Method for evaluating battery member

Abstract

A main object of the present disclosure is to provide a battery member evaluation method capable of quantitatively evaluating a positional relationship (distribution state) between a first element and a second element.SOLUTION: In the present disclosure, there is provided an evaluation method for a battery member containing a first element and a second element, including a step of obtaining a mapping image A of the first element and a mapping image B of the second element in a cross section of the battery member, a binarization step of binarizing each of the mapping image A and the mapping image B to prepare a binarized image a and a binarized image b, and a superimposing step of superimposing the binarized image a and the binarized image b. A method for evaluating a battery member includes a step of calculating a correlation coefficient between a first element and a second element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating battery components. [Background technology]

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

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-044620 Summary of the Invention [Problem to be solved by the invention]

[0004] Examples of components constituting a battery (battery components) include an electrode layer and an electrolyte layer. The electrode layer may contain a solid electrolyte, a binder, and a conductive material in addition to an active material. The electrolyte layer may contain a solid electrolyte and a binder. When a battery component contains a first element (e.g., an active material) and a second element (e.g., a solid electrolyte or a binder), the positional relationship (distribution state) of the first element and the second element has a significant effect on battery performance.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a method for evaluating a battery component that can quantitatively evaluate the positional relationship (distribution state) of a first element and a second element. [Means for solving the problem]

[0006] [1] A method for evaluating a battery component containing a first element and a second element, comprising: an image acquiring step of acquiring a mapping image A of the first element and a mapping image B of the second element in a cross section of the battery member; a binarization step of binarizing the mapping image A and the mapping image B to generate a binarized image a and a binarized image b, respectively; a calculation step of superimposing the binarized image a and the binarized image b to calculate a correlation coefficient between the first element and the second element; A method for evaluating a battery component, comprising:

[0007] [2] The method for evaluating a battery component according to [1], wherein the battery component is a positive electrode layer, a negative electrode layer, or a solid electrolyte layer.

[0008] [3] the first element is a constituent element of the active material, The method for evaluating a battery component according to [1] or [2], wherein the second element is a constituent element of the solid electrolyte or a dyeing element used to dye a binder.

[0009] [4] the first element is Si, The method for evaluating a battery component according to any one of [1] to [3], wherein the second element is an S element, an Os element, or a Ru element.

[0010] [5] In the image acquisition step, a mapping image C of a third element is acquired, In the binarization step, the mapping image C is binarized to generate a binarized image c; The method for evaluating a battery component according to any one of [1] to [4], wherein in the calculation step, at least one of the following is performed: superimposing the binarized image a and the binarized image c to calculate a correlation coefficient between the first element and the third element; and superimposing the binarized image b and the binarized image c to calculate a correlation coefficient between the second element and the third element. [Effects of the Invention]

[0011] The method for evaluating a battery component according to the present disclosure has the effect of being able to quantitatively evaluate the positional relationship (distribution state) of the first element and the second element. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a battery. [Figure 2] FIG. 1 is a flow diagram illustrating a method for evaluating battery components according to the present disclosure. [Figure 3] 1 is an image illustrating the correlation coefficient of Si and Os. [Figure 4] This is a mapping image of Si. [Figure 5] The mapping image and binarized image of Os are shown. [Figure 6] This is an image obtained by superimposing a binarized image of Si and a binarized image of Os. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, the method for evaluating battery components and the method for setting manufacturing conditions for battery components according to the present disclosure will be described in detail.

[0014] A. Evaluation method for battery components FIG. 1 is a schematic cross-sectional view illustrating an example battery. The battery 10 shown in FIG. 1 includes 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 electrode current collector 4 that collects current from the positive electrode layer 1, and a negative electrode current collector 5 that collects current from the negative electrode layer 2. In this disclosure, the battery components refer to the components that constitute the battery 10. In this disclosure, the battery components to be evaluated may be any of the positive electrode layer 1, the negative electrode layer 2, the electrolyte layer 3, the positive electrode current collector 4, and the negative electrode current collector 5, but are preferably the positive electrode layer 1, the negative electrode layer 2, or the electrolyte layer 3. The battery components contain a first element (e.g., an active material) and a second element (e.g., a solid electrolyte or a binder).

