Electrode binder, electrode, lithium ion secondary battery, and method for manufacturing electrode

Abstract

One embodiment of the present invention relates to an electrode binder, an electrode, a lithium ion secondary battery or a method for producing an electrode; and the electrode binder contains ultra high molecular weight olefin polymer fine particles (A) that satisfy the requirements (i) to (iii) described below.　(i) The limiting viscosity (η) as measured in a decalin solution at 135°C is within the range of 5 to 50 dl / g. (ii) The average particle diameter d50 in the mass-based particle size distribution as determined by a Coulter counter method is within the range of 1 to 50 µm. (iii) Not less than 50% by mass of the ultra high molecular weight olefin polymer fine particles (A) passes through a mesh screen with openings of 45 μm.

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an electrode binder, an electrode, a lithium ion secondary battery, or a method for manufacturing an electrode. [Background technology]

[0002] Lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, making them suitable for use in mobile phones, laptops, etc. In recent years, as demand for and applications of lithium-ion secondary batteries have expanded, there has been a demand for improved performance, such as stability, lower resistance, and larger capacity, as well as environmental considerations and cost improvements in the manufacturing of lithium-ion secondary batteries.

[0003] A widely known method for manufacturing electrodes for lithium-ion secondary batteries is the wet method, in which a binder resin is dissolved or dispersed in a solvent, and an active material and a conductive additive are dispersed therein to form a slurry, which is then applied to the surface of a current collector, and the solvent is then volatilized. Also known is a dry method for producing an electrode, in which powder containing an active material is compression-molded using a powder rolling machine to produce a rolled sheet such as an electrode sheet.

[0004] As an example of a method for manufacturing an electrode by a dry method, Patent Document 1 discloses a method for manufacturing an anode in which lithium ions are pre-doped into the anode, thereby making it possible to control lithium metal plating and gas generation. Furthermore, for example, Patent Document 2 discloses a method for improving the charge / discharge capacity as a battery performance by optimizing the powder characteristics of the positive electrode active material and the mixing process during the production of the positive electrode material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2019-508896 [Patent Document 2] Japanese Patent Publication No. 2020-202159 Summary of the Invention

[0006] In wet processes, when a solvent is used as a binder dispersion medium, a process for volatilizing unnecessary solvent is required. This not only complicates the process but also raises safety and environmental concerns. Furthermore, the amount of slurry applied is affected by factors such as the viscosity of the solvent and film thickness, which requires complex parameter management, making it difficult to easily prepare electrode materials with the desired composition. Therefore, a safe and easy method for preparing electrodes is desired.

[0007] One embodiment of the present invention provides an electrode binder that can be used to fabricate an electrode by a dry method, and that can provide a battery with excellent charge / discharge capacity. Another embodiment of the present invention provides an electrode and a method for manufacturing the electrode that can provide a battery with excellent charge / discharge capacity. Another embodiment of the present invention provides a lithium-ion secondary battery with excellent charge / discharge capacity. [Means for solving the problem]

[0008] The means for solving the above problems include the following aspects.

[0009] <1> An electrode binder comprising ultra-high molecular weight olefin polymer fine particles (A) that satisfy the following requirements (i) to (iii): (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 5 to 50 dl / g; (ii) The average particle diameter d50 in the mass-based particle size distribution measured by the Coulter Counter method is in the range of 1 to 50 μm; (iii) 50% by mass or more passes through a 45 μm mesh sieve.

[0010] <2> The average particle diameter d50 of the ultra-high molecular weight olefin polymer fine particles (A) is in the range of 3 to 15 μm. <1> The electrode binder according to claim 1.

[0011] <3> The ultra-high molecular weight olefin polymer fine particles (A) are ethylene polymer fine particles. <1> or <2> The electrode binder according to claim 1.

[0012] <4> <1> ~ <3> 10. An electrode comprising the electrode binder according to any one of the above items 1 to 9 and an active material. <5> The electrode is obtained by the dry method. <4> The electrode according to claim 1.

[0013] <6> <4> or <5> A lithium ion secondary battery comprising the electrode according to claim 1 and an electrolyte.

[0014] <7> <1> ~ <3> and an active material to obtain an electrode composite material; producing an electrode comprising the electrode composite and a current collector; A method for manufacturing an electrode, comprising: [Effects of the Invention]

[0015] According to one embodiment of the present invention, there is provided an electrode binder that can be used to fabricate an electrode by a dry method, and that can provide a battery with excellent charge / discharge capacity. According to another embodiment of the present invention, there is provided an electrode and a method for manufacturing an electrode that can provide a battery with excellent charge / discharge capacity. According to another embodiment of the present invention, there is provided a lithium ion secondary battery with excellent charge / discharge capacity. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, the term "polymer" is a concept that includes homopolymers and copolymers. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. In this specification, when a numerical range is indicated by "to", the units written before or after the range indicate the same units unless otherwise specified. As used herein, a combination of two or more preferred embodiments is a more preferred embodiment.

