Nonaqueous secondary battery electrode and nonaqueous secondary battery

Abstract

This nonaqueous secondary battery electrode includes: a current collector; and an electrode active material layer provided on the current collector and having a thickness of 100 µｍ or more. The electrode active material layer contains 80 mass% or more of an electrode active material. In measurements by a surface cutting test (SAICAS) under specific conditions, when an electrode strength at a depth of t [μｍ] from the surface of the electrode active material layer is P(t) [kN / m], P(30) is 0.100 kN / m or more, and the ratio of P(90) to P(30) [P(90) / P(30)] is 0.60 or more.

Description

Non-aqueous secondary battery electrode and non-aqueous secondary battery

[0001] The present disclosure relates to a non-aqueous secondary battery electrode and a non-aqueous secondary battery.

[0002] A non-aqueous secondary battery includes, 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 solution. A non-aqueous secondary battery is a secondary battery in which ions move between the positive electrode and the negative electrode to charge and discharge the battery.

[0003] A typical example of a non-aqueous secondary battery is a lithium-ion secondary battery. Non-aqueous secondary batteries are used as power sources for notebook computers, mobile phones, power tools, electronic devices, communication devices, and the like due to their compact size and lightweight design. Recently, they have also been used in electric vehicles and hybrid vehicles due to their environmentally friendly application. In this context, there has been a strong demand for non-aqueous secondary batteries with higher output, higher capacity, and longer life.

[0004] A commonly used electrode for a non-aqueous secondary battery is one in which an electrode active material layer is formed on a metal current collector. The current collector is typically made of a metal foil such as aluminum or copper. The electrode active material layer contains an electrode active material, a binder, and, if necessary, a conductive additive. The electrode 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] In the process of producing an electrode for a non-aqueous secondary battery, for example, a slurry (electrode slurry) in which an electrode binder and an electrode active material are dissolved or dispersed in water is applied to the surface of a current collector and dried to form an electrode active material layer on the current collector.

[0006] For example, Patent Document 1 describes a slurry for lithium ion secondary battery electrodes obtained using a binder for lithium ion secondary battery electrodes, an electrode active material, and carboxymethyl cellulose. It also describes that the binder for lithium ion secondary battery electrodes is obtained by emulsion polymerization of an ethylenically unsaturated monomer containing styrene, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and an internal crosslinking agent. Patent Document 2 describes a secondary battery electrode having an electrode layer containing at least one polymer selected from the group consisting of a styrene-butadiene copolymer and a copolymer obtained from a (meth)acrylic acid ester and a vinyl monomer having an acid component, and a specific nonionic surfactant.

[0007] Patent Document 3 discloses an electrode active material layer including an intermediate layer disposed between an electrode active material layer and an electrode current collector, the electrode active material layer including a first electrode active material layer in contact with the intermediate layer, and a second electrode active material layer disposed on the first electrode active material layer and including a second electrode active material, the first electrode active material layer having a vertical relative bonding strength (F) measured by a surface and interfacial measuring analysis system (SAICAS) from a first point spaced 5% apart from one surface of the first electrode active material layer in the direction of the electrode current collector to a second point spaced 5% apart from the surface of the first electrode active material layer facing the electrode current collector, relative to the total thickness of the first electrode active material layer. ＶＲ The second electrode active material layer has a first rate of change in vertical relative binding strength (FVR) relative to the depth from a third point 5% away from the surface of the second electrode active material layer in the direction of the first electrode active material layer to a fourth point 5% away from the surface of the first electrode active material layer, per total thickness of the second electrode active material layer, as measured by SAICAS, and the first rate of change and the second rate of change are within a predetermined range.