[0015] Fig. 2 is a flow diagram illustrating a method for evaluating a battery component according to the present disclosure. As shown in Fig. 2, in the method for evaluating a battery component according to the present disclosure, first, a mapping image A of a first element and a mapping image B of a second element are obtained in a cross section of the battery component (image obtaining step). Next, mapping image A and mapping image B are binarized to produce binarized images a and b, respectively (binarization step). Next, binarized image a and binarized image b are superimposed to calculate the correlation coefficient between the first element and the second element (calculation step).

[0016] According to the present disclosure, the positional relationship (distribution state) between the first element and the second element can be quantitatively evaluated by calculating the correlation coefficient between the first element and the second element. As described above, when a battery component contains a first element (e.g., an active material) and a second element (e.g., a solid electrolyte or a binder), the positional relationship (distribution state) between the first element and the second element has a significant effect on battery performance.

[0017] For example, in the case of an active material that undergoes a large volume change during charge and discharge, such as a Si-based active material, it may be possible to suppress the volume change during charge and discharge by increasing the amount of binder disposed around the active material. Conventionally, there has been no index for quantitatively evaluating the distribution of a second element (binder) relative to a first element (active material). In contrast, in the present disclosure, the positional relationship (distribution state) between the first element (active material) and the second element (binder) can be quantitatively evaluated by calculating the correlation coefficient between the first element (active material) and the second element (binder).

[0018] Furthermore, to create a good ion conduction path, it is necessary for the solid electrolyte to be appropriately arranged around the active material. Conventionally, there has been no index for quantitatively evaluating the distribution of a second element (solid electrolyte) relative to a first element (active material). In contrast, in the present disclosure, the positional relationship (distribution state) between the first element (active material) and the second element (solid electrolyte) can be quantitatively evaluated by calculating the correlation coefficient between the first element (active material) and the second element (solid electrolyte).

[0019] 1. Battery components The battery components in this disclosure are components that constitute a battery. The battery may be a liquid-based battery or a solid-state battery. The battery components to be evaluated may be, for example, any of the positive electrode layer 1, the negative electrode layer 2, the electrolyte layer 3, the positive electrode current collector 4, and the negative electrode current collector 5 shown in FIG. 1 , but are preferably the positive electrode layer 1, the negative electrode layer 2, or the electrolyte layer 3.

[0020] 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 the positive electrode active material include LiCoO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, etc., rock salt layered active materials, LiMn2O4, Li(Ni 0.5 Mn 1.5Examples of the positive electrode active material include spinel-type active materials such as LiFePO4 and olivine-type active materials such as LiFePO4. Sulfur (S) may also be used as the positive electrode active material.

[0021] Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complex hydride solid electrolytes. The sulfide solid electrolyte preferably contains Li, Me (Me is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may also contain halogen elements such as F, Cl, Br, and I.

[0022] Examples of binders 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 binder contains an unsaturated bond, the unsaturated bond reacts with OsO4 (osmium oxide), thereby dyeing the binder. RuO4 (ruthenium oxide) may be used instead of OsO4. Examples of conductive materials include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0023] 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 the negative electrode active material include a Si-based active material and lithium titanate. Examples of the Si-based active material include simple Si, a Si alloy, a Si oxide, and a Si carbide. The Si-based active material may be porous. Examples of the lithium titanate include Li4Ti5O 12The solid electrolyte, binder, and conductive material used in the negative electrode layer are the same as those described above. 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 those described above.

[0024] 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 dye element that dyes the binder, and is particularly preferably a constituent element of the active material. For example, when the active material is a Si-based active material, the first element is preferably Si, which is a constituent element of the Si-based active material. On the other hand, when the solid electrolyte is a sulfide solid electrolyte, the first element may be S, which is a constituent element of the sulfide solid electrolyte. Furthermore, when the binder has an unsaturated bond, the first element may be a dye element that dyes the binder (e.g., Os or Ru). On the other hand, the second element is a component different from the first element and is preferably a constituent element of the active material, a constituent element of the solid electrolyte, or a dye element that dyes the binder, and is particularly preferably a constituent element of the solid electrolyte or a dye element that dyes the binder. These elements are the same as those described above.

