Method for evaluating nonaqueous secondary battery electrode, method for producing nonaqueous secondary battery electrode, device for supporting selection of nonaqueous secondary battery electrode material, and program

Abstract

To provide an evaluation method of a nonaqueous secondary battery electrode, a manufacturing method of manufacturing the nonaqueous secondary battery electrode having low internal resistance from an obtained evaluation result, a material selection support device for supporting selection of a material of the nonaqueous secondary battery electrode having low internal resistance based on the obtained evaluation result, and a program.SOLUTION: A method for evaluating a non-aqueous secondary battery electrode includes a step of acquiring a three dimensional image of a non-aqueous secondary battery electrode that includes an active material layer containing an active material and a binder on a current collector, and a step of visualizing pores of the active material layer in the three dimensional image and analyzing a number per unit area of through-channels that penetrate from one surface to another surface of the active material layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating non-aqueous secondary battery electrodes, a method for manufacturing non-aqueous secondary battery electrodes, and a device and program for supporting the selection of electrode materials for non-aqueous secondary batteries. [Background technology]

[0002] A nonaqueous secondary battery has a configuration including, for example, a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolyte. A nonaqueous secondary battery is a secondary battery in which ions move between the positive electrode and the negative electrode to charge and discharge the battery. Therefore, in nonaqueous secondary batteries, it is required to reduce the internal resistance of the electrodes and increase the diffusibility of ions within the electrodes. A typical example of a nonaqueous secondary battery is a lithium-ion secondary battery.

[0003] Non-aqueous secondary batteries are used as power sources for notebook computers, mobile phones, power tools, electronic devices, communication devices, etc., due to their compact size and lightweight design. Recently, they have also been used in electric vehicles and hybrid vehicles, due to their application to environmentally friendly vehicles.

[0004] A commonly used electrode for non-aqueous secondary batteries is one in which an active material layer is formed on a metal current collector. The active material layer contains an active material, a binder, and, if necessary, a conductive additive. The active material is a substance capable of inserting and extracting ions that serve as charge carriers. The binder serves to bind active materials together and to bind the active material to the current collector.

[0005] For example, Patent Document 1 describes a binder resin composition for electrodes of non-aqueous electrolyte energy devices, which comprises: (a) a binder resin capable of binding an active material for electrodes of non-aqueous electrolyte energy devices; and (b) a mixed solvent of a good solvent for the binder resin, which has a boiling point lower than that of a poor solvent, and a poor solvent for the binder resin. The binder resin composition of Patent Document 1 uses a mixed solvent consisting of a good solvent that dissolves the polymer and a poor solvent that does not dissolve the polymer as the solvent for dissolving the binder polymer, and therefore the active material surface is bound without being covered with the binder resin, which is explained to reduce the internal resistance of the electrode. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-134492 Summary of the Invention [Problem to be solved by the invention]

[0007] However, no evaluation method has been established that conceptualizes the ease of ion diffusion within electrodes of non-aqueous secondary batteries and correlates it with the internal resistance of the electrodes. Therefore, this disclosure provides a method for evaluating nonaqueous secondary battery electrodes that conceptualizes the ease of ion diffusion within the electrode to determine the electrode's internal resistance. It also provides a method for manufacturing nonaqueous secondary battery electrodes with low internal resistance based on the evaluation results. Furthermore, it provides a material selection support device and program that support the selection of materials for nonaqueous secondary battery electrodes with low internal resistance based on the evaluation results. [Means for solving the problem]

[0008] The present disclosure includes the following aspects. <1> obtaining a three-dimensional image of a non-aqueous secondary battery electrode having an active material layer containing an active material and a binder on a current collector; a step of visualizing the pores of the active material layer in the three-dimensional image and analyzing the number of through-flow paths per unit area that penetrate from one surface to the other surface of the active material layer; A method for evaluating a non-aqueous secondary battery electrode, comprising: <2> The through-flow path further includes a step of calculating a tortuosity represented by the following formula (1), <1> The method for evaluating a non-aqueous secondary battery electrode according to claim 1. T=f / s (1) (In formula (1), T is the tortuosity, f is the total length of the through-flow passage, and s is the distance of a straight line from the opening of the through-flow passage on one surface of the active material layer to the opening of the through-flow passage on the other surface.) <3> a step of visualizing pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detecting the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; predicting the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; determining a composition of the active material layer such that the predicted number of through-flow paths per unit area is equal to or greater than a predetermined value; forming an active material layer having the determined composition on a current collector; A method for producing a non-aqueous secondary battery electrode, comprising: <4> a detection unit that visualizes pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; a prediction unit that predicts the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; a composition determination unit that determines a composition of the active material layer that will result in a predicted number of through-flow paths per unit area of ​​equal to or greater than a predetermined value; A selection support device for electrode materials for non-aqueous secondary batteries, comprising: <5> Computer, a detection unit that visualizes pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; a prediction unit that predicts the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; and a composition determination unit that determines a composition of the active material layer that will result in a predicted number of through-flow paths per unit area of ​​at least a predetermined value; A program to function as a [Effects of the Invention]

[0009] According to the present disclosure, a method for evaluating nonaqueous secondary battery electrodes that conceptualizes the ease of ion diffusion within the electrode and determines the internal resistance of the electrode can be provided. Furthermore, a method for manufacturing nonaqueous secondary battery electrodes with low internal resistance based on the obtained evaluation results can be provided. Furthermore, a material selection support device and a program can be provided that support the selection of materials for nonaqueous secondary battery electrodes with low internal resistance based on the obtained evaluation results. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows X-ray CT images in which pores in the active material layers of Examples 1 and 4 are colored. [Figure 2] 1 shows scanning electron microscope (SEM) photographs of the surfaces of active material layers in Examples 1 and 4 of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing the pore structure of an active material layer. [Figure 4] FIG. 2 is a diagram showing an example of one flow path (central axis) in a thinned view of a cross section in the thickness direction (x-axis direction) of an active material layer. [Figure 5] FIG. 10 is a diagram showing another example of a flow path (central axis) in a thinned view of a cross section in the thickness direction (x-axis direction) of an active material layer. [Figure 6]FIG. 10 is a diagram for explaining how to calculate the curvature ratio of a branched route in a thinned diagram. [Figure 7] 10 is an example of a colored image. [Figure 8] 10 shows an example of a colored image when the binder type is changed. [Figure 9] FIG. 2 is a block diagram showing an example of a functional configuration of the material selection assisting device. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, as embodiments of the present disclosure, a method for evaluating non-aqueous secondary battery electrodes, a method for manufacturing non-aqueous secondary battery electrodes, an apparatus for supporting selection of non-aqueous secondary battery electrode materials, and a program will be described. Note that the present disclosure is not limited to the embodiments described below. In the following embodiments, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. In the present disclosure, each component may contain multiple substances corresponding to the component. When multiple substances corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where the layer is formed over the entire area when the area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area.

