Evaluation method for battery member

Abstract

The main purpose of the present disclosure is to provide a battery member evaluation method capable of quantitatively evaluating the positional relationship (distribution state) between a first element and a second element. In the present disclosure, the problem is solved by providing a method for evaluating a battery member containing a first element and a second element, the method comprising an image acquisition step, a binarization step, and a calculation step, the image acquisition step acquires a mapped image A of the first element and a mapped image B of the second element in a cross section of the battery member, and the binarization step binarizes each of the mapped image A and the mapped image B to create a binarized image a and a binarized image b. The calculation step calculates a correlation coefficient between the first element and the second element by superimposing the binarized image a and the binarized image b.

Description

Technical Field

[0001] This disclosure relates to evaluation methods for battery components. Background Technology

[0002] In recent years, battery development has been booming. For example, in the automotive industry, the development of batteries for use in battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), or hybrid electric vehicles (HEVs) is underway. Batteries typically have a positive electrode layer and a negative electrode layer as electrode layers, with an electrolyte layer between the positive and negative electrode layers. For example, Patent Document 1 discloses a negative electrode layer containing Si-based active materials.

[0003] Existing technical documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2023-044620 Summary of the Invention

[0005] As components constituting a battery (battery components), examples include the electrode layer and the electrolyte layer. In addition to the active material, the electrode layer sometimes contains a solid electrolyte, a binder, and a conductive material. Similarly, the electrolyte layer sometimes contains a solid electrolyte and a binder. When a battery component contains a first element (e.g., the active material) and a second element (e.g., the solid electrolyte or the binder), the positional relationship (distribution state) of the first and second elements has a significant impact on battery performance.

[0006] This disclosure was made in view of the above circumstances, and its main purpose is to provide an evaluation method for battery components that can quantitatively evaluate the positional relationship (distribution state) of the first and second elements.

[0007] [1] An evaluation method for battery components, which is an evaluation method for battery components containing a first element and a second element, comprising an image acquisition process, a binarization process, and a calculation process.

[0008] The above image acquisition process acquires a mapped image A of the first element and a mapped image B of the second element in the cross-section of the battery component.

[0009] The above binarization process binarizes the mapped image A and the mapped image B respectively, creating binarized image a and binarized image b.

[0010] The above calculation process overlaps the binarized image a and the binarized image b and calculates the correlation coefficient between the first element and the second element.

[0011] [2] According to the evaluation method of the battery component described in [1], the battery component is a positive electrode layer, a negative electrode layer or a solid electrolyte layer.

[0012] [3] According to the evaluation method of battery components described in [1] or [2],

[0013] The first element mentioned above is a constituent element of the active substance.

[0014] The second element mentioned above is either a constituent element of a solid electrolyte or a dyeing element used to color the adhesive.

[0015] [4] The evaluation method for battery components according to any one of [1] to [3],

[0016] The first element mentioned above is Si.

[0017] The second element mentioned above is an S element, an Os element, or a Ru element.

[0018] [5] The evaluation method for battery components according to any one of [1] to [4],

[0019] In the above image acquisition process, the mapped image C of the third element is obtained.

[0020] In the above binarization process, the mapped image C is binarized to create a binarized image c.

[0021] In the above calculation process, at least one of the following is performed: overlapping the binarized image a and the binarized image c and calculating the correlation coefficient of the first element and the third element, and overlapping the binarized image b and the binarized image c and calculating the correlation coefficient of the second element and the third element.

[0022] The evaluation method for battery components disclosed herein is effective in quantitatively evaluating the positional relationship (distribution state) between the first and second elements. Attached Figure Description

[0023] Figure 1 This is a schematic cross-sectional view of an example battery.

[0024] Figure 2 This is a flowchart illustrating the evaluation method for battery components in this disclosure.

[0025] Figure 3 This is a graph illustrating the correlation coefficient between Si and Os.

[0026] Figure 4 It is a mapped image of Si.

[0027] Figure 5 For the mapped and binarized images of Os.

[0028] Figure 6 It is an image that overlaps the binarized images of Si and Os.

[0029] Explanation of reference numerals in the attached figures

[0030] 1… Positive electrode layer

[0031] 2… Negative electrode layer

[0032] 3…Electrolyte layer

[0033] 4…Positive current collector

[0034] 5… Negative current collector

[0035] 10… batteries Detailed Implementation

[0036] The following provides a detailed description of the evaluation method for the battery components and the method for setting the manufacturing conditions for the battery components in this disclosure.

