Electrode active material layer, nonaqueous secondary battery electrode, and nonaqueous secondary battery

Abstract

Provided is an electrode active material layer which contains an electrode active material, wherein: the thickness of the electrode active material layer is 50 µm or more; the number of through passages, which reach a depth of 50 µm from the surface of the electrode active material layer, per unit area is 3.50 passages / µm2 or more as determined by visualizing pores of the electrode active material layer in a three-dimensional image that is obtained by X-ray CT scanning of the electrode active material layer; and the density of the electrode active material layer is 1.20 g / cm3 or more.

Description

Electrode active material layer, non-aqueous secondary battery electrode, and non-aqueous secondary battery

[0001] The present disclosure relates to an electrode active material layer, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery.

[0002] A nonaqueous secondary battery has a configuration including, for example, a positive electrode using a metal oxide or the like as an electrode active material, a negative electrode using a carbon material such as graphite as an electrode 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] 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 electrode active material for electrodes of non-aqueous electrolyte energy devices, and (b) a mixed solvent of a good solvent for the binder resin and a poor solvent for the binder resin, the good solvent having a boiling point lower than that of the poor solvent. Patent Document 1 explains that the binder resin composition uses a mixed solvent consisting of a good solvent that dissolves the polymer and a poor solvent that does not dissolve the polymer as a solvent for dissolving the binder polymer, and therefore the electrode active material is bound without being covered with the binder resin, thereby reducing the internal resistance of the electrode.

[0004] 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 from the perspective of environmentally friendly vehicle applications. For these applications, non-aqueous secondary batteries are required to have high charge / discharge capacities.

[0005] JP 2011-134492 A

[0006] In order to ensure a large charge / discharge capacity, it is necessary to increase the electrode density of the electrode active material layer. However, increasing the electrode density makes it difficult for ions to move within the electrode active material layer, which tends to result in an increase in the internal resistance of the battery. Therefore, in non-aqueous secondary batteries, there is a trade-off between charge / discharge capacity and internal resistance. Therefore, the present disclosure provides an electrode active material layer and a non-aqueous secondary battery electrode that can provide a non-aqueous secondary battery with a large charge / discharge capacity and low internal resistance, as well as a non-aqueous secondary battery using the same.

[0007] The present disclosure includes the following aspects: <1> An electrode active material layer containing an electrode active material, wherein the thickness of the electrode active material layer is 50 μm or more, and the number of through-flow paths per unit area that reach a depth of 50 μm from the surface of the electrode active material layer, detected by processing data obtained by X-ray CT scanning of the electrode active material layer, is 3.50 paths / μm ２ or more, and the density of the electrode active material layer is 1.20 g / cm ３ or more. <2> The electrode active material layer according to <1>, wherein the thickness of the electrode active material layer is 60 μm or more. <3> The electrode active material layer according to <1> or <2>, wherein the electrode active material layer contains 80 mass% or more of the electrode active material. <4> The electrode active material layer according to any one of <1> to <3>, wherein a packing factor, which is the ratio of the electrode density of the electrode active material layer to the true density of the electrode active material, is 50% or more. <5> The electrode active material layer according to any one of <1> to <4>, wherein the electrode active material contains 50 mass% or more of graphite. <6> The electrode active material layer according to any one of <1> to <5>, wherein the tortuosity ratio of the through-flow paths, represented by the following formula (1), is 3.00 or less: 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 in a straight line from the opening of the through-flow path on one surface of the electrode active material layer to the opening of the through-flow path on the other surface.) <7> A non-aqueous secondary battery electrode having a current collector and the electrode active material layer according to any one of <1> to <6>. <8> A non-aqueous secondary battery comprising the electrode according to <7>.

[0008] According to the present disclosure, it is possible to provide an electrode active material layer that allows for the production of a nonaqueous secondary battery with a large charge / discharge capacity and low internal resistance, a nonaqueous secondary battery electrode, and a nonaqueous secondary battery using the same.

[0009] 1A and 1B are X-ray CT images in which pores in the electrode active material layers in Examples 1 and 4 are colored. 1C are scanning electron microscope (SEM) photographs of the surfaces of the electrode active material layers in Examples 1 and 4. 1D are examples of colored images. 1E are examples of colored images when the binder type is changed.

[0010] The following describes the embodiments in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the 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. For example, the present disclosure allows addition, omission, substitution, modification, etc. of the number, amount, position, ratio, material, configuration, type, order, etc., within the scope of the spirit of the present disclosure.

[0011] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, the content or amount of each component refers to 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 layer is observed, as well as cases where the layer is formed only in a portion of the area. In the present disclosure, "(meth)acrylic" is a general term for acrylic and methacrylic. "(meth)acrylate" is a general term for acrylate and methacrylate. In the present disclosure, unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability.

[0012] <Electrode active material layer> The electrode active material layer of the present disclosure is an electrode active material layer containing an electrode active material, the electrode active material layer has a thickness of 50 μm or more, and the number of through-flow paths per unit area that reach a depth of 50 μm from the surface of the electrode active material layer, as detected by processing data obtained by X-ray CT scanning, is 3.50 paths / μm ２ or more, and the density of the electrode active material layer is 1.20 g / cm ３ That's all. The electrode active material layer of the present disclosure may be a positive electrode active material layer or a negative electrode active material layer. Hereinafter, the "number of through-flow paths per unit area that reach a depth of 50 μm from the surface of the electrode active material layer" will also be referred to as the "number of through-flow paths." In the present disclosure, one surface of the electrode active material layer is the outer surface opposite the current collector side, where the electrolyte solution penetrates, and the other surface of the electrode active material layer is the surface on the current collector side.