[0012] <Evaluation method for non-aqueous secondary battery electrodes> The method for evaluating a nonaqueous secondary battery electrode according to the present disclosure includes the steps of: acquiring a three-dimensional image of a nonaqueous secondary battery electrode having an active material layer containing an active material and a binder on a current collector; and visualizing pores in the active material layer in the three-dimensional image and analyzing the number of through-flow paths per unit area that penetrate from one surface to the other surface of the active material layer. Hereinafter, the term "nonaqueous secondary battery electrode" may be abbreviated as "electrode." Furthermore, the "number of through-flow paths per unit area that penetrate from one surface to the other surface of the active material layer" may also be referred to as the "number of through-flow paths." In the present disclosure, one surface of the active material layer is the outer surface opposite the current collector side into which the electrolyte solution penetrates, and the other surface of the active material layer is the surface on the current collector side.

[0013] According to the evaluation method configured as above, the ease of ion diffusion within the electrode can be conceptualized to determine the internal resistance of the electrode. The reason for this is presumed to be as follows. In the process of manufacturing electrodes for non-aqueous secondary batteries, a slurry (electrode slurry) in which a binder, active material, etc. are dissolved or dispersed in a solvent is applied to the surface of a current collector, dried, and, if necessary, compressed and molded using a roll press or the like to form an active material layer on the current collector. The active material layer obtained through this process has a complex structure, making it difficult to correlate it with the internal resistance of the battery.

[0014] In this context, it has been found that the ease of ion diffusion within an electrode is related to the number of through-flow paths per unit area of ​​the active material layer. Pores in the active material layer exist not only as through-flow paths that penetrate from one side of the active material layer to the other, but also as paths that terminate midway from one side of the active material layer, and as independent pores that do not open to the surface of the active material layer. The method for evaluating nonaqueous secondary battery electrodes disclosed herein focuses on through-flow paths among these pores and further analyzes the number of through-flow paths per unit area. It has been found that this makes it possible to determine the internal resistance of an electrode regardless of the specific composition of the active material layer. The evaluation method of the present disclosure can be applied to non-aqueous secondary battery electrodes, and may be applied to either positive or negative electrodes, with negative electrodes being preferred.

[0015] Each step of the method for evaluating a nonaqueous secondary battery electrode according to the present disclosure will be described below. Note that the "step of acquiring a three-dimensional image of a nonaqueous secondary battery electrode having an active material layer containing an active material and a binder on a current collector" will also be referred to as the "step of acquiring a three-dimensional image," and the "step of visualizing the pores in the active material layer in the three-dimensional image and analyzing the number of through-flow paths per unit area that penetrate from one surface of the active material layer to the other surface of the active material layer" will also be referred to as the "step of analyzing." The evaluation method of the present disclosure may further include other steps.

[0016] (3D image acquisition process) In the method for evaluating a nonaqueous secondary battery electrode according to the present disclosure, a three-dimensional image of a nonaqueous secondary battery electrode having an active material layer containing an active material and a binder on a current collector is first obtained. The three-dimensional image may be obtained for only the active material layer. The current collector, active material and binder may be selected from those used in the relevant fields.

[0017] For example, the current collector is preferably made of a metal, and preferably contains a metal such as iron, copper, aluminum, nickel, or stainless steel as a main component. When the nonaqueous secondary battery electrode is a negative electrode of a lithium-ion secondary battery, the current collector preferably contains copper as a main component. The phrase "containing metal A as a main component" includes cases where unavoidable impurities are contained in addition to metal A, cases where two or more metals including metal A are used in combination and metal A accounts for the largest proportion by mass, and cases where metal A accounts for the largest proportion by mass in an alloy of two or more metals including metal A. The thickness of the current collector is preferably 0.001 mm to 0.5 mm. The current collector may be a metal sheet.

[0018] The active material is a material capable of intercalating / deintercalating ions that serve as charge carriers, such as lithium ions. The ions that serve as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions.

[0019] When the electrode is a negative electrode, the active material, i.e., the negative electrode active material, preferably contains at least one selected from the group consisting of carbon materials, silicon-containing materials, and titanium-containing materials. Examples of carbon materials used as the active material include cokes such as petroleum coke, pitch coke, and coal coke; carbonized organic polymers; and graphites such as artificial graphite and natural graphite. Examples of silicon-containing materials include silicon itself and silicon compounds such as silicon oxide. Examples of titanium-containing materials include lithium titanate. These materials may be used alone, in combination of two or more types, or in a composite of two or more types.

[0020] The negative electrode active material preferably contains at least one selected from the group consisting of a carbon material and a silicon-containing material, more preferably contains a carbon material, particularly preferably contains graphite, and most preferably contains artificial graphite, because the effects of the present disclosure are particularly enhanced when the negative electrode active material contains these materials.

[0021] The negative electrode active material preferably contains 50% by mass or more of graphite, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0022] When the electrode is a positive electrode, the active material, i.e., the positive electrode active material, is a material with a more noble standard electrode potential than the negative electrode active material. Examples of positive electrode active materials include nickel-containing lithium composite oxides such as Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides; lithium cobalt oxide (LiCoO); spinel-type lithium manganese oxide (LiMnO); olivine-type lithium iron phosphate; chalcogen compounds such as TiS; and transition metal oxides such as MnO, MoO, and VO. These materials may be used alone or in combination as the positive electrode active material.

[0023] Preferred examples of the binder include, but are not limited to, aromatic ethylenically unsaturated compounds, nonionic (meth)acrylic acid esters, and copolymers with anionic unsaturated compounds. The binder may have a crosslinked structure. The particles formed by the binder may contain a surfactant or the like.