[0037] A. Evaluation methods for battery components

[0038] Figure 1 This is a schematic cross-sectional view of an example battery. Figure 1 The battery 10 shown has a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive current collector 4 for collecting current in the positive electrode layer 1, and a negative current collector 5 for collecting current in the negative electrode layer 2. In this disclosure, a battery component refers to a component constituting the battery 10. Furthermore, in this disclosure, the battery component being evaluated can be any one of the positive electrode layer 1, the negative electrode layer 2, the electrolyte layer 3, the positive current collector 4, and the negative current collector 5, wherein the positive electrode layer 1, the negative electrode layer 2, or the electrolyte layer 3 is preferred. The battery component contains a first element (e.g., an active material) and a second element (e.g., a solid electrolyte or a binder).

[0039] Figure 2 This is a flowchart illustrating the evaluation method for battery components in this disclosure. For example... Figure 2 As shown, in the battery component evaluation method disclosed herein, firstly, a mapped image A of the first element and a mapped image B of the second element are obtained from the cross-section of the battery component (image acquisition step). Next, mapped images A and B are binarized respectively to create binarized images a and b (binarization step). Then, binarized images a and b are overlapped, and the correlation coefficient between the first and second elements is calculated (calculation step).

[0040] According to this disclosure, the positional relationship (distribution state) of the first and second elements can be quantitatively evaluated by calculating the correlation coefficient between the first and second elements. As mentioned above, when a battery component contains a first element (e.g., an active material) and a second element (e.g., a solid electrolyte or binder), the positional relationship (distribution state) of the first and second elements has a significant impact on battery performance.

[0041] For example, in the case of active materials such as Si-based active materials, which exhibit large volume changes due to charging and discharging, it may be possible to suppress these volume changes by increasing the amount of binder disposed around the active material. Previously, there were no quantitative indicators to evaluate how the second element (binder) is distributed relative to the first element (active material). In contrast, in this disclosure, by calculating the correlation coefficient between the first element (active material) and the second element (binder), the positional relationship (distribution state) of the first element (active material) and the second element (binder) can be quantitatively evaluated.

[0042] Furthermore, to create a good ion conduction pathway, a solid electrolyte needs to be appropriately positioned around the active material. Previously, there were no quantitative indicators to evaluate how the second element (solid electrolyte) is distributed relative to the first element (active material). In contrast, in this disclosure, by calculating the correlation coefficient between the first element (active material) and the second element (solid electrolyte), the positional relationship (distribution state) of the first element (active material) and the second element (solid electrolyte) can be quantitatively evaluated.

[0043] 1. Battery components

[0044] The battery component in this disclosure is a component that constitutes a battery. The battery can be a liquid-system battery or a solid-state battery. The battery component being evaluated may, for example, be... Figure 1 The positive electrode layer 1, negative electrode layer 2, electrolyte layer 3, positive current collector 4, and negative current collector 5 are selected from the above, wherein the positive electrode layer 1, negative electrode layer 2, or electrolyte layer 3 are preferred.

[0045] The positive electrode layer contains at least a positive electrode active material, and may further contain at least one of a solid electrolyte, a binder, and a conductive material. Examples of positive electrode active materials include LiCoO2 and LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and other layered active substances in rock salt, LiMn2O4, Li(Ni) 0.5 Mn 1.5 Spinel-type active materials such as O4 and olivine-type active materials such as LiFePO4. Additionally, sulfur (S) can also be used as a positive electrode active material.

[0046] Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complex hydride solid electrolytes. Sulfide solid electrolytes preferably contain Li, Me (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. Additionally, sulfide solid electrolytes may also contain halogen elements such as F, Cl, Br, and I.

[0047] Examples of adhesives include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), styrene-butadiene-styrene block copolymer (SBS), and styrene-isoprene-styrene block copolymer (SIS). When the adhesive contains unsaturated bonds, these unsaturated bonds react with OsO4 (osmium oxide), thereby coloring the adhesive. RuO4 (ruthenium oxide) can also be used instead of OsO4. Additionally, examples of conductive materials include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0048] The negative electrode layer contains at least a negative electrode active material, and may further contain at least one of a solid electrolyte, a binder, and a conductive material. Examples of negative electrode active materials include Si-based active materials and lithium titanate. Examples of Si-based active materials include elemental Si, Si alloys, Si oxides, and Si carbides. Si-based active materials can be porous. Examples of lithium titanate include Li₄Ti₅O₂. 12 The solid electrolyte, binder, and conductive materials used in the negative electrode layer are the same as described above. Additionally, the electrolyte layer preferably contains a solid electrolyte and a binder. The solid electrolyte and binder used in the electrolyte layer are the same as described above.