[0025] 2. Image acquisition process The image acquisition step in the present disclosure is a step of acquiring a mapping image A of the first element and a mapping image B of the second element in a cross section of the battery component. For example, Fig. 4 (described later) is a mapping image of Si element, and Fig. 5(a) (described later) is a mapping image of Os element.

[0026] The mapping image can be obtained by performing scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX) on the cross section of the battery component. The measurement conditions are preferably, for example, an EDX magnification of 1000x, an acceleration voltage of 5 kV, and a measurement time of 60 seconds. The area of ​​the mapping image is preferably 50 μm × 50 μm or more. By making the area of ​​the mapping image larger than a predetermined size, the correlation coefficient between the first element and the second element can be determined with high accuracy.

[0027] 3.Binarization process The binarization step in the present disclosure is a step of binarizing the mapping image A and the mapping image B, respectively, to produce binarized images a and b. For example, Fig. 5(b), which will be described later, is a binarized image of the Os element, and is obtained by binarizing the mapping image of the Os element shown in Fig. 5(a).

[0028] Examples of methods for creating a binarized image include a method using an image processing library such as OpenCV. Furthermore, as a preprocessing step for creating a binarized image, it is preferable to remove noise from the mapping image. For example, OpenCV provides Gaussian, Median, and Bilateral filters for noise removal, but it is preferable to use Gaussian because it can efficiently remove minute noise of about one pixel and has a fast processing speed. Furthermore, it is preferable to determine the binarization threshold using Otsu's binarization.

[0029] 4.Calculation process The calculation step in the present disclosure is a step of calculating the correlation coefficient between the first element and the second element by superimposing the binarized image a and the binarized image b. For example, Fig. 6, which will be described later, is a composite image obtained by superimposing a binarized image of Si element and a binarized image of Os element.

[0030] The correlation coefficient may be calculated using an image processing library such as OpenCV or known image processing software. As shown in FIGS. 3(a) to 3(c), Si elements are represented by a mesh pattern, and Os elements are represented by a dot pattern. As shown in FIG. 3(a), when Si elements and Os elements are perfectly matched, the correlation coefficient is 1. Note that, as shown on the right side of FIG. 3(a), regions where neither Si elements nor Os elements are present are not counted. On the other hand, as shown in FIG. 3(b), when Si elements and Os elements are not perfectly matched, the correlation coefficient is -1. Furthermore, as shown in FIG. 3(c), when Si elements and Os elements are perfectly matched in half of the entire region and only Si elements or only Os elements are present in the remaining half, the correlation coefficient is 0.

[0031] 5. Evaluation method for battery components In the evaluation method for battery components according to the present disclosure, a third element may be evaluated in addition to the first and second elements. Specifically, the method may include acquiring a mapping image C of the third element in the image acquisition step, binarizing the mapping image C to produce a binarized image c in the binarization step, and overlaying the binarized image a and the binarized image c in the calculation step to calculate a correlation coefficient between the first element and the third element, or overlaying the binarized image b and the binarized image c to calculate a correlation coefficient between the second element and the third element.

[0032] The third element is a component different from the first and second elements, and is preferably a constituent element of the active material, a constituent element of the solid electrolyte, or a dye element that dyes the binder. For example, the first element may be a constituent element of the active material, the second element may be a constituent element of the solid electrolyte, and the third element may be a dye element that dyes the binder. In this case, the correlation coefficient between the first element (active material) and the second element (solid electrolyte), the correlation coefficient between the first element (active material) and the third element (binder), and the correlation coefficient between the second element (solid electrolyte) and the third element (binder) can be calculated.