[0024] The aromatic ethylenically unsaturated compound is a nonionic aromatic compound having an ethylenically unsaturated bond. Hereinafter, unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability. Examples of the aromatic ethylenically unsaturated compound include styrene, t-butylstyrene, p-methylstyrene, and benzyl (meth)acrylate.

[0025] The nonionic (meth)acrylic acid ester is preferably a nonionic aliphatic compound having one (meth)acryloyl group. Examples of the (meth)acrylic acid alkyl ester include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. The (meth)acrylic acid alkyl ester may have a hydroxy group. Examples of nonionic (meth)acrylic acid esters having a hydroxy group include, but are not limited to, hydroxymethyl (meth)acrylate and 2-hydroxyethyl (meth)acrylate.

[0026] Anionic unsaturated compounds are compounds having anionic functional groups. Examples of the anionic functional groups include carboxyl groups, sulfo groups, and phosphate groups. The anionic functional groups may form salts. Examples of anionic unsaturated compounds include, but are not limited to, acrylic acid, itaconic acid, and sodium p-styrenesulfonate.

[0027] When the binder has a crosslinked structure, it may be a polymer polymerized using a monomer having a crosslinkable functional group, such as, but not limited to, divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate.

[0028] The binder may be a polymer polymerized using a polymerizable surfactant, which is a compound that has an ethylenically unsaturated bond and functions as a surfactant.

[0029] Examples of methods for producing a non-aqueous secondary battery electrode having an active material layer containing an active material and a binder on a current collector include a method in which an electrode slurry containing an active material and a solvent or dispersion medium is applied to a current collector and dried to form an active material layer.

[0030] The solvent or dispersion medium is preferably an aqueous medium. The aqueous medium is preferably at least one selected from the group consisting of water and hydrophilic solvents. The hydrophilic solvent may be used alone or in combination of two or more. Examples of the hydrophilic solvent include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium is preferably water. A mixture of water and a hydrophilic solvent may also be used as the aqueous medium.

[0031] The electrode slurry contains a binder, an active material, and a solvent or dispersion medium, and may contain other components such as a conductive aid, a surfactant having no ethylenically unsaturated bond, and other additives.

[0032] The contents of the binder, active material, solvent or dispersion medium, and other components in the electrode slurry are adjusted as appropriate.

[0033] The method for applying the electrode slurry to the current collector is not particularly limited, and examples thereof include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dipping method, and squeeze method. Among these, in consideration of the physical properties such as viscosity of the electrode slurry and drying property, the doctor blade method, knife method, or extrusion method is preferably used. When these application methods are used, an active material layer having a smooth surface and small thickness variation tends to be obtained.

[0034] The electrode slurry may be applied to only one side of the current collector or to both sides. When the electrode slurry is applied to both sides of the current collector, it may be applied to each side sequentially or to both sides at once. Furthermore, the electrode slurry may be applied to the current collector continuously or intermittently. The amount of electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the electrode slurry, etc. The amount of electrode slurry to be applied depends on the properties of the electrode slurry, but is generally 25 mg / cm 2 It is preferable that the amount of the electrode slurry applied to each surface is less than or equal to 100% by weight (when applied to both surfaces, the amount applied to each surface) because this can prevent cracks from occurring on the electrode surface during the drying process of the electrode slurry.

[0035] The electrode slurry applied to the current collector is dried to form an active material layer on the current collector. The method for drying the electrode slurry is not particularly limited, and examples thereof include hot air, reduced pressure or vacuum environment, (far) infrared rays, and low-temperature air, which may be used alone or in combination of two or more.

[0036] The electrode sheet in which the active material layer is formed on the current collector may be cut to a size and shape appropriate for the electrode. The method for cutting the electrode sheet is not particularly limited, and slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like may be used.

[0037] Before or after cutting the electrode sheet, the electrode sheet may be pressed as needed. Pressing allows the active material to be more firmly attached to the current collector, further thinning the electrode, thereby enabling the nonaqueous battery to be miniaturized. As a pressing method, a general method can be used, and a mold pressing method or a roll pressing method is preferably used.

[0038] The thickness of the active material layer formed is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. When the thickness of the active material layer is within the above range, the charge / discharge capacity of the nonaqueous secondary battery tends to be improved. The thickness of the active material layer is preferably 200 μm or less, more preferably 170 μm or less, and even more preferably 150 μm or less. When the thickness of the active material layer is within this range, the electrode resistance of the non-aqueous secondary battery tends to be reduced.

[0039] The thickness of the active material layer is measured with a micrometer and is defined as the arithmetic mean of measurements taken at three arbitrarily selected points. When the active material layer is provided on both sides of the current collector, the thickness of the active material layer is the thickness per side.

[0040] The non-aqueous secondary battery electrode used in the electrode evaluation method of the present disclosure may be one produced by the method described above, or may be a commercially available product. There are no particular limitations on the method for obtaining a 3D image of the electrode, and examples include methods using X-ray CT, FIB-SEM, electron tomography, etc. By observing the sample using these methods, a 3D image of the pores in the electrode can be obtained, and information on the connections of the pores, i.e., the shape, length, number, etc. of the flow channels, which cannot be obtained by cross-sectional observation, can be obtained.

[0041] In X-ray CT, an object is irradiated with X-rays, and an image is obtained by utilizing the fact that some of the irradiated X-rays are absorbed by the object and the rest are transmitted. The structure of the material, including its internal structure, may be visualized by rotating the object to be observed, photographing it with X-rays from various angles, and then converting the resulting cross-sectional images into three dimensions using computer processing. The degree of X-ray absorption varies depending on the type and amount of elements contained in the object, and information on the element distribution inside the object can be obtained from this variation.

[0042] (Analysis process) Next, the pores in the active material layer in the three-dimensional image obtained above are visualized, and the number of through-flow paths per unit area that penetrate from one surface to the other surface of the active material layer is analyzed.

[0043] Figure 1 shows X-ray CT images of the surfaces of the active material layers in Examples 1 and 4. The X-ray CT images in Figure 1 are colored images in which pores (through-flow paths) extending from the surface to a depth of 50 µm are colored. 2 also shows scanning electron microscope (SEM) photographs of the surfaces of the active material layers of Examples 1 and 4. However, the SEM photographs in FIG. 2 were taken at a different location than the X-ray CT image in FIG.