[0013] The electrode active material layer having the above-described structure provides a non-aqueous secondary battery with a large charge / discharge capacity and low internal resistance. The reason for this is presumed to be as follows: When the density of the electrode active material layer is 1.20 g / cm ３ Since the above conditions are met, a high charge / discharge capacity is maintained. It has also been found that the ease of ion diffusion within the electrode is related to the number of flow paths per unit area of ​​the electrode active material layer. The pores in the electrode active material layer exist not only as through-flow paths that penetrate from one surface of the electrode active material layer to the other, but also as flow paths that terminate midway from one surface of the electrode active material layer, and as independent pores that do not open to the surface of the electrode active material layer. Among these flow paths, it has been found that the number of flow paths that reach a depth of 50 μm from one surface of the electrode active material layer (the surface on the electrolyte inlet side) is effective in reducing internal resistance.

[0014] From the above, in the present disclosure, a flow path that reaches a depth of 50 μm from the surface of the electrode active material layer is referred to as a through flow path, and the number of these through flow paths per unit area is set to 3.50 / μm. ２ It has been found that this reduces the internal resistance of the electrode.

[0015] The thickness of the electrode active material layer is preferably 60 μm or more, more preferably 65 μm or more, and even more preferably 70 μm or more. When the thickness of the electrode active material layer is within the above range, the charge / discharge capacity of the non-aqueous secondary battery tends to be improved. The thickness of the electrode active material layer is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. When the thickness of the electrode active material layer is within the above range, the electrode resistance of the non-aqueous secondary battery tends to be reduced.

[0016] The thickness of the electrode active material layer is measured with a micrometer and is defined as the arithmetic mean value of measurements obtained at five arbitrarily selected points. When the electrode active material layer is provided on both sides of the current collector, the thickness of the electrode active material layer is the thickness per side.

[0017] The electrode active material layer preferably contains 80% by mass or more of the electrode active material, more preferably 90% by mass or more, and even more preferably 93% by mass or more. When the content of the electrode active material in the electrode active material layer is within the above range, the charge / discharge capacity of the nonaqueous secondary battery tends to be improved.

[0018] The content of the electrode active material in the electrode active material layer is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less. When the content of the electrode active material in the electrode active material layer is within the above range, bonding between the electrode active materials and between the electrode active material and the current collector is facilitated, and the content of components for forming a conductive path, such as the water-dispersible polymer and water-soluble polymer described below, is easily ensured. The content of the electrode active material in the electrode active material layer is preferably 80% by mass to 99% by mass, more preferably 90% by mass to 98% by mass, and even more preferably 93% by mass to 97% by mass. Details of examples of materials used as the electrode active material will be described later.

[0019] (Density) The density of the electrode active material layer is 1.20 g / cm ３ or more, and 1.40 g / cm ３ It is preferable that the density is 1.50 g / cm or more. ３ More preferably, it is 1.60 g / cm or more. ３ More preferably, this is because the charge / discharge capacity of the electrode and the battery can be increased.

[0020] The electrode density of the electrode active material layer is the mass (weight) of the electrode active material layer per unit area of ​​the electrode [g / cm ２ ] by the thickness [cm] of the electrode active material layer described below.

[0021] (Number of through-flow channels) The number of through-flow channels in the electrode active material layer is 3.50 / μm. ２ or more, 4.50 lines / μm ２ Preferably, the number of fibers is 5.00 or more. ２ More preferably, it is 5.30 lines / μm or more. ２The reason for setting the number of through-flow paths in the above range is that the internal resistance of the battery can be effectively reduced. ２ Preferably, the number of fibers is 20 or less per μm. ２ More preferably, it is 10 lines / μm or less. ２ It is more preferable that the number of through-flow paths is within the above range in order to prevent cracks from occurring in the electrode. The method for measuring the number of through-flow paths is as follows.

[0022] (1) Preparation of Test Piece An electrode having an electrode active material layer containing an electrode active material on a current collector was prepared, and the electrode was cut into a width of 2 mm to prepare a test piece having a length of more than 2 mm.

[0023] (2) Data Acquisition Measurement data on the electrode active material layer is obtained by X-ray CT scanning using the following equipment and operating conditions.

[0024] X-ray CT device: SMX-160CTS manufactured by Shimadzu Corporation Incident X-ray tube voltage: 50 kV Measurement procedure: The longitudinal direction of the test piece is the z direction, and while the test piece is rotated around a rotation axis parallel to the z direction, X-rays are irradiated toward the test piece centered on a direction perpendicular to the z direction. Resolution: 360° divided into 1200 parts (0.3° intervals)

[0025] (3) Analysis Based on the data obtained from the above measurements, analysis is performed using the following analysis software within the following measurement range. If the same analysis results are obtained, analysis may be performed using other analysis software, but in this disclosure, the value obtained under the following conditions is used as the number of through-flow paths.

[0026] Analysis software: 3D image analysis software (ExFact VR and ExFact Analysis for Porous Particles, manufactured by Nippon Visual Science Co., Ltd.) Analysis range: The longitudinal direction of the test piece is the z direction, the lateral direction is the y direction, and the thickness direction is the x direction, with the measurement range in the yz plane being 200 μm × 200 μm, and the center of the measurement range coinciding with the center of the electrode active material layer. The measurement range in the x direction is from the surface of the electrode active material layer to a depth of 50 μm.

