit 71 reads the color image data from the first memory 55.

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 color image data of the secondary battery 1 is captured. The charge/discharge data is stored, for example, in 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; 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.

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

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. Color analysis, which will be described later, may also be performed.

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 an area surrounding the extracted active material portion as a tracking ROI. The master extraction unit 73 also generates a master ROI that includes multiple tracking ROIs, and generates a master mask from the generated master ROI in which the tracking ROI portions are valid regions and portions other than the tracking ROIs are invalid regions. In this way, the master extraction unit 73 generates a master ROI and a master mask.

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 charge state. The slave extraction unit 74 extracts the 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 an effective region and the portion outside the tracking ROI is an ineffective region. In the tracking analysis, color analysis may also be performed as shown in step S43. Color analysis is described below.

<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 (e.g., a graphite negative electrode in a composite electrode) during charge/discharge. For example, the amount of Li in graphite, an active material, correlates with color change (blue → red → gold). Therefore, the RGB brightness can be converted into hue (also referred to as H) using the following formula (1), and the color change can be quantified.

Therefore, color analysis is performed as shown in step S43 of Figure 11. Specifically, the 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.

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 average score below is calculated.

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

In this way, by calculating the average point, it is possible to obtain the change in spatial distribution over time. For example, the thickness direction is the direction in which the current collecting band, negative electrode (graphite), and SE are stacked in this order. By specifying two areas separated in the thickness direction and calculating the average point of each area, it is possible to quantify the reaction distribution in the thickness direction of the secondary battery 1.

Before describing this embodiment, a comparative example will be described. Figure 12A is a diagram illustrating a designated area in a secondary battery 1 in an electrochemical reaction visualization method according to a comparative example. Figure 12B is a graph illustrating the analysis results of the 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. Figure 12C is a diagram illustrating the coloring of an extracted active material portion in an electrochemical reaction visualization method according to a comparative example.

As shown in Figure 12A, 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 foil-side analysis area (Area 2). Each area is referred to as the "analysis ROI." The separator-side analysis area (Area 1) and the current collector foil-side analysis area (Area 2) are separated in the thickness direction. As shown in Figure 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 Figure 12C, the comparative electrochemical reaction visualization method cannot distinguish between active materials such as graphite and SE, so the active materials and SE are analyzed together. Therefore, the state of charge (SOC) is recognized as 30%.

Next, this embodiment will be described. Figure 13A is a diagram illustrating a designated area in a secondary battery 1 in the electrochemical reaction visualization method according to embodiment 1. Figure 13B is a graph illustrating the analysis results 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. Figure 13C is a diagram illustrating the coloring of an extracted active material portion in the electrochemical reaction visualization method according to embodiment 1.

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 foil-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 the graphite. Therefore, color analysis can be performed on the active material portion, and is not affected by SE. This makes it possible to analyze only the graphite in an all-solid-state battery and determine the expected score. The reaction time difference can also be quantified.

Next, the effects of this embodiment will be described. The electrochemical reaction visualization device 100 of this embodiment extracts active material after the secondary battery 1 is fully charged. This makes it possible to clearly separate active material from non-active material. 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 at each charge state, it is possible to distinguish the active material from the electrolyte. In this way, this embodiment makes it possible to easily distinguish between active material and electrolyte at each charge state, thereby analyzing the charge state of the secondary battery 1.

In conventional secondary batteries 1 that use a transparent electrolyte, 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 that use an electrolyte that is 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 as they are charged are identified. Then, by tracking them across each charge state, the charge state distribution of the all-solid-state battery can be visualized.

Furthermore, this embodiment allows for highly accurate detection of the reaction distribution and reaction time of active materials through color analysis, even in the case of all-solid-state batteries.

(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 vanishing 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 vanishing area calculation unit 78, and the linear expansion coefficient calculation unit 79.

Figure 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).

The following sections, "Drift Correction," "Line Image Creation," "Active Material Degradation Evaluation 1," "Active Material Degradation Evaluation 2," "Correction Using Linear Expansion Function," "Separation of Active Material and Solid Electrolyte," and "Re-Tracking," explain each of the above-mentioned configurations and steps.

[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 line images 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 a drift correction value (ΔX, ΔY) so 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 the line image, as described below. Then, as shown in step S33, drift correction is performed by applying these drift correction values to all frames.

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 multiple color image data and corrects the positional deviation of each color image data so that the fixed point is in the same position.

This correction can remove sudden blurring of color image data. When calculating coordinate correction values, it is important to perform subpixel processing using bicubic interpolation, etc., to eliminate jerky effects caused by pixel size quantization.

[Line image creation]
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 embodiment 2. The line image is an image in which color image data obtained in time series at a predetermined position (e.g., 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 represents the passage of time, and the vertical axis represents, 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 the linear expansion function and contraction function described below (e.g., FIG. 16C).

[Active material deterioration evaluation 1]
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.

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 prevented from being analyzed redundantly in 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).

In this way, when calculating the overlap, 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 below, 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 used as the reference mask and the sum of the areas of the tracking ROIs included in a 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).

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

18 is a diagram illustrating an example of overlap of tracking ROIs in the electrochemical reaction visualization device 100 according to embodiment 2. 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 (e.g., the first direction) and the sum of the overlap lengths Ly in the Y direction (e.g., the second direction), the directionality of deformation and movement of the active material in the secondary battery 1 can be evaluated. 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 as ΣL _RX and ΣL _RY , respectively.