[0044] The visualization may be performed by thinning the image based on the binarized image data. Examples of methods for binarizing and thinning a three-dimensional image include methods using known image processing software.

[0045] Below is an example of thinning a 3D image. Figure 3 is a schematic diagram showing the pore structure of an electrode. Thinning is performed by binarizing a three-dimensional image of the electrode and then generating a medial axis 3 that continuously connects the centers of the pores. The thin wire terminates when the central axes of the multiple spaces 5a-5d partitioned by the narrowed portions 4 (portions with reduced cross-sectional areas) of the pores are continuously connected and the flow path is completely closed by the narrowed portions 4. Therefore, the central axis 3 is the axis that remains as a result of the narrowing of the pores.

[0046] The electrode evaluation method of the present disclosure may include a step of obtaining an image represented by the central axes of the pores by thinning the pores. In the present disclosure, an image represented by the central axes of the holes, i.e., an image of the thinned holes, is also referred to as a “thinned image.” A thinned image is an image that visualizes the three-dimensional pore structure (channel structure).

[0047] When the central axis 3 penetrates from one surface of the active material layer to the other, it becomes a through-flow path. The number of central axes 3 that become through-flow paths per unit area on one surface of the active material layer (the surface on the electrolyte inlet side) is counted. The number of through-flow paths may be determined using three-dimensional image analysis software. Examples of three-dimensional image analysis software include ExFact VR and ExFact Analysis for Porous Particles, manufactured by Nippon Visual Science Co., Ltd.

[0048] Furthermore, as shown in Figure 1, the method may include a step of obtaining an image in which the through-channels are colored after thinning the three-dimensional image. A method for coloring the through-channels may include, for example, a method using known image processing software. In the present disclosure, an image in which the through-channels are colored is also referred to as a "colored image." One method for obtaining a colored image is to first identify the through-flow paths using the thinned image as described above, then roughly estimate the porosity from the electrode density, and then adjust the contrast using computer processing so that the colored area corresponds to the porosity. By this operation, the porosity on the three-dimensional image is corrected to match the porosity of the electrode active material. For example, if the density of the active material layer is 1.65 g / cm 3 The density of graphite as an active material is 2.2 g / cm 3 In this case, the porosity is (1-1.65 / 2.2) x 100 = 25%. Therefore, in this case, computer processing is performed to color the active material layer so that 25% is void. Note that the active material layer contains a binder and, if necessary, additives, but since the contents of these are small, the porosity can be calculated without taking these contents into consideration.

[0049] The number of colored through-flow paths per unit area on one side of the active material layer (the side on which the electrolyte solution penetrates) is counted.

[0050] The measurement region does not have to be the entire thickness of the active material layer, but may be a part of the thickness direction. In particular, a large number of through-flow paths per unit area on one surface (the surface on the electrolyte inlet side) of the active material layer may mean that there are a large number of openings on one surface of the active material layer, or that the paths branch along their paths, or both, and the paths penetrate to the other surface. Therefore, it is thought that the number of through-flow paths in a region from one surface (the surface on the electrolyte inlet side) of the active material layer to a specific depth (e.g., 50 μm) is more closely correlated with internal resistance. From the above, the image data used to count the number of through-flow paths may be image data of a region from one surface (the surface on the electrolyte inlet side) of the active material layer to a specific depth (for example, 50 μm). In the present disclosure, the flow paths penetrating the region up to such a specific depth are also referred to as through-flow paths.

[0051] The electrode evaluation method of the present disclosure may further include a step of calculating the tortuosity expressed by the following formula (1). T=f / s (1) (In formula (1), T is the tortuosity, f is the total length of the through-flow passage, and s is the distance of a straight line from the opening of the through-flow passage on one surface of the active material layer to the opening of the through-flow passage on the other surface.)

[0052] FIG. 4 is a diagram showing an example of one flow path (central axis) in a thinned view of a cross section in the thickness direction (x-axis direction) of the active material layer (i.e., a cross section from one surface a to the other surface b of the active material layer). The total length of the path indicated by the solid line in Figure 4 corresponds to f in the above formula (1). Also, the distance of the straight line connecting the point where the path intersects on one surface a to the point where the path intersects on the other surface b corresponds to s in the above formula (1).

[0053] FIG. 5 is a diagram showing another example of a flow path (central axis) in a thinned view of a cross section from one surface a to the other surface b of an active material layer. There are cases where the flow path branches along the way, such as the path with one end at the opening C in Figure 5. The following two examples are given as methods for determining the tortuosity of such a flow path.

[0054] First, the first method is to calculate the curvature ratio for all paths. In other words, in the case of Figure 5, this is a method to calculate the curvature ratio for all paths A-A1, B-B1, C-C1, C-C2, and C-C3. For example, the path "A-A1" means the path connecting opening A and opening A1. For example, as shown in FIG. 6(A), a path is explained between surfaces m and n, branching from an opening m1 to three points, openings n1, n2, and n3. For the m1-n1 route, the tortuosity is calculated by setting the total length of the route connecting the openings m1 and n1 to f and the straight-line distance connecting the openings m1 and n1 to s. Similarly, for the route m1-n2, the tortuosity is calculated by setting the total length of the route connecting the openings m1 and n2 as f and the straight-line distance connecting the openings m1 and n2 as s. For the route m1-n3, the tortuosity is calculated by setting the total length of the route connecting the opening m1 and the opening n3 as f and the straight-line distance connecting the opening m1 and the opening n3 as s.

[0055] The second method is to calculate the tortuosity ratio for the shortest paths. In other words, if the path C-C2 is the shortest of the three paths that end at opening C in Figure 5, the tortuosity ratios for the paths A-A1, B-B1, and C-C2 are calculated. In the second method, as shown in Figure 6(B), the smallest curvature ratio among the curvature ratios of the paths m1-n1, m1-n2, and m1-n3 is used as the curvature ratio of the path having the opening m1 at one end (here, the curvature ratio of the path m1-n3). The curvature ratio calculated by the second method is also called the "shortest curvature ratio." Calculating the minimum tortuosity ratio along with the tortuosity ratio allows for a better understanding of the diffusion state of the electrolyte, which is useful for estimating the internal resistance of the electrode.