[0017] <Electrode binder> An electrode binder according to one embodiment of the present invention (hereinafter also referred to as "the binder") contains ultra-high molecular weight olefin polymer fine particles (A) (hereinafter also referred to as "particles (A)") that satisfy the following requirements (i) to (iii): (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 5 to 50 dL / g. (ii) The average particle diameter d50 in the mass-based particle size distribution measured by the Coulter Counter method is in the range of 1 to 50 μm. (iii) 50% by mass or more passes through a 45 μm mesh sieve

[0018] By including particles (A) that satisfy the above requirements, the present binder allows electrodes to be produced by a dry process, and a battery with excellent charge / discharge capacity can be obtained. The reason for this is not clear, but is presumed to be as follows. When an electrode is produced by a dry process, the electrode-forming material (electrode composite material) may be pressed. The particles (A) contained in the binder have an intrinsic viscosity [η] within the above range, so that even when the particles (A) are in a molten state during pressing, they are less likely to flow from the electrode and can maintain their particle shape. This improves adhesion to the active material and prevents them from falling off the electrode. The particles (A) contained in this binder have an average particle diameter d50 within the above range and contain a small amount of coarse particles, which improves the dispersibility of active materials and suppresses the occurrence of electrical defects. Furthermore, it is possible to ensure a space in the electrode where lithium ions can be stably absorbed and released. As a result, the conductivity of the (lithium ion secondary) battery can be ensured. The particles (A) contained in the binder are made of an olefin polymer, and therefore have excellent resistance to solvents such as electrolytic solutions and excellent electrical properties.

[0019] <Ultra-high molecular weight olefin polymer particles (A)> The particles (A) satisfy the following requirements (i) to (iii). The particles (A) used as a raw material for the binder may have the following physical properties (including the average particle diameter d50, etc.) as follows. The particles (A) used in the present binder may be of one type or two or more types.

[0020] Requirement (i): The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 5 to 50 dl / g. When the intrinsic viscosity is within the above range, the molten material is less likely to flow from the electrode and can maintain its particle shape, which is preferable because it can improve adhesion to the active material, etc., facilitate the production of a battery with excellent charge / discharge capacity, and enable the production of an electrode by a dry process. From the above viewpoint, the intrinsic viscosity [η] of the particles (A) is preferably 5 to 40 dl / g, more preferably 5 to 30 dl / g, still more preferably 5 to 27 dl / g, and particularly preferably 10 to 27 dl / g.

[0021] Requirement (ii): The average particle diameter d50 in the mass-based particle size distribution according to the Coulter counter method is in the range of 1 to 50 μm. When the average particle diameter d50 is within the above range, the dispersibility with the active material and the like is improved, thereby preventing the particles from falling off from the electrode, and furthermore, a space in the electrode where lithium ions can be stably absorbed and desorbed can be secured, which is preferable because it makes it possible to easily obtain a battery with excellent charge / discharge capacity and to prepare an electrode by a dry method. From this viewpoint, the average particle size d50 is preferably 35 μm or less, more preferably 20 μm or less, even more preferably 15 μm or less, particularly preferably 13 μm or less, and preferably 3 μm or more. Furthermore, the upper limit of the average particle diameter d50 is preferably 15 μm, more preferably 12 μm, even more preferably 10 μm, and particularly preferably 8 μm. The lower limit of the average particle diameter d50 is preferably 1 μm, more preferably 3 μm. The range of the average particle diameter d50 is preferably 1 to 12 μm, more preferably 1 to 10 μm, even more preferably 1 to 8 μm, and particularly preferably 3 to 8 μm. When the average particle diameter d50 is within the above range, a larger amount of binder can penetrate between particles of the active material, etc., and the binding strength with the active material is increased even with a small amount of binder, so that the desired effect can be achieved even with a reduced amount of binder used. Therefore, the amount of the active material, etc. in the electrode can be increased, and as a result, a battery with excellent battery performance can be easily obtained. Furthermore, when the average particle diameter d50 of the particles (A) is approximately the same as the particle diameters of the positive electrode active material and the negative electrode active material described below, the positive electrode active material and the negative electrode active material tend to be less likely to fall off. The average particle diameter d50 of the particles (A) means the average primary particle diameter. The average particle diameter d50 is the value at which the integrated value of the particle size distribution is 50 mass % when the mass-based particle size distribution is measured by the Coulter counter method. Specifically, it is determined by the measurement method described in the Examples.