Here, when calculating the overlap, the master mask or slave mask used to calculate ΣL _RX and ΣL _RY is used as the reference mask. The reference mask may be any master mask or slave mask as long as it can calculate ΣL _RX and ΣL _RY . 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 of at least one of the X- and Y-direction lengths of the tracking ROIs included in the master mask or slave mask used as the reference mask, based on the difference between 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 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 racking ROIs.

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

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 below, may also be used as the reference mask. The disappearance area calculation unit 78 calculates the area of the disappearance in the master mask or slave mask whose corresponding tracking ROI differs from the reference mask, among the tracking ROIs of the master mask or slave mask used as the reference mask. As shown in step S36, for active material degradation evaluation 2, the disappearance area calculation unit 78 calculates the disappearance of the tracking ROI, and uses the parameter χ to evaluate the extent to which the experiment includes states in which the contrast change is so small that it cannot be captured by tracking. In other words, this parameter can be used as an index for evaluating the overall success of the color analysis.

[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 made with reference to the drawings.

Figure 19 is a graph illustrating the expansion function and contraction function in the electrochemical reaction visualization device 100 according to embodiment 2. The horizontal axis represents time, the left vertical axis represents the expansion rate, and the right vertical axis represents voltage. Figure 19 shows, for example, the results of analyzing the expansion rate in the Y-axis direction from a line image along the Y direction of color image data. As shown in Figure 19, from 0 hours to 12 hours, the expansion rate of the secondary battery 1 in the Y-axis direction increases. This corresponds to an increase in voltage, which indicates that the battery is being charged. On the other hand, from 12 hours to 20 hours, the expansion rate of the secondary battery 1 in the Y-axis direction decreases. This corresponds to a decrease in voltage, which indicates that the battery is being discharged.

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 at each charging state. The linear expansion coefficient calculation unit 79 then approximates the time change in the linear expansion coefficient in the Y-axis direction from 0 hours to 12 hours and the time change in the linear expansion coefficient in the Y-axis direction from 12 hours 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 hours to 12 hours. The linear expansion coefficient calculation unit 79 also calculates a contraction function that approximates the decrease in the linear expansion coefficient over time from 12 hours to 20 hours.

Figures 20A and 20B are diagrams illustrating the correction of analytical ROI coordinates using an expansion function in the electrochemical reaction visualization device according to embodiment 2. As shown in Figure 20A, the initial Y coordinates of analytical ROI-A and analytical ROI-B are given by Ya and Yb. As shown in Figure 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 it is preferable to set the origin of the Y coordinate at the "fixed point" of drift correction.

This type of correction prevents the position of the analysis ROI from shifting from its relative position within the electrode due to expansion and contraction. This method makes it possible to limit the analysis area, such as color analysis, to the minimum necessary size. Limiting the analysis area as much as possible improves spatial resolution and reduces the calculation load of the analysis, making it a necessary process for reducing analysis costs.

Note that while the linear expansion coefficient calculation unit 79 calculated the linear expansion coefficient in the Y direction (e.g., the second direction), this is not limiting and the linear expansion coefficient may be calculated in at least one of the X direction (e.g., the first direction) and the Y direction (e.g., the second direction). Furthermore, while the above explanation describes expansion correction of the analysis ROI (analysis region), the same correction can also be applied to expansion/contraction correction of the master ROI coordinates.

[Separation of active material and solid electrolyte]
It is extremely difficult to separate the active material and solid electrolyte before charging (discharged state) using the same criteria for the entire color image data through binarization processing. However, if only the vicinity of the active material at a certain location is focused on, separation is possible through binarization processing, etc., 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.

[Re-tracking]
If the active material cannot be captured during tracking, a new master ROI is created during the analysis. This ROI 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.

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, as the active material portion, a portion of the selected color image data whose brightness is equal to or greater than a predetermined threshold, 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 from the generated quasi-master ROI, generate a quasi-master mask in which the tracking ROI portion is the valid region and the region outside the tracking ROI is the 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].

The above describes embodiments of the present invention, but the present invention includes appropriate modifications that do not impair its objects and advantages, and is not limited to the above embodiments. Furthermore, the configurations in embodiments 1 and 2 may be combined as appropriate.

The technical concept 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.

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 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 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.

The electrochemical reaction visualization program described above also includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored on 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 devices. The program may also be transmitted on a temporary computer-readable medium or communication medium. By way of example and not limitation, temporary computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

1 Secondary battery 2 Positive electrode current collector 3 Positive electrode active material layer 4 Separator 5 Negative electrode active material layer 6 Negative electrode current collector 10 Windowed cell 10a, 10b Connection terminal 19 Transparent window 20 Charge/discharge controller 30 Color confocal imaging unit 31 Illumination light source 32 Beam splitter 33 Two-dimensional scanner 34 Objective lens 35 Motor 36 Distance sensor 37 Image acquisition unit 50 Signal processing unit 51 Input device 52 Monitor 53 Clock device 54 All-focus image forming means 55 First memory 56 Three-dimensional image forming means 57 Second memory 58 Third memory 59 SOC calculation means 60 Fourth memory 61 Output means 70 Image processing unit 71 Acquisition unit 72 Link unit 73 Master extraction unit 74 Slave extraction unit 75 Color analysis unit 76 Drift correction unit 77 Overlap calculation unit 78 Vanishing area calculation unit 79 Linear expansion coefficient calculation unit 100 Electrochemical reaction visualization device

Claims (20)

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. 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 . 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. 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 . 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. 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 . 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 . 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. 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. 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. 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: 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. 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. 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. 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. 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. 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. 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. 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. 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.