[0056] The tortuosity ratio indicates a value of 1 or more. A tortuosity ratio of 1 means that the path is straight, and the closer the tortuosity ratio is to 1, the closer the path is to a straight line. The larger the tortuosity ratio, the more twisted the path. In other words, the tortuosity ratio indicates how twisted the path of ions is at the electrode.

[0057] Furthermore, the electrode evaluation method of the present disclosure may include a step of calculating the ratio (penetration rate) of the number of through-flow paths to the number of all open pores on one surface (electrolyte infiltration side) of the active material layer. The penetration rate provides a better understanding of the diffusion state of the electrolyte and is useful for estimating the internal resistance of the electrode. The total number of open pores on one surface of the active material layer can be determined from the thinned image or colored image.

[0058] The evaluation of the relationship between the number of through-flow paths and the battery characteristics, and further the relationship between the tortuosity and the battery characteristics, may be performed with reference to a thinned image or a colored image. The thinned image and the colored image show the distribution of pores. Therefore, for example, by acquiring a thinned image or a colored image of an electrode and measuring the capacity retention rate, etc., and evaluating the relationship between the thinned image or the colored image and the capacity retention rate, etc., it is possible to determine the degree of battery characteristics that are exhibited for a given pore structure. Therefore, it is possible to consider how the pores are distributed to improve the battery characteristics. In other words, with the above configuration, it is possible to obtain information for determining the distribution of pores that is suitable for improving the battery characteristics, based on the relationship between the thinned image or the colored image and the battery characteristics.

[0059] <Method of manufacturing non-aqueous secondary battery electrodes> The method for producing a nonaqueous secondary battery electrode according to the present disclosure includes: a step of visualizing pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detecting the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; predicting the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; determining a composition of the active material layer such that the predicted number of through-flow paths per unit area is equal to or greater than a predetermined value; forming an active material layer having the determined composition on a current collector; Includes.

[0060] In the electrode manufacturing method of the present disclosure, the number of through-flow paths is detected using the electrode evaluation method of the present disclosure described above. Then, the composition of the active material layer, which is the object for which the number of through-flow paths has been detected, is input separately, and the number of through-flow paths per unit area in an active material layer of a hypothetical composition is predicted based on the number of through-flow paths and composition in that active material layer. For example, by determining how the number of through-flow paths per unit area changes when only the type of binder in the active material layer is changed and other compositions are fixed, the number of through-flow paths can be predicted based on the characteristics of the binder species (e.g., the type and number of functional groups).

[0061] 7 and 8 are colored images of one surface of the active material layer when the binder type is changed. FIG. 7 is a colored image of Example 1, which used the binder polymer (A1) obtained in Synthesis Example 1 of the Examples, and FIG. 8 is a colored image of Example 4, which used the binder polymer (A2) obtained in Synthesis Example 2 of the Examples. Comparing FIG. 7 and FIG. 8, it can be seen that the active material layer using the binder polymer (A1) has a larger number of through-flow channels per unit area. In other words, it is presumed that the active material layer using the binder polymer (A1) allows the electrolyte to more easily penetrate the entire active material layer, has superior ion diffusibility, and lowers the internal resistance of the electrode.

[0062] After selecting a suitable binder type, the number of through-flow channels may be detected for active material layers in which the content of each component is varied for that binder type, and the number of through-flow channels may be predicted for an active material layer having a hypothetical content composition.

[0063] By performing such an operation, a composition of the active material layer that will produce a predicted number of through-flow paths per unit area equal to or greater than a predetermined value is determined, and the active material layer having the determined composition is then formed on a current collector to produce an electrode.

[0064] According to the electrode manufacturing method of the present disclosure, an electrode with low internal resistance can be manufactured.

[0065] <Non-aqueous secondary battery> The nonaqueous secondary battery of the present disclosure comprises a nonaqueous secondary battery electrode obtained by the above-described electrode manufacturing method and an electrolyte solution. The nonaqueous secondary battery electrode obtained by the above-described electrode manufacturing method may be a positive electrode, a negative electrode, or both. As long as at least one electrode is a nonaqueous secondary battery electrode obtained by the above-described electrode manufacturing method, the other electrode does not have to be a nonaqueous secondary battery electrode obtained by the above-described electrode manufacturing method. The nonaqueous secondary battery electrode obtained by the above-described electrode manufacturing method is preferably a negative electrode. The nonaqueous secondary battery of the present disclosure uses the above-described electrode for one or both of the positive electrode and the negative electrode, and therefore tends to have low internal resistance of the electrode and high capacity retention rate.

[0066] As a preferred example of the nonaqueous secondary battery of the present disclosure, a lithium ion secondary battery will be described below, but the configuration of the battery is not limited to that described here. The nonaqueous secondary battery of the present disclosure has a positive electrode, a negative electrode, an electrolyte, and, as necessary, components such as a separator housed in an exterior body, and uses the above-described electrode for one or both of the positive electrode and the negative electrode.

[0067] As the electrolyte, it is preferable to use a non-aqueous liquid having ion conductivity. Examples of the electrolyte include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc., and a solution in which an electrolyte is dissolved in an organic solvent is preferable. This is because, when a solution in which an electrolyte is dissolved in an organic solvent is used as the electrolyte, a non-aqueous battery having low internal resistance can be obtained at low manufacturing costs.

[0068] The electrolyte may be an alkali metal salt, and may be selected appropriately depending on the type of active material. Examples of the electrolyte include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, aliphatic lithium carboxylates, etc. Other alkali metal salts can also be used as the electrolyte.

[0069] The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The organic solvent may be used alone or in combination of two or more. Among these, carbonate ester compounds are preferred as the organic solvent, and linear carbonate ester compounds are more preferred. The linear carbonate ester compounds may be used alone or in combination of two or more. Examples of linear carbonate ester compounds include diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC).

[0070] The outer casing may be, but is not limited to, a laminate of aluminum foil and a resin film. The shape of the battery is not particularly limited, and examples thereof include coin, button, sheet, cylindrical, rectangular, and flat types.