[0049] The battery component contains a first element and a second element. The first element is preferably a constituent element of the active material, a constituent element of the solid electrolyte, or a dyeing element used to color the binder, with the former being the preferred constituent element of the active material. For example, if the active material is a Si-based active material, the first element is preferably Si, a constituent element of the Si-based active material. On the other hand, if the solid electrolyte is a sulfide solid electrolyte, the first element can be S, a constituent element of the sulfide solid electrolyte. Furthermore, if the binder has unsaturated bonds, the first element can also be a dyeing element used to color the binder (e.g., Os or Ru). The second element is a component different from the first element, preferably a constituent element of the active material, a constituent element of the solid electrolyte, or a dyeing element used to color the binder, with the latter being the preferred constituent element of the solid electrolyte or a dyeing element used to color the binder. The same applies to these elements as described above.

[0050] 2. Image acquisition process

[0051] The image acquisition process in this disclosure is a process of acquiring the mapped image A of the first element and the mapped image B of the second element from the cross-section of the battery component. For example, as described later... Figure 4 It is a mapping image of Si elements, which will be discussed later. Figure 5 (a) is a mapping image of the Os element.

[0052] The mapped image can be obtained by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX) measurement of the cross-section of the aforementioned battery component. Preferred measurement conditions include an EDX magnification of 1000x, an accelerating voltage of 5kV, and a measurement time of 60 seconds. Furthermore, the region of the mapped image is preferably 50μm × 50μm or larger. By ensuring the mapped image region is at least a specified size, the correlation coefficient between the first and second elements can be determined with high precision.

[0053] 3. Binarization process

[0054] The binarization process in this disclosure involves binarizing the aforementioned mapped image A and the aforementioned mapped image B respectively to create binarized image a and binarized image b. For example, as described later... Figure 5 (b) is a binarized image of Os elements, obtained by... Figure 5 (a) is obtained by binarizing the mapping image of the Os element shown.

[0055] Methods for creating binarized images include, for example, using image processing libraries such as OpenCV. Furthermore, as a preprocessing step for creating the binarized image, removing noise from the mapped image is preferable. For example, in OpenCV, Gaussian, Median, or Bilateral filters exist for noise removal, but Gaussian is preferred because it can efficiently remove minute noise of about one pixel and has a fast processing speed. Additionally, the binarization threshold is preferably obtained using Otsu's binarization algorithm.

[0056] 4. Calculation process

[0057] The calculation process in this disclosure involves overlaying the binarized image a and the binarized image b to calculate the correlation coefficient between the first element and the second element. For example, as described later... Figure 6 It is a composite image formed by overlaying the binarized images of Si and Os elements.

[0058] The correlation coefficient can be calculated using image processing libraries such as OpenCV, or using well-known image processing software. For example... Figure 3 (a)~ Figure 3 As shown in (c), the Si element is represented by a mesh pattern, and the Os element by a dot pattern. Figure 3 As shown in (a), when the Si and Os elements are completely identical, the correlation coefficient is 1. Furthermore, as... Figure 3 As shown on the right side of (a), regions where neither Si nor Os elements are present are not counted. On the other hand, as... Figure 3 As shown in (b), when the Si and Os elements are completely different, the correlation coefficient becomes -1. Additionally, as... Figure 3 As shown in (c), in half of the entire region, Si and Os elements are consistent, and in the remaining half, only Si or Os elements exist, the correlation coefficient is 0.

[0059] 5. Evaluation methods for battery components

[0060] In the battery component evaluation method disclosed herein, in addition to the first and second elements, a third element can also be evaluated. Specifically, in the image acquisition step, a mapped image C of the third element can be acquired, and in the binarization step, at least one of the following operations can be performed: binarizing the mapped image C to create a binarized image c; in the calculation step, overlapping the binarized image a and the binarized image c to calculate the correlation coefficient between the first and third elements; and overlapping the binarized image b and the binarized image c to calculate the correlation coefficient between the second and third elements.

[0061] The third element is a component different from the first and second elements, preferably a constituent element of the active substance, a constituent element of the solid electrolyte, or a dyeing element used to color the adhesive. For example, the first element may be a constituent element of the active substance, the second element may be a constituent element of the solid electrolyte, and the third element may be a dyeing element used to color the adhesive. In this case, the correlation coefficients between the first element (active substance) and the second element (solid electrolyte), the first element (active substance) and the third element (adhesive), and the second element (solid electrolyte) and the third element (adhesive) can be calculated.