[0022] Requirement (iii): 50% by mass or more passes through a 45 μm mesh sieve. The particles (A) are those that pass through a 45 μm mesh sieve (JIS Z 8801) using a vibrating sieve or ultrasonic vibrating sieve, with 50% by mass or more of the particles passing through a 45 μm mesh sieve. If the amount passing through the 45 μm mesh sieve is 50% by mass or more of the total mass of the particles (A), a battery with excellent charge / discharge capacity can be easily obtained, and an electrode can be produced by a dry method, which is preferable.

[0023] The passing amount of 50% by mass or more means that the amount of coarse particles present is small. A small number of coarse particles is considered preferable because the amount of active material and the like retained by the particles (A) increases. Furthermore, a small number of coarse particles tends to reduce the occurrence of electrical defects and suppress a decrease in the capacity of the resulting battery. As a result, a battery with excellent charge / discharge capacity can be easily obtained, which is considered preferable. From this viewpoint, the passing amount of the particles (A) is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0024] Examples of the particles (A) include homopolymer particles such as polyethylene, polypropylene, poly-1-butene, and poly-4-methyl-1-pentene; and copolymer particles made from at least two α-olefins selected from ethylene, propylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0025] The particles (A) are preferably ethylene polymer fine particles (eg, ethylene homopolymer fine particles, copolymer fine particles of ethylene and one or more α-olefins), and particularly preferably ethylene homopolymer fine particles. Ethylene-based polymers have a lower melting point than, for example, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), and therefore can maintain their binding strength with active materials and the like without requiring high temperatures during electrode fabrication. Furthermore, ethylene-based polymers have a higher surface free energy than PTFE, PVDF, and the like, and therefore have a higher affinity with active materials and a stronger binding strength with active materials and the like. From these perspectives, ethylene-based polymer microparticles are preferred.

[0026] The content of ethylene-derived structural units in the copolymer fine particles of ethylene and one or more α-olefins is preferably 50 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more, based on 100 mol of the total of all structural units constituting the copolymer.

[0027] The melt flow rate (MFR) of the particles (A) is preferably less than 1.0 g / 10 min, more preferably 0.5 g / 10 min or less, and more preferably 0.01 g / 10 min or more. The MFR is measured in accordance with JIS K 7210-1 (2014) under conditions of 190°C and a test load of 21.6 kg.

[0028] The method for producing the particles (A) is not particularly limited as long as the particles (A) satisfy the above requirements (i) to (iii). For example, the particles (A) can be produced by the methods disclosed in the following documents. (1) International Publication No. 2006 / 054696 (2) International Publication No. 2008 / 013144 (3) International Publication No. 2009 / 011231 (4) International Publication No. 2010 / 074073 (5) JP 2012-131959 A

[0029] The particles (A) may use only biomass-derived raw materials, only fossil fuel-derived raw materials, or both biomass-derived raw materials and fossil fuel-derived raw materials as their raw materials (e.g., monomers such as ethylene and α-olefins). Biomass-derived feedstocks are feedstocks derived from any (renewable) natural raw material and its residues, such as plant or animal origin, including fungi, yeast, algae and bacteria, and are used for example to produce carbon. 14 C isotope 1×10 -12 and has a biomass carbon concentration (unit: pMC) of about 100 pMC as measured in accordance with ASTM D6866. Biomass-derived raw materials (e.g., monomers such as ethylene and α-olefins) can be obtained, for example, by conventionally known methods. It is preferable that the particles (A) contain structural units derived from biomass-derived raw materials from the viewpoint of reducing environmental load (mainly greenhouse gas emissions). Regarding particles (A), if the production conditions of particles (A), such as the polymerization catalyst, polymerization process, and polymerization temperature, are the same, even if the particles (A) are (co)polymers made from biomass-derived raw materials, 14 C isotope 1×10 -12 ~10 -14 Other than the proportion of biomass-derived materials, the molecular structure is the same as that of (co)polymers made from fossil fuel-derived materials. Therefore, it is believed that the performance of (co)polymers containing biomass-derived materials is the same as that of (co)polymers made from fossil fuel-derived materials.

[0030] The content of particles (A) in the binder is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 97% by mass or more, from the viewpoints that a battery with excellent charge / discharge capacity can be easily obtained and that the electrode can be easily produced by a dry method. The upper limit of the content is preferably 100% by mass.