[0071] <Selection support device for electrode materials for non-aqueous secondary batteries> The selection support device for a non-aqueous secondary battery electrode material according to the present disclosure includes: a detection unit that visualizes pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; a prediction unit that predicts the number of through-flow paths per unit area in a virtual active material layer composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; a composition determination unit that determines a composition of the active material layer that will result in a predicted number of through-flow paths per unit area of ​​equal to or greater than a predetermined value; Includes.

[0072] Fig. 9 is a block diagram showing an example of the functional configuration of the material selection assisting device 100. As shown in Fig. 9, the material selection assisting device 100 includes a detecting unit 10, a predicting unit 20, and a composition determining unit 30 as its functional configuration.

[0073] The detection unit 10 visualizes pores in a three-dimensional image of a nonaqueous secondary battery electrode having active material layers with varying compositions on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other in each active material layer. The detection of the number of through-flow paths can be performed using the method for counting the number of through-flow paths described in the electrode evaluation method of the present disclosure. The detection unit 10 causes a computer to count the number of through-flow paths.

[0074] The detection unit 10 may include an image input unit 12 that inputs a three-dimensional image of a nonaqueous secondary battery electrode having an active material layer made by changing the composition on a current collector, a visualization unit 14 that visualizes the through-flow paths by thinning or coloring the input three-dimensional image, and a counting unit 16 that counts the number of visualized through-flow paths.

[0075] The prediction unit 20 predicts the number of through-flow paths per unit area in the composition of a hypothetical active material layer based on the input active material layer composition and the detected number of through-flow paths per unit area. The prediction of the number of through-flow paths in the composition of an active material layer with a hypothetical composition can be made by referring to the method described above in the electrode manufacturing method of the present disclosure.

[0076] The prediction unit 20 may include a composition input unit 22 that inputs the composition of the active material layer for which the number of through-flow paths has been counted, a correspondence relationship construction unit 24 that associates the input active material layer composition with the number of through-flow paths detected in that active material layer, a virtual composition input unit 26 that inputs the composition of a virtual active material layer, and a through-flow path number prediction unit 28 that predicts the number of through-flow paths in the virtual active material layer based on the correspondence relationship.

[0077] The composition determination unit 30 determines the composition of the active material layer so that the predicted number of through-flow paths per unit area is equal to or greater than a predetermined value. The composition of the active material layer can be determined by referring to the method described above in the electrode manufacturing method of the present disclosure. The composition determination unit 30 may have the through-flow path number prediction unit 28 predict the number of through-flow paths for multiple virtual active material layers, and determine the composition of an active material layer from the multiple virtual active material layers such that the number of through-flow paths is equal to or greater than a predetermined value.

[0078] The material selection assistance device of the present disclosure can assist in the selection of an electrode composition for manufacturing an electrode with low internal resistance.

[0079] <Program> The program of the present disclosure includes: a detection unit that visualizes pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; a prediction unit that predicts the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; and a composition determination unit that determines a composition of the active material layer that will result in a predicted number of through-flow paths per unit area of ​​at least a predetermined value; This is a program that functions as a

[0080] The detection unit, prediction unit, and composition determination unit in the program of the present disclosure can refer to the detection unit, prediction unit, and composition determination unit in the selection support device of the present disclosure. The computer is configured to include a CPU that controls the entire material selection assisting apparatus 100, a ROM as a storage medium that stores routine programs for the detection unit 10, prediction unit 20, and composition determination unit 30, a RAM that temporarily stores data as a work area, and a bus that connects these. In such a configuration, a program for realizing the function of each component is stored in the ROM, and each function is realized by the CPU executing the program.

[0081] Note that each unit of the selection support device of the present disclosure is not limited to being realized by a computer, but may be configured with multiple computers that realize the functions of each unit, or one or more electronic circuits.

[0082] Furthermore, the present disclosure is not limited to a case where the program is pre-installed in the ROM of a computer, but the program can also be provided by being stored in a storage medium such as a CD-ROM. [Example]

[0083] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the examples described below. In the following examples, a negative electrode of a lithium ion battery is prepared as an example of an electrode. Note that the water used in the following examples and comparative examples is ion-exchanged water unless otherwise specified.

[0084] 1-1. Synthesis Example 1 A monomer emulsion was prepared by mixing and emulsifying the type and amount of monomer (a) shown in Synthesis Example 1 in Table 1 with 200 parts by mass of water. Aqualon KH10, used as the polymerizable surfactant (a6), is polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and is a compound represented by the above formula (2).

[0085] Next, the type and amount of polymerization initiator shown in Synthesis Example 1 in Table 1 was dissolved in 50 parts by mass of water to prepare an aqueous polymerization initiator solution.

[0086] A separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel was charged with 150 parts by mass of water and heated to 75°C. The monomer emulsion and the aqueous polymerization initiator solution were continuously fed into the separable flask over a period of 3 hours while stirring at 75°C, respectively, to carry out emulsion polymerization and obtain an emulsion. The resulting emulsion was cooled to room temperature (25°C). To the cooled emulsion, 17 parts by mass of 25% aqueous ammonia (basic substance in Table 1: 4.25 parts by mass of ammonia, 12.75 parts by mass of water) and 130 parts by mass of water were added. The Rongalit SFS used as the polymerization initiator was manufactured by Sumitomo Seika Chemicals Co., Ltd.

[0087] Through this process, the binder composition of Synthesis Example 1 was obtained as an emulsion containing the binder (A1).

[0088] [1-2. Synthesis Example 2] Monomer (a) of the type and amount shown in Synthesis Example 2 in Table 1 was mixed with 200 parts by mass of water and emulsified to prepare a monomer emulsion.

[0089] Next, the type and amount of radical polymerization initiator shown in Synthesis Example 2 in Table 1 was dissolved in 50 parts by mass of water to prepare an aqueous polymerization initiator solution.

[0090] 200 parts by mass of water was placed in a 5 MPa pressure vessel equipped with a stirrer, and the temperature was raised to 60°C at an internal pressure of 1.0 MPa. The monomer emulsion and the aqueous solution containing the radical polymerization initiator were each added all at once to this pressure vessel, and the mixture was stirred at 60°C for 8 hours to carry out emulsion polymerization, thereby obtaining an emulsion. The obtained emulsion was cooled to room temperature (25°C). To the cooled emulsion, 5.3 parts by mass of 25% ammonia water (basic substance in Table 1: ammonia 1.325 parts by mass, water 3.975 parts by mass) and 130 parts by mass of water were added.