[0027] In the above analysis, data is assigned to each position on the data within the measurement range to determine whether or not that position is a void. The void ratio is used as the data to determine whether or not that position is a void. Here, the void ratio is a value calculated from the packing ratio of the electrode active material by (100 - packing ratio). The packing ratio of the electrode active material is calculated by the true density D of the electrode active material. ０ [g / cm ３ ] the electrode density D of the electrode active material layer Ｅ [g / cm ３ ]Ratio D Ｅ / D ０ (D as a percentage Ｅ / D ０ For example, when the density of the negative electrode active material layer is 1.65 g / cm ３ The density of graphite as an electrode active material is 2.2 g / cm ３ In this case, the porosity is (1-1.65 / 2.2) x 100 = 25%. Note that although the negative electrode active material layer contains a binder and, if necessary, an additive, the contents of these are small, so the porosity is calculated without taking these contents into consideration.

[0028] The data obtained by the above measurement is binarized using analysis software. The boundary conditions for binarization are set so that the measured porosity and the calculated porosity match. Based on the binarized data, the pores are thinned, and based on the thinned data, the number of through-flow channels per unit area reaching a depth of 50 μm from the surface of the electrode active material layer is measured using the above analysis software. In the analysis software, the depth direction of the electrode active material layer is selected as the measurement direction for the number of through-flow channels.

[0029] The filling rate of the electrode active material is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. The filling rate of the electrode active material is set in the above range in order to further increase the charge / discharge capacity of the electrode and the battery. When the electrode active material contains two or more substances, the true density D of the electrode active material is ０ [g / cm ３ ] can be calculated as follows:

[0030] From the viewpoint of reducing internal resistance, the tortuosity of the through-flow path, expressed by the following formula (1), is preferably 3.00 or less, more preferably 2.50 or less, and even more preferably 1.80 or less. Furthermore, the tortuosity is preferably 1.20 or more, more preferably 1.40 or more, and even more preferably 1.60 or more. This is because, when the tortuosity is within the above range, the area in contact with the flow path of the electrolyte increases, thereby improving the electrical conductivity in the electrode active material layer.

[0031] T=f / s (1)

[0032] In formula (1), T is the tortuosity, f is the total length of the through-flow path, and s is the distance drawn in a straight line from the opening of the through-flow path on one side of the electrode active material layer to the opening of the through-flow path on the other side.

[0033] The tortuosity ratio in the present disclosure is an average value of the tortuosity ratios obtained by analyzing the tortuosity ratios of all through-flow paths in the analysis range using the above-mentioned analysis software. The preferred range of the tortuosity ratio is when the depth direction of the electrode active material layer is selected as the measurement direction in the above-mentioned analysis software.

[0034] (Composition) The electrode active material layer of the present disclosure contains an electrode active material and a binder, and has a number of through-flow paths of 3.50 / μm. ２ or more, and the density is 1.20 g / cm ３ As long as the composition is as described above, there are no particular limitations on the composition, and any composition used in the relevant field can be applied as appropriate.

[0035] (1) Binder As the binder, it is preferable to use a polymer using, as a monomer, an ethylenically unsaturated compound having a group that becomes a side chain when polymerized. For example, polyolefins such as butadiene do not have a group that becomes a side chain when polymerized, while styrene, (meth)acrylic acid ester, etc. have a group that becomes a side chain when polymerized. When a polymer having a side chain is used, many through-flow channels tend to be formed even when the electrode active material layer is pressed to increase the density of the electrode active material layer.

[0036] Preferred examples of the binder include, but are not limited to, copolymers of aromatic ethylenically unsaturated compounds, nonionic (meth)acrylic acid esters, and anionic unsaturated compounds. The binder may have a crosslinked structure. The particles formed by the binder may contain a surfactant or the like.

[0037] 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.

[0038] The nonionic (meth)acrylic acid ester is preferably a nonionic aliphatic compound having one (meth)acryloyl group. Examples of (meth)acrylic acid alkyl esters 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.

[0039] 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.

[0040] From the viewpoint of polymerization stability of the binder, the binder is an ammonium salt of a sulfo group (-SO３ NH ４ ) is preferably present.

[0041] 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.

[0042] 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.

[0043] The glass transition point Tg of the binder is preferably −30° C. or higher, more preferably −20° C. or higher, and even more preferably −10° C. or higher. This is because, when the glass transition point Tg of the binder is within the above range, the cycle characteristics of a nonaqueous secondary battery including a nonaqueous secondary battery electrode of the present disclosure are improved. The glass transition point Tg of the binder is preferably 100° C. or lower, more preferably 50° C. or lower, and even more preferably 30° C. or lower. This is because, when the glass transition point Tg of the binder is within the above range, the adhesion of the negative electrode active material layer containing the binder to the current collector foil is improved.

[0044] (2) Electrode Active Material The electrode 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.

[0045] When the electrode is a negative electrode, the electrode active material, i.e., the negative electrode active material, preferably contains at least one selected from the group consisting of a carbon material, a silicon-containing material, and a titanium-containing material. Examples of carbon materials used as the electrode 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.

[0046] The negative electrode active material more preferably contains at least one selected from the group consisting of a carbon material and a silicon-containing material, further preferably contains a carbon material, particularly preferably contains graphite, and extremely preferably contains artificial graphite, because the effects of the present disclosure are particularly large when the negative electrode active material contains these materials.