[0008] JP 2011-243464 A JP 2014-239070 A Japanese Patent No. 7359883 A

[0009] Non-aqueous secondary batteries are required to be smaller and have larger capacities. To meet this demand, measures include thickening the electrode active material layer and increasing the content of the electrode active material in the electrode active material layer. However, as the electrode active material layer becomes thicker, the internal resistance of the battery tends to increase. This is thought to be due to an increase in the distance from the surface of the electrode active material layer to the current collector. It is also thought that as the electrode active material layer becomes thicker, the conductive path between the surface of the electrode active material layer and the current collector becomes more likely to be broken. Increasing the content of the electrode active material also tends to increase the internal resistance of the battery. One possible cause of this is a lack of binder in the electrode active material layer, which prevents sufficient formation of a conductive path within the electrode active material layer, resulting in increased electrical resistance (electrode resistance) within the electrode active material layer and between the electrode active material layer and the current collector. Therefore, the present disclosure aims to provide a non-aqueous secondary battery electrode and a non-aqueous secondary battery that can suppress an increase in electrode resistance even when the electrode active material layer has a high content of electrode active material and a thick electrode active material layer.

[0010] The present disclosure includes the following aspects: <1> A non-aqueous secondary battery electrode comprising: a current collector; and an electrode active material layer provided on the current collector and having a thickness of 100 μm or more, wherein the electrode active material layer contains 80 mass% or more of an electrode active material, and wherein, when measured by a surface cutting test (SAICAS) under the following conditions, where P(t) [kN / m] is the electrode strength at a depth t [μm] from the surface of the electrode active material layer, P(30) is 0.100 kN / m or more, and the ratio of P(90) to P(30) [P(90) / P(30)] is 0.60 or more. The conditions were as follows: measurement mode: constant speed mode; cutting edge material: borazon; cutting edge width: 1.0 mm; rake angle: 20°; clearance angle: 10°; electrode: a 20 mm x 20 mm square in plan view, with the electrode active material layer provided over the entire surface of one side of the current collector; and measurement was performed according to the following steps (1) to (4): (1) The tip of the cutting edge was brought into contact with the starting point on the surface of the electrode active material layer. The starting point was located 5 mm inward from one of the four outer edges of the electrode, and the center of the cutting edge in the width direction was on a center line equidistant from and parallel to two outer edges perpendicular to the first edge. (2) From the starting point, the cutting edge was moved along the center line toward the other edge opposite the first edge at a speed of 5 μm / sec, and in the depth direction at a speed of 0.5 μm / sec to a predetermined depth t [μm] from the surface of the electrode active material layer. (3) The tip of the cutting blade is moved 1000 μm along the center line toward the other side at a speed of 5 μm / sec while maintaining the depth t [μm]. At this point, the measurement is completed. (4) The horizontal force F per elapsed time from the start of the movement of the cutting blade Ｈ The horizontal force F in the step (3) is measured. ＨThe average value of these is defined as the electrode strength P(t). <2> The nonaqueous secondary battery electrode according to <1>, wherein the ratio [P(90) / P(30)] is 1.5 or less. <3> The nonaqueous secondary battery electrode according to <1> or <2>, wherein the ratio of P(60) to P(30) [P(60) / P(30)] is 0.80 or more. <4> The nonaqueous secondary battery electrode according to <3>, wherein the ratio [P(60) / P(30)] is 1.5 or less. <5> The nonaqueous secondary battery electrode according to any one of <1> to <4>, wherein the relationship between the ratio of P(60) to P(30) [P(60) / P(30)] and the ratio of P(90) to P(60) [P(90) / P(60)] satisfies the following formula: 0.90≦{P(90) / P(60)} / {P(60) / P(30)}≦1.1 <6> The nonaqueous secondary battery electrode according to any one of <1> to <5>, wherein the electrode active material contains 50 mass% or more of graphite. <7> The nonaqueous secondary battery electrode according to <6>, wherein the current collector contains copper as a main component. <8> The nonaqueous secondary battery electrode according to any one of <1> to <7>, wherein the electrode active material layer contains at least one selected from the group consisting of a water-dispersible polymer and a water-soluble polymer. <9> The nonaqueous secondary battery electrode according to <8>, wherein the electrode active material layer contains a water-dispersible polymer and a water-soluble polymer. <10> The nonaqueous secondary battery electrode according to <8> or <9>, wherein the water-soluble polymer has a weight-average molecular weight of 800,000 or more. <11> A nonaqueous secondary battery comprising the nonaqueous secondary battery electrode according to any one of <1> to <10>.