[0091] Through this step, an emulsion containing dispersed particles containing the binder of Synthesis Example 2 and an aqueous medium was obtained as an emulsion containing binder (A2).

[0092] [1-3. Measurement of non-volatile content] 1 g of each of the emulsions obtained in Synthesis Examples 1 and 2 was weighed onto a 5 cm diameter aluminum dish and dried at 105°C for 1 hour with air circulating in a dryer at 1 atmosphere (1013 hPa). The mass of the remaining components was measured to determine the nonvolatile content (mass%). The measured values ​​of the nonvolatile content of the emulsions obtained in Synthesis Examples 1 and 2 are shown in Table 1.

[0093] [1-4. Measurement of glass transition temperature] The emulsions obtained in Synthesis Examples 1 and 2 were each dried at 105°C for 1 hour under circulating air in a dryer at 1 atmosphere (1013 hPa). The remaining components were removed and placed in a sample pan for DSC measurement. The DSC measurement was performed using an EXSTAR DSC / SS7020 (Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min under a nitrogen gas atmosphere. For each Synthesis Example, the peak-top temperature of the DSC chart obtained as the temperature derivative of the DSC was taken as the glass transition temperature (°C) of the binder polymer (A1) or binder polymer (A2). The measured glass transition temperatures of the binder polymer (A1) and binder polymer (A2) are shown in Table 1.

[0094] [Table 1]

[0095] <2. Negative electrode slurry> 2-1. Preparation of negative electrode slurry In each example, the binder, water-soluble polymer, and negative electrode active material shown in Table 2 were used and mixed with water as a liquid medium in the amounts shown in Table 2 to prepare a negative electrode slurry. Specifically, the cellulose derivative, the electrode active material (negative electrode active material), and water were mixed and diluted stepwise to achieve nonvolatile content concentrations of 69%, 67%, 65%, 63%, 61%, and 56% by mass. The resulting 56% by mass negative electrode slurry was then mixed with a binder and water to obtain a 55% by mass negative electrode slurry. The amount of water added at each stage of this process was adjusted so that the total amount, including the water contained in the emulsion, achieved the respective amounts listed above. The nonvolatile content of the negative electrode slurry was measured in accordance with the method for measuring the nonvolatile content of the emulsions in Synthesis Examples 1 and 2 described above.

[0096] As the binder, the binder (A1) synthesized in Synthesis Example 1 or the binder (A2) synthesized in Synthesis Example 2 was used.

[0097] The water-soluble polymer used was sodium carboxymethylcellulose (CMC-Na) with a degree of etherification of 0.70 and a weight-average molecular weight of 2,000,000.

[0098] The following graphite was used as the negative electrode active material. Artificial graphite A: particle size (D50) 14.4 μm, BET specific surface area by nitrogen gas adsorption 1.7 m 2 / g, true density 2.2g / cm 3 Artificial graphite B: particle size (D50) 12.6 μm, BET specific surface area by nitrogen gas adsorption 2.5 m 2 / g, true density 2.2g / cm 3 Natural graphite: particle size (D50) 10.7 μm, BET specific surface area by nitrogen gas adsorption 4.1 m 2 / g, true density 2.2g / cm 3

[0099] [2-2. Non-volatile content of negative electrode slurry] For each of the negative electrode slurries obtained in each Example and Comparative Example, 1 g of the mixture was weighed into a 5 cm diameter aluminum dish and dried at 130°C for 1 hour under circulating air in a dryer at 1 atmosphere (1013 hPa). The mass of the remaining components was measured and the nonvolatile content (mass%) was calculated. The nonvolatile content of the electrode slurries prepared in each Example and Comparative Example is shown in Table 2.

[0100] <3. Negative electrode> [3-1. Preparation of negative electrode] The negative electrode slurry was applied to both sides of a 10 μm thick copper foil (negative electrode current collector) by a direct roll method. The amount of the negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness before the roll press treatment described below would be 130 μm per side.

[0101] The negative electrode slurry coated on the negative electrode current collector was dried by conveying it at 0.4 m / min through a 1.6 m long drying furnace set at 90° C. to obtain a negative electrode sheet.

[0102] [3-2. Evaluation of flow paths in the negative electrode active material layer] The morphology of the flow paths in the negative electrode active material layer was evaluated as follows. The pressed negative electrode sheet was cut into a size of 1 mm × 30 mm to prepare a test piece. A three-dimensional image of the negative electrode active material layer in the test piece was obtained using a microfocus X-ray CT system SMX-160CTS manufactured by Shimadzu Corporation under the following conditions.

[0103] Incident X-ray tube voltage: 50 kV Measurement procedure: The longitudinal direction of the test piece is the z-direction, and the test piece is rotated around a rotation axis parallel to the z-direction, while X-rays are irradiated toward the test piece mainly in a direction perpendicular to the z-direction. Resolution: 360° divided into 1200 sections (0.3° intervals)

[0104] The porosity of the negative electrode active material layer was calculated from the density of the negative electrode active material layer and the density of the artificial graphite. The obtained porosity is shown in Table 2. Based on this porosity, the pores (flow paths) in the three-dimensional image were colored by computer processing, and a colored image was obtained.

[0105] Then, the number of through-flow channels per unit area was measured within the following measurement range using three-dimensional image analysis software (ExFact VR and ExFact Analysis for Porous Particles, manufactured by Nippon Visual Science Co., Ltd.).

[0106] The longitudinal direction of the test piece was the z-direction, the lateral direction was the y-direction, and the thickness direction was the x-direction. The measurement range in the yz plane was 200 μm × 200 μm, and the center of the measurement range was aligned with the center of the electrode active material layer. The measurement range in the x-direction was extended to a depth of 50 μm from the surface of the electrode active material layer.

[0107] Furthermore, using three-dimensional image analysis software (ExFact VR and ExFact Analysis for Porous Particles, manufactured by Nippon Visual Science Co., Ltd.), the total length of the through-flow passage and the distance drawn by a straight line from the opening on one side of the through-flow passage to the opening on the other side of the through-flow passage were measured, and the tortuosity was calculated using the above formula (1). The tortuosity of all the through-flow passages in the above measurement range was analyzed, and the average of the obtained tortuosity values ​​is shown in Table 2.