[0047] When the electrode is a positive electrode, the electrode active material, i.e., the positive electrode active material, is a material having a more noble standard electrode potential than the negative electrode active material. Examples of the positive electrode active material include lithium composite oxides containing nickel, 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 ２ ) ; Spinel-type lithium manganese oxide (LiMn ２ O ４ ); olivine-type lithium iron phosphate; TiS ２ Chalcogen compounds such as MnO ２ , MoO ３ , V ２ O ５ As the positive electrode active material, one of these substances may be used alone, or two or more of them may be used in combination.

[0048] From the viewpoint of particularly maximizing the effects of the present disclosure, the electrode active material preferably contains 50 mass % or more of graphite, more preferably 70 mass % or more, and even more preferably 90 mass % or more. The electrode active material may contain 100 mass % of graphite.

[0049] Examples of graphite that may be included as the electrode active material include, but are not limited to, artificial graphite, natural graphite, and a mixture of artificial graphite and natural graphite. Examples of graphite forms include, but are not limited to, flake graphite and lump graphite. The electrode active material may also include multiple forms of graphite.

[0050] (3) Water-Dispersible Polymer and Water-Soluble Polymer The negative electrode active material layer preferably contains at least one selected from the group consisting of water-dispersible polymers and water-soluble polymers, and more preferably contains a water-dispersible polymer and a water-soluble polymer.

[0051] The water-dispersible polymer has a solubility in water of 0.50 g / 100 gH ２ The water-dispersible polymer is a polymer compound having a molecular weight of 0 or less. The water-dispersible polymer may have a crosslinked structure. The particles formed by the water-dispersible polymer may contain a surfactant or the like. Preferred examples of the water-dispersible polymer include, but are not limited to, copolymers with aromatic ethylenically unsaturated compounds, nonionic (meth)acrylic acid esters, and anionic unsaturated compounds.

[0052] 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.

[0053] The nonionic (meth)acrylic acid ester is preferably a nonionic aliphatic compound having one (meth)acryloyl group. Examples of (meth)acrylic acid alkyl esters 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.

[0054] 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.

[0055] When the water-dispersible polymer 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.

[0056] The water-dispersible polymer may be a polymer polymerized using a polymerizable surfactant, which is a compound that has an ethylenically unsaturated bond and functions as a surfactant.

[0057] The glass transition temperature Tg of the water-dispersible polymer is preferably −30° C. or higher, more preferably −20° C. or higher, and even more preferably −10° C. or higher. Setting the glass transition temperature Tg of the water-dispersible polymer within the above range improves the cycle characteristics of a nonaqueous secondary battery including a nonaqueous secondary battery electrode of the present disclosure. The glass transition temperature Tg of the water-dispersible polymer is preferably 100° C. or lower, more preferably 50° C. or lower, even more preferably 30° C. or lower, and particularly preferably 10° C. or lower. Setting the glass transition temperature Tg of the water-dispersible polymer within the above range improves the adhesion of an electrode active material layer containing the water-dispersible polymer to a current collecting foil.

[0058] When the electrode active material layer contains a water-dispersible polymer, the content of the water-dispersible polymer in the electrode active material layer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. When the content of the water-dispersible polymer in the electrode active material layer is within the above range, the binding strength between the electrode active materials and between the electrode active material and the current collector tends to be improved. When the electrode active material layer contains a water-dispersible polymer, the content of the water-dispersible polymer in the electrode active material layer is preferably 10% by mass or less, more preferably 5.0% by mass or less, and even more preferably 3.0% by mass or less. When the content of the water-dispersible polymer in the electrode active material layer is within the above range, the content of the electrode active material in the electrode active material is easily increased.

[0059] The solubility of water-soluble polymers is 10g / 100gH ２ The water-soluble polymer is a polymer having a water-soluble group of 0 or more. Preferred examples of the water-soluble polymer include, but are not limited to, cellulose derivatives. The cellulose derivative has a structure in which at least a portion of the hydrogen atoms of hydroxyl groups contained in cellulose are substituted. The cellulose derivative is thought to significantly contribute to the formation of conductive paths between electrode active materials and between the electrode active material and the current collector in the electrode active material layer. Furthermore, adding a cellulose derivative to an electrode slurry containing an electrode active material in the electrode manufacturing process tends to facilitate dispersion of the electrode active material, thereby reducing the manufacturing cost of the electrode.

[0060] Examples of cellulose derivatives include carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, and salts of CMC. One type of cellulose derivative may be used alone, or two or more types may be used in combination. The cellulose derivative preferably contains at least one selected from the group consisting of CMC and salts of CMC, and more preferably contains a salt of CMC. Examples of salts of CMC include alkali metal salts of CMC and ammonium salts of CMC, and alkali metal salts of CMC are preferred. The alkali metal in the alkali metal salt is preferably Na, K, or Li, and more preferably Na.

[0061] The weight-average molecular weight of the water-soluble polymer is preferably 800,000 or more, more preferably 1,200,000 or more, and even more preferably 1,600,000 or more. Setting the weight-average molecular weight of the water-soluble polymer within the above range further improves the binding strength between electrode active materials and between the electrode active material and the current collector. Furthermore, setting the weight-average molecular weight of the water-soluble polymer within the above range is thought to contribute to the formation of conductive paths between the electrode active materials and between the electrode active material and the current collector, thereby further reducing electrode resistance.