[0062] In the battery component evaluation method disclosed herein, the composition or manufacturing conditions of the battery component can be set based on the obtained correlation coefficient. By manufacturing multiple batteries with varying correlation coefficients according to their composition (e.g., type of material, material ratio), and evaluating the performance of each battery (e.g., capacity, resistance, increase in binding voltage), the allowable range of correlation coefficients can be determined regarding the composition of the battery component. Furthermore, by manufacturing multiple batteries with varying correlation coefficients according to manufacturing conditions (e.g., slurry concentration, type of dispersion medium), and evaluating the performance of each battery, the permissible range of correlation coefficients can be determined regarding the manufacturing conditions. By determining the permissible range of correlation coefficients and using it as a benchmark, setting the composition or manufacturing conditions of the battery component becomes easier.

[0063] Furthermore, this disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and all technical solutions having a structure that is substantially the same as the technical concept described in the claims of this disclosure and performing the same effect are included within the technical scope of this disclosure.

[0064] [Example]

[0065] [Example 1]

[0066] (Preparation of negative electrode active material)

[0067] Metallic Li and Si powders were weighed in a molar ratio of 4:1 and mixed in a mortar under an Ar atmosphere at room temperature for 0.5 hours to induce a reaction, yielding Li₄Si. The obtained Li₄Si was then reacted with ethanol under an Ar atmosphere. The reaction product was considered to contain Si and CH₃CH₂OLi. The reaction product was filtered, and the filtered solid was dried at 120°C for at least 3 hours to obtain porous Si powder.

[0068] Using the obtained porous Si, and with NaH as the Na source, a Na-Si alloy was prepared. Furthermore, NaH that had been pre-washed with hexane was used. NaH and porous Si were weighed at a molar ratio of 1.05:1 and mixed using a shredder. The mixture of NaH and porous Si was heated in a furnace under an Ar atmosphere at 475°C for 40 hours, thereby obtaining a powdered Na-Si alloy.

[0069] Using the obtained Na-Si alloy, and further using AlF3 as a Na scavenger, a solid-state method was employed to generate silicon inclusion compounds. The Na-Si alloy and AlF3 were weighed at a molar ratio of 1:0.35 and mixed using a shredder to obtain the reaction raw materials. The resulting powdered reaction raw materials were placed in a stainless steel reaction vessel and heated in a furnace under an Ar atmosphere at 310°C for 60 hours to react and obtain the precursor active material.

[0070] It was assumed that the obtained precursor active material contained NaF and Al as byproducts. Therefore, the precursor active material was washed with a mixed solvent of HNO3 and H2O at a volume ratio of 10:90. This removed the byproducts from the reaction product. After washing, the mixture was filtered, and the filtered solid was dried at 120°C for at least 3 hours to obtain a negative electrode active material with a crystalline phase containing type II inclusion complexes.

[0071] (Making the negative electrode)

[0072] The obtained negative electrode active material, sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), conductive material (VGCF), tetrahydronaphthalene solution containing binder (BR-based binder) at a ratio of 5% by mass, and tetrahydronaphthalene were added to a polypropylene container and stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was vibrated for 30 minutes using an oscillator (Shibata Scientific Co., Ltd., TTM-1) to obtain a negative electrode slurry. The ratio of negative electrode active material, sulfide solid electrolyte, conductive material, and binder by mass was negative electrode active material: sulfide solid electrolyte: conductive material: binder = 51.27: 42.7: 0.77: 2.89. Furthermore, the solid content concentration of the slurry was 31% by mass. The obtained negative electrode slurry was applied to a negative electrode current collector (Cu foil, UACJ) using a scraper method with a coating tool and dried on a hot plate at 100°C for 30 minutes. Thus, a negative electrode with a negative current collector and a negative electrode layer is obtained.

[0073] (The production of the positive electrode)

[0074] Add positive electrode active material (LiNi) to the polypropylene container 1 / 3 Co 1 / 3 Mn 1 / 3O2, an average particle size of 6 μm, a sulfide solid electrolyte (Li2S-P2S5 system), a conductive material (VGCF), a butyl butyrate solution containing PVDF-based binder at a ratio of 5% by mass, and butyl butyrate were stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was vibrated for 3 minutes using an oscillator (Shibata Scientific Co., Ltd., TTM-1), further stirred for 30 seconds using the ultrasonic dispersion device, and vibrated for 3 minutes to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a positive current collector (Al foil, Showa Denko) using a coating tool via a scraper method, and dried on a hot plate at 100°C for 30 minutes. This yielded a positive electrode having a positive current collector and a positive electrode layer. Furthermore, the area of ​​the positive electrode was smaller than that of the negative electrode.