[0011] According to the present disclosure, it is possible to provide a nonaqueous secondary battery electrode and a nonaqueous secondary battery that can suppress an increase in electrode resistance even when the content of the electrode active material is high and the electrode active material layer is thick.

[0012] Hereinafter, nonaqueous secondary battery electrodes and nonaqueous secondary batteries will be described as embodiments of the present disclosure. 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 this 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 this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In this 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 area in which the layer exists is observed, as well as cases where the layer is formed over only a portion of the area.

[0013] 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))

[0014] <1. Nonaqueous Secondary Battery Electrode> A nonaqueous secondary battery electrode (hereinafter, the nonaqueous secondary battery electrode may be simply referred to as an electrode) according to the present disclosure comprises a current collector and an electrode active material layer provided on the current collector and having a thickness of 100 μm or more, wherein the electrode active material layer contains 80 mass% or more of an electrode active material, and wherein, as measured by a surface cutting test (SAICAS) under the following conditions, when the electrode strength at a depth t [μm] from the surface of the electrode active material layer is P(t) [kN / m], P(30) is 0.100 kN / m or more, and the ratio of P(90) to P(30), [P(90) / P(30)], is 0.60 or more.

[0015] The conditions were as follows: measurement mode: constant speed mode; cutting edge material: borazon; cutting edge width: 1.0 mm; rake angle: 20°; clearance angle: 10°; electrode: a 20 mm x 20 mm square in plan view, with the electrode active material layer provided over the entire surface of one side of the current collector; and measurement was performed according to the following steps (1) to (4): (1) The tip of the cutting edge was brought into contact with the starting point on the surface of the electrode active material layer. The starting point was located 5 mm inward from one of the four outer edges of the electrode, and the center of the cutting edge in the width direction was on a center line equidistant from and parallel to two outer edges perpendicular to the first edge. (2) From the starting point, the cutting edge was moved along the center line toward the other edge opposite the first edge at a speed of 5 μm / sec, and in the depth direction at a speed of 0.5 μm / sec to a predetermined depth t [μm] from the surface of the electrode active material layer. (3) The tip of the cutting blade is moved 1000 μm along the center line toward the other side at a speed of 5 μm / sec while maintaining the depth t [μm]. At this point, the measurement is completed. (4) The horizontal force F per elapsed time from the start of the movement of the cutting blade Ｈ The horizontal force F in the step (3) is measured. Ｈ The average value of the electrode strength is P(t).

[0016] [1-1. Current Collector] The current collector is preferably made of a metal, and preferably contains a metal such as iron, copper, aluminum, nickel, or stainless steel as its main component. When the nonaqueous secondary battery electrode is a negative electrode for a lithium-ion secondary battery, the current collector preferably contains copper as its main component. The phrase "containing metal A as its main 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 ratio, and cases where metal A is an alloy of two or more metals including metal A and metal A has the largest mass ratio. 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.

[0017] [1-2. Electrode active material layer] [1-2-1. Configuration of electrode active material layer] The thickness of the electrode active material layer is 100 μm or more, preferably 110 μm or more, and more preferably 120 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 170 μm or less, and even more preferably 150 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.

[0018] 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.

[0019] The electrode active material layer contains 80% by mass or more of the electrode active material, preferably 90% by mass or more, and 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.

[0020] 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.

[0021] The electrode active material layer preferably contains at least one selected from the group consisting of a water-dispersible polymer and a water-soluble polymer, and more preferably contains a water-dispersible polymer and a water-soluble polymer. 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.

[0022] 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.

[0023] Examples of materials that can be used as the water-dispersible polymer and the water-soluble polymer will be described in detail below.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Furthermore, the electrode active material layer may contain other components such as a conductive aid, a surfactant, and other additives.