[0033] In the battery component evaluation method disclosed herein, the composition or manufacturing conditions of the battery components can be set based on the obtained correlation coefficient. By fabricating multiple batteries with different correlation coefficients depending on the composition (e.g., type of material, ratio of materials) and evaluating the performance of each battery (e.g., capacity, resistance, confining pressure increase), it is possible to identify an acceptable range of correlation coefficients for the composition of the battery components. Furthermore, by fabricating multiple batteries with different correlation coefficients depending on the manufacturing conditions (e.g., slurry concentration, type of dispersion medium) and evaluating the performance of each battery, it is possible to identify an acceptable range of correlation coefficients for the manufacturing conditions. Identifying the acceptable range of correlation coefficients and using it as a standard facilitates the setting of the composition or manufacturing conditions of the battery components.

[0034] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0035] [Example 1] (Preparation of negative electrode active material) Metallic Li and Si powder were weighed out in a molar ratio of 4:1 and mixed in a mortar under an Ar atmosphere at room temperature for 0.5 hours to react. This produced Li4Si. The resulting Li4Si was then reacted with ethanol under an Ar atmosphere. The resulting reaction product is believed to contain Si and CH3CHOLi. The reaction product was filtered, and the filtered solid was dried at 120°C for at least 3 hours to produce powdered porous Si.

[0036] The obtained porous Si was used to produce a Na-Si alloy using NaH as a Na source. The NaH used was previously washed with hexane. NaH and porous Si were weighed out to a molar ratio of 1.05:1 and mixed using a cutter mill. The mixture of NaH and porous Si was heated in a heating furnace under an Ar atmosphere at 475°C for 40 hours to obtain a powdered Na-Si alloy.

[0037] Using the obtained Na-Si alloy and AlF3 as a Na trapping agent, silicon clathrate was produced by solid-phase method. The Na-Si alloy and AlF3 were weighed out to a molar ratio of 1:0.35 and mixed using a cutter mill to obtain a reaction material. The obtained powdered reaction material was placed in a stainless steel reaction vessel and heated in a heating furnace under an Ar atmosphere at 310°C for 60 hours to react, obtaining a precursor active material.

[0038] The precursor active material thus obtained is believed to contain NaF and Al as by-products. Therefore, the precursor active material was washed with a mixed solvent of HNO3 and HO in a volume ratio of 10:90. This removed the by-products 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 clathrate II crystalline phase.

[0039] (Preparation of negative electrode) The resulting negative electrode active material, sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), conductive material (VGCF), and tetralin solution containing 5% by mass of binder (BR-based binder) were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to obtain a negative electrode slurry. The mass ratio of the negative electrode active material, sulfide solid electrolyte, conductive material, and binder was negative electrode active material:sulfide solid electrolyte:conductive material:binder = 51.27:42.7:0.77:2.89. The solids concentration of the slurry was 31% by mass. The obtained negative electrode slurry was applied onto a negative electrode current collector (Cu foil, manufactured by UACJ) by a blade method using an applicator, and then dried for 30 minutes on a hot plate at 100°C, thereby obtaining a negative electrode having a negative electrode current collector and a negative electrode layer.

[0040] (Preparation of positive electrode) The positive electrode active material (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A butyl butyrate solution containing 5% by mass of 02 (average particle size 6 μm), a sulfide solid electrolyte (Li2S-P2S5 system), a conductive material (VGCF), and a PVDF-based binder was added, and the solution was stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 3 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.), followed by another 30 seconds of stirring using the ultrasonic disperser and another 3 minutes of shaking using the shaker to obtain a positive electrode slurry. The resulting positive electrode slurry was applied to a positive electrode current collector (Al foil, manufactured by Showa Denko KK) using an applicator by the blade method and dried for 30 minutes on a hot plate at 100 °C. This resulted in a positive electrode comprising a positive electrode current collector and a positive electrode layer. The area of ​​the positive electrode was smaller than that of the negative electrode.

[0041] (Fabrication of solid electrolyte layer) A sulfide solid electrolyte (Li2S-P2S5-based glass ceramic), a heptane solution containing 5% by mass of a BR-based binder, and heptane were added to a polypropylene container and stirred for 30 seconds using an ultrasonic disperser (UH-50, manufactured by SMT). The container was then shaken for 30 minutes using a shaker (TTM-1, manufactured by Shibata Scientific Co., Ltd.) to obtain a slurry. The resulting slurry was applied to a release sheet (Al foil) using an applicator by the blade method and dried on a hot plate at 100°C for 30 minutes. This resulted in a transfer member having a release sheet and a solid electrolyte layer.