[0062] The weight-average molecular weight of the water-soluble polymer is preferably 10 million or less, more preferably 5 million or less, and even more preferably 3 million or less. When the weight-average molecular weight of the water-soluble polymer is within the above range, an increase in the viscosity of the liquid tends to be suppressed during the electrode manufacturing process when producing a liquid containing the water-soluble polymer, such as a slurry containing the water-soluble polymer and an electrode active material. This enables sufficient stirring, improving quality and reducing the manufacturing costs required for stirring. Furthermore, improved application of the water-soluble polymer-containing liquid to the electrode reduces manufacturing costs, and electrode quality is improved by making it easier to control the film thickness. The weight-average molecular weight of the water-soluble polymer may be 800,000 to 10 million, 1.2 million to 5 million, or 1.6 million to 3 million.

[0063] The weight-average molecular weight of the water-soluble polymer is a pullulan-equivalent value measured by GPC. Specific measurement conditions are as follows: GPC device: GPC-101 (manufactured by Resonac Co., Ltd.) Solvent: 0.1 M NaNO ３ Aqueous solution Sample column: Shodex Column Ohpak SB-806 HQ (8.0 mm I.D. x 300 mm) x 2 Reference column: Shodex Column Ohpak SB-800 RL (8.0 mm I.D. x 300 mm) x 2 Column temperature: 40°C Sample concentration: 0.1% by mass Detector: RI-71S (Shimadzu Corporation) Flow rate: 1 ml / min Molecular weight standard: Pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (Resonac Corporation))

[0064] When the electrode active material layer contains a water-soluble polymer, the content of the water-soluble polymer in the electrode active material layer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more. When the content of the water-soluble polymer in the electrode active material layer is within the above range, the binding strength between the electrode active materials and between the electrode active material and the current collector tends to be improved. When the electrode active material layer contains a water-soluble polymer, the content of the water-soluble polymer in the electrode active material layer is preferably 10% by mass or less, more preferably 5.0% by mass or less, and even more preferably 3.0% by mass or less. When the content of the water-soluble polymer in the electrode active material layer is within the above range, the content of the electrode active material in the electrode active material tends to be increased.

[0065] Examples of materials that can be used as the water-dispersible polymer and the water-soluble polymer will be described in detail below.

[0066] When the electrode active material layer contains a water-dispersible polymer and a water-soluble polymer, the total content of the water-dispersible polymer and the water-soluble polymer in the electrode active material layer is preferably 1.0 mass% or more, more preferably 2.0 mass% or more, and even more preferably 3.0 mass% or more. When the total content of the water-dispersible polymer and the water-soluble polymer in the electrode active material layer is within the above range, the binding strength between the electrode active materials and between the electrode active material and the current collector tends to be improved.

[0067] When the electrode active material layer contains a water-dispersible polymer and a water-soluble polymer, the total content of the water-dispersible polymer and the water-soluble polymer in the electrode active material layer is preferably 20% by mass or less, more preferably 10.0% by mass or less, and even more preferably 6.0% by mass or less. When the total content of the water-dispersible polymer and the water-soluble polymer in the electrode active material layer is within the above range, the content of the electrode active material in the electrode active material tends to be increased.

[0068] The total content of the electrode active material, water-dispersible polymer, and water-soluble polymer in the electrode active material layer is preferably 81% by mass or more, more preferably 91% by mass or more, and even more preferably 95% by mass or more. When the total content is within the above range, the content of the electrode active material can be increased, and the electrode resistance tends to be reduced.

[0069] (4) Other Components The electrode active material layer may contain other components such as a conductive aid, a surfactant, and other additives.

[0070] <Electrode> The electrode of the present disclosure includes a current collector and an electrode active material layer of the present disclosure. 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 primary component. When the nonaqueous secondary battery electrode is a negative electrode for a lithium-ion secondary battery, the current collector preferably contains copper as a primary component. "Containing metal A as a primary component" includes cases where metal A and inevitable impurities are contained, cases where two or more metals including metal A are used in combination and metal A has the largest mass proportion, and cases where metal A is an alloy of two or more metals including metal A and metal A has the largest mass proportion. The current collector preferably contains 90 mass% or more, and even more preferably 95 mass% or more, of copper. The current collector may be composed of copper and inevitable impurities. The thickness of the current collector is preferably 0.001 mm to 0.5 mm. The current collector may be a metal sheet.

[0071] The electrode of the present disclosure includes the electrode active material layer of the present disclosure, and therefore has a large charge / discharge capacity and low internal resistance.

[0072] <Electrode Manufacturing Method> An electrode can be manufactured, for example, by applying an electrode slurry containing an electrode active material and a dispersion medium to a current collector, drying the slurry to form an electrode active material layer, and then cutting the layer to an appropriate size. The dispersion medium is preferably an aqueous medium. The method for applying the electrode slurry to the current collector is not particularly limited, and examples 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, taking into consideration the physical properties of the electrode slurry, such as viscosity, and drying properties, the doctor blade method, knife method, or extrusion method is preferred. Applying these application methods tends to result in an electrode active material layer with a smooth surface and small thickness variation.

[0073] The electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. When applying the electrode slurry to both sides of the current collector, the electrode slurry may be applied sequentially to each side, or may be applied to both sides at once. 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 15 mg / cm ２ It is preferable that the amount of the electrode paste applied to each surface be less than 1000 ppm (when applied to both surfaces, the amount applied per surface). This is because the occurrence of cracks on the electrode surface can be suppressed during the drying process of the electrode slurry.