[0028] [1-1-2. Electrode Strength by SAICAS Measurement of Electrode Active Material Layer] The electrode strength P(t) [kN / m] of the electrode active material layer is a value measured by SAICAS under the above conditions. As a SAICAS measurement device, for example, a SAICAS EN model manufactured by Daipla Wintes Co., Ltd. can be used. Measurement of electrode strength P(t) at different depths (t) from the surface of the electrode active material layer is performed by preparing individual electrodes. In step (3), the depth (t) from the surface of the electrode active material layer is kept constant, and the electrode strength P(t) at each depth (t) is measured. This makes it possible to confirm the difference between the electrode strength P(t) at a specific depth and the electrode strength P(t) at another specific depth. This method makes it possible to grasp the degree of uneven distribution of components in the depth direction of the electrode active material layer.

[0029] P(30) is 0.100 kN / m or more, preferably 0.130 kN / m or more, more preferably 0.150 kN / m or more, and even more preferably 0.172 kN / m or more. When P(30) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because the electrode active materials are firmly bonded together, forming a sufficient conductive path.

[0030] P(60) is preferably 0.090 kN / m or more, more preferably 0.120 kN / m or more, even more preferably 0.140 kN / m or more, and particularly preferably 0.155 kN / m or more. When P(60) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because the electrode active materials are firmly bonded together, forming a sufficient conductive path.

[0031] P(90) is preferably 0.080 kN / m or more, more preferably 0.110 kN / m or more, even more preferably 0.130 kN / m or more, and particularly preferably 0.140 kN / m or more. When the P(90) of the electrode active material layer is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because the electrode active materials are firmly bonded together, forming a sufficient conductive path.

[0032] The ratio of P(90) to P(30) [P(90) / P(30)] is 0.60 or more, preferably 0.70 or more, more preferably 0.80 or more, and even more preferably 0.88 or more. When the ratio [P(90) / P(30)] is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be reduced. This is thought to be because the electrode active materials are firmly bonded not only near the surface of the electrode active material layer but also in areas away from the surface of the electrode active material layer, and a sufficient conductive path is formed throughout the electrode active material layer.

[0033] The ratio [P(90) / P(30)] may be 1.5 or less, 1.2 or less, or 1.0 or less.

[0034] The ratio [P(90) / P(30)] may be 0.60 to 1.5, 0.70 to 1.2, 0.80 to 1.0, or 0.88 to 1.0.

[0035] The ratio of P(60) to P(30) [P(60) / P(30)] is preferably 0.80 or more, more preferably 0.85 or more, and even more preferably 0.90 or more. When the ratio [P(60) / P(30)] is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be further reduced. This is thought to be because the electrode active materials are firmly bonded not only near the electrode active material layer but also in areas away from the surface of the electrode active material layer, and a sufficient conductive path is formed throughout the electrode active material layer.

[0036] The ratio [P(60) / P(30)] may be 1.5 or less, 1.2 or less, or 1.0 or less.

[0037] The ratio [P(60) / P(30)] may be 0.80 to 1.5, 0.85 to 1.2, or 0.90 to 1.0.

[0038] The ratio of P(90) to P(60) [P(90) / P(60)] is preferably 0.75 or more, more preferably 0.85 or more, and even more preferably 0.90 or more. When the ratio [P(90) / P(60)] is within the above range, the electrode resistance within the electrode active material layer and between the electrode active material layer and the current collector tends to be further reduced. This is thought to be because the electrode active materials are firmly bonded not only near the electrode surface but also in areas away from the electrode surface, and a sufficient conductive path is formed throughout the electrode active material layer.

[0039] The ratio [P(90) / P(60)] may be 1.2 or less, 1.1 or less, or 1.0 or less.

[0040] The relationship between the ratio of P(60) to P(30) [P(60) / P(30)] and the ratio of P(90) to P(60) [P(90) / P(60)] is preferably 0.90≦{P(90) / P(60)} / {P(60) / P(30)}≦1.1, more preferably 0.95≦{P(90) / P(60)} / {P(60) / P(30)}≦1.07, and even more preferably 0.97≦{P(90) / P(60)} / {P(60) / P(30)}≦1.05. When the above relationship is satisfied, the rapid change in the binding strength between the electrode active materials tends to be suppressed with respect to the change in the position in the thickness direction within the electrode active material layer.