[0042] (Fabrication of all-solid-state batteries) A bonding solid electrolyte layer was placed on the positive electrode layer of the positive electrode, set in a roll press, and pressed at 100 kN / cm and 165°C. This resulted in a first laminate. Next, the negative electrode was set in the roll press and pressed at 60 kN / cm and 25°C. This resulted in a pressed negative electrode. Then, a bonding solid electrolyte layer and a transfer member were placed in order from the negative electrode layer side. At this time, the bonding solid electrolyte layer and the solid electrolyte layer on the transfer member were placed facing each other. The resulting laminate was set in a flat uniaxial press and temporarily pressed at 100 MPa and 25°C for 10 seconds. Then, the release sheet was peeled off from the solid electrolyte layer. This resulted in a second laminate. Next, the bonding solid electrolyte layer of the first laminate and the solid electrolyte layer of the second laminate were placed facing each other, set in a flat uniaxial press, and pressed at 200 MPa and 120°C for 1 minute. This resulted in an all-solid-state battery.

[0043] [evaluation] The cross section of the negative electrode layer in the all-solid-state battery obtained in Example 1 was processed, and the cross section of the negative electrode layer was stained using a vacuum electron staining device (VSC4TWDH). Specifically, the cross section was treated with 5 vol% OsO4 / naphthalene for 5 hours, and stained with OsO4. After staining, SEM-EDX measurement was performed on the cross section of the negative electrode layer, and mapping images of Si element and Os element were obtained. The measurement conditions were an EDX magnification of 1000x, an acceleration voltage of 5 kV, and a measurement time of 60 seconds. The mapping image was taken of an area of ​​50 μm × 50 μm or more.

[0044] The obtained mapping image was digitized using OpenCV and noise was removed using a Gaussian filter. Figure 4 shows a mapping image of Si element; noise was removed from this mapping image, and then a binarized image was obtained. Figure 5(a) shows a mapping image of Os element; noise was removed from this mapping image, and then a binarized image was obtained. Figure 5(b) shows a binarized image of Os element. Next, as shown in Figure 6, the binarized image of Si element and the binarized image of Os element were overlaid to obtain a composite image for evaluating the correlation coefficient between Si element and Os element. Note that in Figure 6, areas where Si element and Os element are highly concentrated are displayed brightly.

[0045] The correlation coefficient was then calculated using the resulting composite image. Specifically, the correlation coefficient between the Si element and the Os element was calculated for each pixel (1280 x 960), and the correlation coefficient for the entire image was determined. The correlation coefficient was calculated using known image processing software. As a result, the correlation coefficient between the Si element and the Os element was 0.076. [Explanation of symbols]

[0046] 1...Positive electrode layer 2...Anode layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...battery

Claims

1. A method for evaluating a battery component containing a first element and a second element, comprising: an image acquiring step of acquiring a mapping image A of the first element and a mapping image B of the second element in a cross section of the battery member; a binarization step of binarizing the mapping image A and the mapping image B to generate a binarized image a and a binarized image b, respectively; a calculation step of calculating a correlation coefficient between the first element and the second element by superimposing the binarized image a and the binarized image b; A method for evaluating a battery component, comprising:

2. The method for evaluating 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 first element is a constituent element of the active material, The method for evaluating a battery component according to claim 1 , wherein the second element is a constituent element of a solid electrolyte or a dye element obtained by dyeing a binder.

4. the first element is a Si element, The method for evaluating a battery component according to claim 1 , wherein the second element is an S element, an Os element, or a Ru element.

5. In the image acquisition step, a mapping image C of a third element is acquired, In the binarization step, the mapping image C is binarized to generate a binarized image c; 2. The method for evaluating a battery component according to claim 1, wherein in the calculation step, at least one of the following is performed: superimposing the binarized image a and the binarized image c to calculate a correlation coefficient between the first element and the third element; and superimposing the binarized image b and the binarized image c to calculate a correlation coefficient between the second element and the third element.

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