[0108] Figure 1 shows X-ray CT images of the outer surfaces of the negative electrode active material layers of Examples 1 and 4. The X-ray CT images in Figure 1 are colored images in which pores (through-flow paths) extending from the surface to a depth of 50 µm are colored. 2 also shows SEM photographs of the surfaces of the negative electrode active material layers of Examples 1 and 4. However, the SEM photographs in FIG. 2 were taken at a different location than the X-ray CT image in FIG.

[0109] [3-3. Measurement of electrode density] The 10 μm thick copper foil used as the negative electrode current collector was cut into a 52 mm × 42 mm (= 5.2 cm × 4.2 cm) piece, and the mass m0 [mg] of the copper foil piece was measured. In each example and comparative example, the mass m1 [mg] of the negative electrode (52 mm × 42 mm = 5.2 cm × 4.2 cm) before the conductive tab was attached was also measured. The difference between the mass m1 of the negative electrode and the mass m0 of the copper foil piece is divided by the area of ​​the copper foil piece and the negative electrode to obtain the mass M [mg / cm 2 ] was calculated. 2 ](=1 / 1000×M[g / cm 2 ]) by the thickness of the electrode active material layer (130 μm (=0.0130 cm) in this example and comparative example), the electrode density [g / cm 3 ] was calculated. The true density of artificial graphite A, artificial graphite B, and natural graphite A used as electrode active materials was 2.2 g / cm. 3 The filling rate of the electrode active material in the electrode active material layer was calculated as follows.

[0110] <4. Lithium-ion secondary battery> 4-1. Battery Construction A lithium ion secondary battery was fabricated using the negative electrode according to each example. In the following description, the fabrication of the negative electrode was as described above, and the obtained negative electrode sheet was cut into a size of 52 mm x 42 mm, and a conductive tab was attached to fabricate the negative electrode.

[0111] LiNi as the positive electrode active material 0.6 Mn 0.2 Co 0.2 A positive electrode slurry was prepared by mixing 94 parts by mass of O2, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder, to which 50 parts by mass of N-methylpyrrolidone was added and further mixed.

[0112] The positive electrode slurry was applied to both sides of a 15 μm thick aluminum foil (positive electrode current collector) by a direct roll method. The amount of the positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described below would be 125 μm per side.

[0113] The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes and pressed with a roll press (manufactured by Thank Metals, press load 5 t, roll width 7 cm) to obtain a positive electrode sheet with a positive electrode active material layer formed on the current collector. The obtained positive electrode sheet was cut into a size of 50 mm x 40 mm, and a conductive tab was attached to prepare a positive electrode.

[0114] A separator (25 μm thick) made of a polyolefin-based porous film was placed between the positive and negative electrodes, and the positive and negative active material layers were placed facing each other in an aluminum laminate exterior (battery pack). The exterior was filled with an electrolyte solution, vacuum-impregnated, and sealed with a vacuum heat sealer to prepare a lithium-ion secondary battery for evaluation. The electrolyte solution was prepared by mixing 99 parts by weight of a 1.0 mol / L solution of LiPF6 in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 30 / 50 / 20, with 1 part by weight of vinylene carbonate.

[0115] [4-2. Measuring internal resistance] The internal resistance (DCR (Ω)) of the lithium ion secondary battery was measured at 25° C. by the following procedure. First, the state of charge was set to 50% of the initial capacity (SOC50%) at 0.2 C. Then, the battery was discharged for 60 seconds at current values ​​of 0.2 C, 0.5 C, 1 C, and 2 C. The internal resistance DCR (Ω) at SOC50% was determined from the relationship between these four current values ​​(values ​​over 1 second) and voltage.

[0116] [Table 2]

[0117] <5. Evaluation Results> It can be seen that the number of through-flow paths analyzed based on the electrode evaluation method of the present disclosure correlates with the internal resistance of the electrode. [Explanation of symbols]

[0118] 3 center axis 4 Stenosis 5a, 5b, 5c, 5d Space within the pores 10. Detection unit 12 Image input unit 14 Visualization part 16 Counting section 20 Prediction Department 22 Composition input section 24 Correspondence Building Department 26 Virtual composition input section 28 Number of through-flow paths prediction section 30 Composition Determination Department 100 Material selection support device

Claims

1. obtaining a three-dimensional image of a non-aqueous secondary battery electrode having an active material layer including an active material and a binder on a current collector; a step of visualizing pores in the active material layer in the three-dimensional image and analyzing the number of through-flow paths per unit area that penetrate from one surface to the other surface of the active material layer; A method for evaluating a non-aqueous secondary battery electrode, comprising:

2. The method for evaluating a nonaqueous secondary battery electrode according to claim 1 , further comprising the step of calculating a tortuosity of the through-flow path represented by the following formula (1): T = f / s (1) (In formula (1), T is the tortuosity, f is the total length of the through-flow path, and s is the distance of a straight line from the opening of the through-flow path on one surface of the active material layer to the opening of the through-flow path on the other surface.)

3. a step of visualizing pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detecting the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; predicting the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; determining a composition of the active material layer such that the predicted number of through-flow paths per unit area is equal to or greater than a predetermined value; forming an active material layer having the determined composition on a current collector; A method for producing a non-aqueous secondary battery electrode, comprising:

4. a detection unit that visualizes pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; a prediction unit that predicts the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; a composition determination unit that determines a composition of the active material layer that will result in a predicted number of through-flow paths per unit area of ​​equal to or greater than a predetermined value; A selection support device for electrode materials for non-aqueous secondary batteries, comprising:

5. Computer, a detection unit that visualizes pores in a three-dimensional image of a plurality of nonaqueous secondary battery electrodes having active material layers with different compositions formed on a current collector, and detects the number of through-flow paths per unit area that penetrate from one surface to the other surface of each active material layer; a prediction unit that predicts the number of through-flow paths per unit area in an active material layer having a hypothetical composition based on the input composition of the active material layer and the detected number of through-flow paths per unit area; and a composition determination unit that determines a composition of the active material layer that will result in a predicted number of through-flow paths per unit area of ​​at least a predetermined value; A program to function as a

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