[0041] [1-2-3. 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.

[0042] 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.

[0043] 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.

[0044] When the electrode is a positive electrode, the electrode active material, i.e., the positive electrode active material, is a material having a nobler 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.

[0045] 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.

[0046] [1-2-4. Water-dispersible polymer] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] [1-2-5. Water-soluble polymer] The water-soluble polymer has a solubility in water of 10 g / 100 gH 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] [1-2-6. Relationship between the Structure of the Electrode Active Material Layer and P(t), etc.] When the thickness of the electrode active material layer is 100 μm or more and the content of the electrode active material in the electrode active material layer is 80 mass% or more, any method can be used to achieve a P(30) of 0.100 kN / m or more and a ratio [P(90) / P(30)] of 0.60 or more, and this can be achieved by combining the above-mentioned structures and components of the electrode active material layer. For example, the electrode active material layer may include at least one selected from the group consisting of water-dispersible polymers and water-soluble polymers, a water-soluble polymer having a weight-average molecular weight within the above range, a cellulose derivative as the water-soluble polymer, a water-dispersible polymer having a glass transition temperature Tg within the above range, or a combination thereof.

[0058] <2. Manufacturing Method of Non-Aqueous Secondary Battery Electrode> 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 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, considering the physical properties of the electrode slurry, such as viscosity, and drying properties, the doctor blade method, knife method, or extrusion method is preferred. Using these application methods tends to produce an electrode active material layer with a smooth surface and small thickness variation.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] Before or after cutting the electrode sheet, the electrode sheet may be pressed as needed, but it is preferable not to press it.

[0063] 3. Nonaqueous Secondary Battery The nonaqueous secondary battery of the present disclosure includes the nonaqueous secondary battery electrode of the present disclosure. A lithium-ion secondary battery will be described as a preferred example of the nonaqueous secondary battery of the present disclosure, but the battery configuration is not limited to that described here. The nonaqueous secondary battery of the present disclosure includes a positive electrode, a negative electrode, an electrolyte, and, if necessary, components such as a separator housed in an exterior body, and the above-described electrode is used for one or both of the positive electrode and the negative electrode.

[0064] [3-1. Electrolyte] It is preferable to use a non-aqueous liquid having ion conductivity as the electrolyte. Examples of the electrolyte include a solution in which an electrolyte is dissolved in an organic solvent and an ionic liquid, 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.

[0065] The electrolyte can be an alkali metal salt, and can be appropriately selected depending on the type of electrode active material, etc. The electrolyte can be LiClO 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 ) ２ Examples of the electrolyte include lithium carboxylate, lithium cations of N, and aliphatic carboxylates. Other alkali metal salts can also be used as the electrolyte.

[0066] 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).

[0067] [3-2. Exterior Body] The exterior body 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 type, button type, sheet type, cylindrical type, square type, and flat type.

[0068] 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.

[0069] <1. Synthesis of Water-Dispersible Polymers> [1-1. Synthesis Example 1] A monomer emulsion was prepared by mixing and emulsifying the types and amounts of monomers shown in Synthesis Example 1 in Table 1 with 200 parts by mass of water. Aqualon KH10 is a polymerizable surfactant, and is a polyoxyethylene-1-(allyloxymethyl) alkyl ether sulfate ester ammonium salt manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Next, a radical polymerization initiator of the type and amount shown in Synthesis Example 1 in Table 1 was each dissolved in 50 parts by mass of water to prepare an aqueous polymerization initiator solution.

[0070]

[0071] 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 polymerization initiator aqueous 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, yielding 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 radical polymerization initiator, was manufactured by Sumitomo Seika Chemicals Co., Ltd. This process yielded an emulsion containing a water-dispersible polymer (A1). The solubility of the water-dispersible polymer (A1) in water was 0.50 g / 100 gH. ２ It was below O.