[0075] (Fabrication of the solid electrolyte layer)

[0076] A sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), a heptane solution containing BR-based binder at a ratio of 5% by mass, and heptane were added to a polypropylene container and stirred for 30 seconds using an ultrasonic dispersion device (SMT UH-50). Next, the container was vibrated for 30 minutes using an oscillator (Shibata Scientific Co., Ltd., TTM-1) to obtain a slurry. The obtained slurry was coated onto a release sheet (Al foil) using a doctor blade method using a coater and dried on a hot plate at 100°C for 30 minutes. This yielded a transfer component having a release sheet and a solid electrolyte layer.

[0077] (The fabrication of an all-solid-state battery)

[0078] A bonding solid electrolyte layer is placed on the positive electrode layer in the positive electrode, and the mixture is pressed in a roll press at 100 kN / cm and 165°C. This yields the first laminate. Next, the negative electrode is placed in a roll press and pressed at 60 kN / cm and 25°C. This yields the pressed negative electrode. Subsequently, a bonding solid electrolyte layer and a transfer member are sequentially placed from the negative electrode layer side. At this time, the bonding solid electrolyte layer and the solid electrolyte layer in the transfer member are arranged opposite each other. The resulting laminate is placed in a planar uniaxial press and pre-pressed at 100 MPa and 25°C for 10 seconds. Then, the release sheet is peeled off from the solid electrolyte layer. This yields the second laminate. Next, the bonding solid electrolyte layer in the first laminate and the solid electrolyte layer in the second laminate are arranged opposite each other and pressed in a planar uniaxial press at 200 MPa and 120°C for 1 minute. This yields an all-solid-state battery.

[0079] [evaluate]

[0080] The cross-section of the negative electrode layer in the all-solid-state battery obtained in Example 1 was processed using a vacuum electronic staining apparatus (VSC4TWDH). Specifically, OsO4-based staining was performed using 5 volume % OsO4 / naphthalene for 5 hours. After staining, SEM-EDX measurements were performed on the cross-section of the negative electrode layer to obtain mapping images of Si and Os elements. The measurement conditions were set to an EDX magnification of 1000x, an accelerating voltage of 5 kV, and a measurement time of 60 seconds. The mapping images focused on areas larger than 50 μm × 50 μm.

[0081] The obtained mapped image is digitized using OpenCV, and noise is removed using a Gaussian filter. Figure 4 This is a mapping image of Si elements. After removing noise from this mapping image, a binarized image is obtained. Additionally, Figure 5 (a) is the mapping image of the Os elements. After removing noise from this mapping image, a binarized image is obtained. Furthermore, Figure 5 (b) is the binarized image of the Os elements. Next, as... Figure 6 As shown, by overlaying the binarized images of Si and Os elements, a composite image for evaluating the correlation coefficient between Si and Os elements is obtained. Furthermore, in... Figure 6 In the image, the areas where Si and Os elements overlap and are clustered together are highlighted.

[0082] Subsequently, the correlation coefficient was calculated using the resulting composite image. Specifically, the correlation coefficient between the Si and Os elements was calculated for each pixel (1280×960) to obtain the overall correlation coefficient of the image. The correlation coefficient was calculated using well-known image processing software. The result showed that the correlation coefficient between the Si and Os elements was 0.076.

Claims

1. An evaluation method for battery components, specifically for battery components containing a first element and a second element, comprising an image acquisition step, a binarization step, and a calculation step. The image acquisition process obtains a mapped image A of the first element and a mapped image B of the second element in the cross-section of the battery component. The binarization process binarizes the mapped image A and the mapped image B respectively, creating binarized image a and binarized image b. The calculation process involves overlapping the binarized image a and the binarized image b and calculating the correlation coefficient between the first element and the second element.

2. The evaluation method for a battery component according to claim 1, wherein the battery component is a positive electrode layer, a negative electrode layer, or a solid electrolyte layer.

3. The evaluation method for battery components according to claim 1, The first element is a constituent element of the active substance. The second element is a constituent element of a solid electrolyte or a dyeing element used to color the adhesive.

4. The evaluation method for battery components according to claim 1, The first element is Si. The second element is an S element, an Os element, or a Ru element.

5. The evaluation method for battery components according to claim 1, In the image acquisition process, the mapped image C of the third element is acquired. In the binarization process, the mapped image C is binarized to create a binarized image c. In the calculation process, at least one of the following is performed: overlapping the binarized image a and the binarized image c and calculating the correlation coefficient of the first element and the third element; and overlapping the binarized image b and the binarized image c and calculating the correlation coefficient of the second element and the third element.

Images