[0074] An electrode active material layer is formed on the current collector by drying the electrode slurry applied to the current collector. The method for drying the electrode slurry is not particularly limited, and examples include hot air, reduced pressure or vacuum environment, (far) infrared rays, and low-temperature air, which can be used alone or in combination of two or more. The drying temperature and drying time of the electrode slurry can be appropriately adjusted depending on the nonvolatile content concentration in the electrode slurry, the amount applied to the current collector, and the like. The drying temperature is preferably 40°C to 350°C, and more preferably 60°C to 200°C from the viewpoint of productivity. The drying time is preferably 1 minute to 30 minutes.

[0075] The electrode sheet in which the electrode 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.

[0076] Before or after cutting the electrode sheet, the electrode sheet may be pressed as needed. Pressing allows the electrode active material to be more firmly bonded to the current collector, further thinning the electrode, thereby enabling the miniaturization of the non-aqueous battery. In addition, when the density of the electrode active material layer is 1.20 g / cm ３ The above adjustment may be performed by pressing.

[0077] As the pressing method, a general method can be used, and it is preferable to use a mold pressing method or a roll pressing method. In the case of the mold pressing method, the pressing pressure is not particularly limited, but is preferably 0.1 t / cm ２ ~5t / cm ２ In the case of the roll press method, the linear pressure is not particularly limited, but is preferably 0.1 t / cm to 5 t / cm. When the press pressure or linear pressure is within the above range, the above effects of pressing can be obtained, while a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into and from the electrode active material tends to be suppressed.

[0078] The number of through-flow channels is 3.50 / μm. ２ A method for producing a negative electrode having the above-mentioned electrode active material layer includes a method in which the nonvolatile content of the slurry is gradually reduced in a step of preparing a slurry containing an electrode active material and a water-soluble polymer. For example, the method may include a step of gradually reducing the nonvolatile content of the slurry by adding and mixing a liquid medium to the slurry containing the electrode active material and the water-soluble polymer, and then further adding and mixing the liquid medium, and when the nonvolatile content of the slurry reaches a predetermined concentration, further adding and mixing the water-dispersible polymer and the liquid medium.

[0079] In the above steps of this production example, the initial nonvolatile concentration of the slurry containing the electrode active material and the water-soluble polymer may be, for example, 60% to 90% by mass, 60% to 80% by mass, or 65% to 75% by mass. Furthermore, the number of stages in which the slurry is diluted (the number of times the liquid medium is added) before the water-dispersible polymer is added may be, for example, 2 to 7 stages, 3 to 6 stages, or 4 to 6 stages.

[0080] In the above steps of this production example, the nonvolatile content concentration of the slurry immediately before the final addition of the water-dispersible polymer and the liquid medium may be, for example, 45% by mass to 65% by mass, 50% by mass to 60% by mass, or 52% by mass to 58% by mass. The nonvolatile content concentration of the electrode slurry obtained by these steps may be, for example, 45% by mass to 65% by mass, 50% by mass to 60% by mass, or 52% by mass to 58% by mass.

[0081] Here, the liquid medium added at each stage is preferably water or a liquid containing water. The water-containing liquid preferably consists of one phase (is not phase-separated). The water content of the water-containing liquid is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and may be 98% by mass or more.

[0082] When the electrode slurry obtained by the procedure described in this example is used, the number of through-flow paths in the electrode active material layer formed tends to be increased. Note that the method for producing the electrode slurry is not limited to the above production example.

[0083] Further, an example of a method for manufacturing an electrode includes the steps of: visualizing pores in the electrode active material layers in three-dimensional images obtained by X-ray CT scanning of electrode active material layers of a plurality of nonaqueous secondary battery electrodes having electrode active material layers prepared with varying compositions on a current collector, and detecting the number of through-flow paths per unit area reaching a depth of 50 μm from the surface of each electrode active material layer; predicting the number of through-flow paths per unit area in an electrode active material layer of a hypothetical composition based on the input composition of the electrode active material layer and the detected number of through-flow paths per unit area; determining a composition of the electrode active material layer such that the predicted number of through-flow paths per unit area is equal to or greater than a predetermined value; and forming an electrode active material layer of the determined composition on a current collector.

[0084] In the above manufacturing method, the number of through-channels is detected by the above-mentioned method. Then, the composition of the electrode active material layer, which is the object for which the number of through-channels has been detected, is input separately, and the number of through-channels per unit area in an electrode active material layer of a hypothetical composition is predicted based on the number of through-channels and the composition in the electrode active material layer. For example, by checking how the number of through-channels per unit area changes when only the type of binder in the electrode active material layer is changed and the other compositions are fixed, the number of through-channels can be predicted based on the characteristics of the binder type (e.g., the type and number of functional groups).

[0085] 3 and 4 are colored images of the surface of the electrode active material layer when the binder type is changed. FIG. 3 is a colored image when the binder (A1) obtained in Synthesis Example 1 of the Examples is used, and FIG. 4 is a colored image when the binder (A2) obtained in Synthesis Example 2 of the Examples is used. A comparison of FIG. 3 and FIG. 4 reveals that the electrode active material layer using the binder (A1) has a larger number of through-flow channels per unit area. In other words, it is presumed that the electrode active material layer using the binder (A1) allows the electrolyte to more easily penetrate the entire electrode active material layer, has excellent ion diffusibility, and lowers the internal resistance of the electrode.

[0086] After selecting a suitable binder type, the number of through-flow paths may be detected for electrode active material layers in which the content of each component is changed for that binder type, and the number of through-flow paths may be predicted for an electrode active material layer having a hypothetical content composition.