[0072] [1-2. Synthesis Example 2] The types and amounts of monomers shown in Synthesis Example 2 in Table 1 were mixed with 200 parts by mass of water and emulsified to prepare a monomer emulsion. Next, the types and amounts of radical polymerization initiators shown in Synthesis Example 2 in Table 1 were dissolved in 50 parts by mass of water to prepare an aqueous polymerization initiator solution. 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 polymerization initiator solution were each added simultaneously to this pressure vessel, and the mixture was stirred at 60°C for 8 hours to perform emulsion polymerization, thereby obtaining an emulsion. The resulting 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: 1.325 parts by mass of ammonia, 3.975 parts by mass of water) and 130 parts by mass of water were added. This step yielded an emulsion containing the water-dispersible polymer (A2). The solubility of the water-dispersible polymer (A2) in water was 0.50 g / 100 gH. ２ It was below O.

[0073] [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.

[0074] [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.

[0075] <2. Negative Electrode Slurry> [2-1. Preparation of Negative Electrode Slurry] In each Example and Comparative Example, the types of water-dispersible polymer, cellulose derivative as water-soluble polymer, and electrode active material (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 negative electrode slurries. The amount of water added in this step was adjusted so that the total amount, including the water contained in the emulsion, was the amount shown in Table 2. The water-dispersible polymers used were the water-dispersible polymer (A1) synthesized in Synthesis Example 1 and the water-dispersible polymer (A2) synthesized in Synthesis Example 2. In all Examples and Comparative Examples, sodium carboxymethylcellulose (CMC-Na) with a degree of etherification of 0.70 and a weight-average molecular weight of 2,000,000 was used as the water-soluble polymer. The solubility of CMC-Na in water was 10 g / 100 g H ２ The electrode active material used in all Examples and Comparative Examples was artificial graphite (G49, manufactured by Jiangxi Zishen Technology Co., Ltd.).

[0076] [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.

[0077] <3. Negative Electrode> [3-1. Preparation of Negative Electrode] The negative electrode slurry was applied to one side of a 10 μm thick copper foil (negative electrode current collector) by the direct roll method. The amount of negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after drying, as described below, would be 130 μm per side. The negative electrode current collector to which the negative electrode slurry had been applied was transported through a 1.6 m long drying furnace set at the temperature shown in Table 2 at the speed shown in Table 2 and dried, thereby obtaining a negative electrode sheet in which a negative electrode active material layer was formed on the current collector. The obtained negative electrode sheet was cut into a size of 52 mm x 42 mm, and a conductive tab was attached to prepare a negative electrode.

[0078] [3-2. Various Measurements of Negative Electrode] [3-2-1. Measurement of Electrode Strength of Negative Electrode Active Material Layer (SAICAS Measurement)] Using the method described above, the electrode strengths P(30), P(60), and P(90) were measured at depths of 30 μm, 60 μm, and 90 μm from the surface of the electrode active material layer for each of the electrodes produced in Examples 1 to 5 and Comparative Examples 1 to 4. A SAICAS EN model manufactured by Daipla Wintes Co., Ltd. was used as the surface cutting tester.

[0079] [3-2-2. Measurement of Resistance] The resistance (mΩ cm) of the negative electrode active material layer was measured using an electrode resistance measurement system XF057 manufactured by Hioki E.E. ２ ) and the interface resistance (mΩ cm ２ ) was measured.

[0080]

[0081] <4. Evaluation Results> All of the electrodes according to Examples 1 to 5 have a current collector and an electrode active material layer having a thickness of 100 μm or more provided on the current collector. The electrode active material layer contains 80% by mass or more of an electrode active material. When measured by a surface cutting test (SAICAS), where P(t) [kN / m] is the electrode strength at a depth t [μm] from the surface of the electrode active material layer, P(30) is 0.100 kN / m or more, and the ratio of P(90) to P(30) [P(90) / P(30)] is 0.60 or more. All of these electrodes have low resistance of the negative electrode active material layer and low interfacial resistance between the negative electrode active material layer and the current collector. On the other hand, all of the electrodes according to Comparative Examples 1 to 4, in which the ratio [P(90) / P(30)] is less than 0.60, have high resistance of the negative electrode active material layer and high interfacial resistance between the negative electrode active material layer and the current collector. From the above, it can be said that a non-aqueous secondary battery electrode having a current collector and an electrode active material layer provided on the current collector and having a thickness of 100 μm or more, wherein the electrode active material layer contains 80 mass% or more of an electrode active material, and wherein, as measured by a surface cutting test (SAICAS), where P(t) [kN / m] is the electrode strength at a depth t [μm] from the surface of the electrode active material layer, P(30) is 0.100 kN / m or more, and the ratio of P(90) to P(30) [P(90) / P(30)] is 0.60 or more, has low resistance of the negative electrode active material layer and low interfacial resistance between the negative electrode active material layer and the current collector.

[0082] The disclosure of Japanese Patent Application No. 2024-089279 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference 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. A non-aqueous secondary battery electrode comprising: a current collector; and an electrode active material layer provided on the current collector and having a thickness of 100 μm or more, wherein the electrode active material layer contains 80 mass% or more of an electrode active material; and, when measured by a surface cutting test (SAICAS) under the following conditions, where P(t) [kN / m] is the electrode strength at a depth t [μm] from the surface of the electrode active material layer, P(30) is 0.100 kN / m or more; and the ratio of P(90) to P(30) [P(90) / P(30)] is 0.60 or more. The conditions were as follows: measurement mode: constant speed mode; cutting edge material: borazon; cutting edge width: 1.0 mm; rake angle: 20°; clearance angle: 10°; electrode: a 20 mm x 20 mm square in plan view, with the electrode active material layer provided over the entire surface of one side of the current collector; and measurement was performed according to the following steps (1) to (4): (1) The tip of the cutting edge was brought into contact with the starting point on the surface of the electrode active material layer. The starting point was located 5 mm inward from one of the four outer edges of the electrode, and the center of the cutting edge in the width direction was on a center line equidistant from and parallel to two outer edges perpendicular to the first edge. (2) From the starting point, the cutting edge was moved along the center line toward the other edge opposite the first edge at a speed of 5 μm / sec, and in the depth direction at a speed of 0.5 μm / sec to a predetermined depth t [μm] from the surface of the electrode active material layer. (3) The tip of the cutting blade is moved 1000 μm along the center line toward the other side at a speed of 5 μm / sec while maintaining the depth t [μm]. At this point, the measurement is completed. (4) The horizontal force F per elapsed time from the start of the movement of the cutting blade Ｈ The horizontal force F in the step (3) is measured. Ｈ The average value of the electrode strength is P(t).

2. The non-aqueous secondary battery electrode according to claim 1, wherein the ratio [P(90) / P(30)] is 1.5 or less.

3. The non-aqueous secondary battery electrode according to claim 1, wherein the ratio of P(60) to P(30) [P(60) / P(30)] is 0.80 or more.

4. The non-aqueous secondary battery electrode according to claim 3, wherein the ratio [P(60) / P(30)] is 1.5 or less.

5. The nonaqueous secondary battery electrode according to claim 1, wherein the ratio of P(60) to P(30) [P(60) / P(30)] and the ratio of P(90) to P(60) [P(90) / P(60)] satisfy the following formula: 0.90≦{P(90) / P(60)} / {P(60) / P(30)}≦1.1 6. The non-aqueous secondary battery electrode according to claim 1, wherein the electrode active material contains 50 mass % or more of graphite.

7. The non-aqueous secondary battery electrode according to claim 6, wherein the current collector contains copper as a main component.

8. The non-aqueous secondary battery electrode according to claim 1, wherein the electrode active material layer contains at least one selected from the group consisting of water-dispersible polymers and water-soluble polymers.

9. The non-aqueous secondary battery electrode according to claim 8, wherein the electrode active material layer contains a water-dispersible polymer and a water-soluble polymer.

10. The non-aqueous secondary battery electrode according to claim 8, wherein the weight-average molecular weight of the water-soluble polymer is 800,000 or more.

11. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to any one of claims 1 to 10.

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