[0087] By this operation, the composition of the electrode active material layer is determined so that the predicted number of through-flow paths per unit area is equal to or greater than a predetermined value. When the electrode active material layer having the determined composition is formed on the current collector, the number of through-flow paths is 3.50 / μm. ２ A negative electrode having the above electrode active material layer can be obtained.

[0088] <Non-aqueous secondary battery> The non-aqueous secondary battery of the present disclosure includes the electrode of the present disclosure. Below, a lithium ion secondary battery will be described as a preferred example of the non-aqueous secondary battery of the present disclosure, but the configuration of the battery is not limited to that described here. The non-aqueous secondary battery of the present disclosure includes a positive electrode and a negative electrode. The electrode of the present disclosure may be a positive electrode, a negative electrode, or both a positive electrode and a negative electrode. The non-aqueous secondary battery of the present disclosure may further include an electrolyte solution and, if necessary, components such as a separator. These are housed in an exterior housing.

[0089] 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.

[0090] The electrolyte can be an alkali metal salt, and can be appropriately selected depending on the type of electrode active material. ４ , LiBF ６ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２Examples of the electrolyte include lithium carboxylate, lithium cations of N, and aliphatic carboxylates. Other alkali metal salts can also be used as the electrolyte.

[0091] 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).

[0092] 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.

[0093] 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.

[0094] [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 Dai-ichi Kogyo Seiyaku Co., Ltd., and is a compound represented by the above formula (2).

[0095] 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.

[0096] 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 to 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. Rongalit SFS, used as the polymerization initiator, was manufactured by Sumitomo Seika Chemicals Co., Ltd.

[0097] Through this process, a binder composition of Synthesis Example 1 was obtained as an emulsion containing the binder (A1).

[0098] 1-2. Synthesis Example 2 The type and amount of monomer (a) shown in Synthesis Example 2 in Table 1 was mixed with 200 parts by mass of water and emulsified to prepare a monomer emulsion.

[0099] 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.

[0100] 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 to the pressure vessel all at once, 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.

[0101] 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).

[0102] [1-3. Measurement of nonvolatile content concentration] 1 g of each of the emulsions obtained in Synthesis Examples 1 and 2 was weighed into a 5 cm diameter aluminum dish and dried at 105°C for 1 hour while circulating air in a dryer at 1 atmosphere (1013 hPa), and the mass of the remaining components was measured to determine the nonvolatile content concentration (mass%). The measured values ​​of the nonvolatile content concentrations of the emulsions obtained in Synthesis Examples 1 and 2 are shown in Table 1.

[0103] [1-4. Measurement of Glass Transition Point] 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), and the remaining components were removed and placed in a sample pan for DSC measurement. The DSC measurement was performed using an EXSTAR DSC / SS7020 manufactured by 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 DSC was taken as the glass transition point (°C) of the binder polymer (A1) or binder polymer (A2). The measured values ​​of the glass transition points of the binder polymer (A1) and binder polymer (A2) are shown in Table 1.

[0104]

[0105] <2. Negative Electrode Slurry> [2-1. Preparation of Negative Electrode Slurry] In each Example and Comparative 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, electrode active material (negative electrode active material), and water were first kneaded together, and then diluted and kneaded stepwise to achieve non-volatile content concentrations of 69 mass%, 67 mass%, 65 mass%, 63 mass%, 61 mass%, and 56 mass%. The resulting negative electrode slurry with a concentration of 56 mass% was then kneaded with binder and water to obtain a negative electrode slurry with a non-volatile content of 55 mass%. 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, was the above-mentioned amount. 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.

[0106] As the binder, the binder (A1) synthesized in Synthesis Example 1 or the binder (A2) synthesized in Synthesis Example 2 was used.

[0107] 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.

[0108] The following graphite was used as the negative electrode active material: Artificial graphite A: particle diameter (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 diameter (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

[0109] [2-2. Nonvolatile 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 the mixture was dried at 130 ° C. for 1 hour under 1 atmosphere (1013 hPa) with air circulating in a dryer. The mass of the remaining components was measured, and the nonvolatile content (mass%) was determined. The nonvolatile content of the electrode slurries prepared in each Example and Comparative Example is shown in Table 2.

[0110] <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 so that the weight per side after drying was 12.5 mg / cm. ２ The coating was applied so that

[0111] 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. The thickness of the negative electrode active material layer on the negative electrode sheet at this stage (before pressing) was 130 μm per side in each of the Examples and Comparative Examples.

[0112] The obtained negative electrode sheet was pressed with a roll press (manufactured by Thank Metal Co., Ltd., press load 5 t, roll width 7 cm). The thickness of the negative electrode active material layer on the negative electrode sheet after pressing was 75 μm per side in each of the Examples and Comparative Examples.

[0113] 3-2. Evaluation of Flow Channels in the Negative Electrode Active Material Layer The morphology of the flow channels in the negative electrode active material layer was evaluated as follows. The pressed negative electrode sheet was cut into a size of 1 mm x 30 mm to prepare a test piece. A three-dimensional image of the negative electrode active material layer in the test piece was obtained under the above-mentioned conditions using a microfocus X-ray CT system SMX-160CTS manufactured by Shimadzu Corporation.

[0114] 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. According to this porosity, the through-flow channels of the three-dimensional image were colored by computer processing to obtain a colored image. Then, the number of through-flow channels per unit area was measured within the above analysis range using three-dimensional image analysis software (ExFact VR and ExFact Analysis for Porous Particles, manufactured by Japan Visual Science Co., Ltd.). The results are shown in Table 2.

[0115] In addition, 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 were measured using three-dimensional image analysis software (ExFact VR and ExFact Analysis for Porous Particles, manufactured by Japan Visual Science Co., Ltd.), and the tortuosity was calculated using the above formula (1). The tortuosity of all through-flow passages within the above analysis range was analyzed, and the average tortuosity obtained is shown in Table 2.

[0116] Figure 1 shows X-ray CT images of the surfaces of the negative electrode active material layers in Example 1 and Comparative Example 1. 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. Figure 2 also shows SEM photographs of the surfaces of the negative electrode active material layers in Example 1 and Comparative Example 1. However, the SEM photographs in Figure 2 were taken at different locations than the X-ray CT images in Figure 1.

[0117] [3-3. Measurement of electrode density] A copper foil having a thickness of 10 μm used as a negative electrode current collector was cut into a size of 52 mm × 42 mm (= 5.2 cm × 4.2 cm), and the mass m ０ In each example and comparative example, the mass m of the negative electrode (52 mm × 42 mm = 5.2 cm × 4.2 cm) before the conductive tab was attached was measured. １ The mass of the negative electrode m １ and the mass of the copper foil piece m ０ The difference between the areas of the copper foil piece and the negative electrode is divided by the area of ​​the copper foil piece and the negative electrode to obtain the weight M [mg / cm ２ The basis weight M [mg / cm 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), to obtain the electrode density [g / cm ３ The true density of each of the artificial graphite A, artificial graphite B, and natural graphite used as the electrode active material was calculated to be 2.2 g / cm. ３ The filling rate of the electrode active material in the electrode active material layer was calculated as follows.

[0118] 4. Lithium-ion secondary battery 4-1. Battery fabrication Lithium-ion secondary batteries were fabricated using the negative electrodes of each example and comparative example. In the following description, the fabrication of the negative electrodes 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.

[0119] LiNi as the positive electrode active material ０．６ Mn ０．２ Co ０．２ O ２ 94 parts by mass of the above, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder were mixed, and 50 parts by mass of N-methylpyrrolidone was added and further mixed to prepare a positive electrode slurry.

[0120] The positive electrode slurry was applied to both sides of a 15 μm-thick aluminum foil (positive electrode current collector) by a direct roll coating 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.

[0121] 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 3 t, roll width 7 cm) to obtain a positive electrode sheet in which a positive electrode active material layer was 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.

[0122] A separator (made of polyethylene, 25 μm) made of a polyolefin-based porous film was interposed between the positive electrode and the negative electrode, and the positive electrode active material layer and the negative electrode active material layer were housed in an aluminum laminate exterior (battery pack) so that they faced each other. An electrolyte was injected into this exterior, vacuum impregnation was performed, and the battery was packed with a vacuum heat sealer to prepare a lithium-ion secondary battery for evaluation. The electrolyte was a mixture of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) = 30 / 50 / 20 (volume ratio) and LiPF ６ The solution was prepared by mixing 99 parts by mass of a solution in which the above compound was dissolved at 1.0 mol / L with 1 part by mass of vinylene carbonate.

[0123] [4-2. Measurement of Internal Resistance] The internal resistance (DCR (Ω)) of the lithium ion secondary battery was measured under conditions of 25°C according to the following procedure. First, the state of charge was set to 50% of the initial capacity (SOC 50%) 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 SOC 50% was determined from the relationship between these four current values ​​(values ​​over 1 second) and voltage.

[0124]

[0125] <5. Evaluation Results> A negative electrode active material and a binder were included, and the number of through-flow paths was 3.50 / μm. ２ or more, and the density is 1.20 g / cm ３ The negative electrode active material layers of Examples 1 to 3 each have a through-flow path number of 3.50 / μm. ２ The internal resistance was lower than that of the negative electrode active material layers of Comparative Examples 1 to 3. The negative electrode active material layers of Examples 1 to 3 had the same electrode density as the negative electrode active material layers of Comparative Examples 1 to 3, and were able to maintain a large charge / discharge capacity as electrodes and batteries.

[0126] The disclosure of Japanese Patent Application No. 2024-102345 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated by reference into this specification to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An electrode active material layer containing an electrode active material, wherein the thickness of the electrode active material layer is 50 μm or more, and the number of through-flow paths per unit area reaching a depth of 50 μm from the surface of the electrode active material layer, detected by processing data obtained by X-ray CT scanning of the electrode active material layer, is 3.50 paths / μm. ２ or more, and the density of the electrode active material layer is 1.20 g / cm ３ This completes the electrode active material layer.

2. The electrode active material layer according to claim 1, wherein the thickness of the electrode active material layer is 60 μm or more.

3. The electrode active material layer according to claim 1, wherein the electrode active material layer contains 80 mass % or more of the electrode active material.

4. The electrode active material layer according to claim 1, wherein a packing ratio, which is the ratio of the electrode density of the electrode active material layer to the true density of the electrode active material, is 50% or more.

5. The electrode active material layer according to claim 1, wherein the electrode active material contains 50 mass % or more of graphite.

6. The electrode active material layer according to claim 1, wherein the through-flow passage has a tortuosity of 3.00 or less, as 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 electrode active material layer to the opening of the through-flow passage on the other surface.) 7. A non-aqueous secondary battery electrode comprising a current collector and the electrode active material layer according to any one of claims 1 to 6.

8. A non-aqueous secondary battery comprising the electrode according to claim 7.

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