[0031] <Other ingredients> The binder may further contain other components in addition to the particles (A). The other components are not particularly limited and include conventionally known components, such as olefin polymer particles other than particles (A), polyvinyl acetate, polymethyl methacrylate, carboxymethyl cellulose (CMC), nitrocellulose, fluororesin, and rubber particles. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of the rubber particles include styrene-butadiene rubber (SBR) particles and acrylonitrile rubber particles. The other components may each be used alone or in combination of two or more.

[0032] The content of the other components in the present binder is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. The content of olefin polymer particles other than the particles (A) in the binder is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less. It is particularly preferable that the present binder does not contain the other components (the content of the other components in the present binder is particularly preferably 0 mass %).

[0033] The raw materials for the other components may be biomass-derived raw materials only, fossil fuel-derived raw materials only, or both biomass-derived raw materials and fossil fuel-derived raw materials. It is preferable that the other components contain structural units derived from biomass-derived raw materials from the viewpoint of reducing environmental load (mainly greenhouse gas emissions).

[0034] ≪Electrode≫ An electrode according to one embodiment of the present invention preferably contains the binder and an active material. Since the electrode contains the present binder, it can be produced by a dry method, and a battery with excellent charge / discharge capacity can be easily obtained. The electrode is preferably an electrode obtained by a dry method, the method for producing the electrode being described later. The electrode may be a positive electrode or a negative electrode.

[0035] <Positive electrode> The positive electrode is preferably an electrode capable of absorbing and releasing lithium ions, and preferably includes the present binder, a conductive additive, and a positive electrode active material, and more preferably includes a positive electrode mixture layer containing the present binder, the conductive additive, and the positive electrode active material, and a positive electrode current collector. In this case, the positive electrode mixture layer is provided on at least a portion of the surface of the positive electrode current collector.

[0036] The content of the binder in the positive electrode mixture layer is preferably 0.1 to 10 mass %, more preferably 0.1 to 4 mass %, relative to the total mass of the positive electrode mixture layer, from the viewpoint of achieving both the physical properties (e.g., electrolyte permeability, peel strength) of the positive electrode mixture layer and the battery performance. When the content of the present binder is 0.1 mass% or more, the adhesion of the positive electrode mixture layer to the positive electrode current collector and the binding of the positive electrode active materials to each other are further improved. When the content of the present binder is equal to or less than the upper limit, the amount of the positive electrode active material in the positive electrode mixture layer can be increased, and by using the positive electrode mixture layer, a battery with a large capacity can be easily obtained.

[0037] The thickness of the positive electrode mixture layer is not particularly limited and may be the same as that of a conventionally known positive electrode mixture layer, but is preferably 30 to 500 μm, more preferably 30 to 300 μm, and even more preferably 30 to 150 μm.

[0038] [Cathode active material] The positive electrode active material is preferably a material capable of absorbing and releasing lithium ions, and examples thereof include positive electrode active materials that are commonly used in lithium ion secondary batteries. The positive electrode active material may be used alone or in combination of two or more.

[0039] Examples of the positive electrode active material include: Oxides whose constituent metal elements are lithium (Li) and nickel (Ni); An oxide containing, as constituent metal elements, Li, Ni, and at least one metal element other than Li and Ni (e.g., a transition metal element, a typical metal element); Examples include:

[0040] When a metal element other than Li and Ni is contained, the metal element is preferably contained in an amount equivalent to or less than that of Ni in terms of the number of atoms. Examples of the metal elements other than Li and Ni include at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce.

[0041] The positive electrode active material preferably contains a lithium-containing composite oxide (hereinafter also referred to as "NCM") represented by the following formula (C1): When NCM is used as the positive electrode active material, an electrode having a high energy density per unit volume and excellent thermal stability can be easily produced.

[0042] LiNi a Co b Mn c O2...Formula (C1) [In formula (C1), a, b, and c each independently represent a number greater than 0 and less than 1, and the sum of a, b, and c is 0.99 to 1.00.]

[0043] A specific example of NCM is LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 is one example.

[0044] The positive electrode active material may contain a lithium-containing composite oxide (hereinafter also referred to as "NCA") represented by the following formula (C2).

[0045] Li t Ni (1-x-y) Co x Al y O2...Formula (C2) [In formula (C2), t is 0.95 or more and 1.15 or less, x is 0 or more and 0.3 or less, y is 0.01 or more and 0.2 or less, and the sum of x and y is less than 0.5.]

[0046] A specific example of NCA is LiNi 0.8 Co 0.15 Al 0.05 O2 is one example.

[0047] The content of the positive electrode active material in the positive electrode mixture layer is, for example, 10 to 99.9 mass %, preferably 30 to 99.0 mass %, more preferably 50 to 99.0 mass %, and particularly preferably 70 to 99.0 mass %, relative to the total mass of the positive electrode mixture layer.

[0048] [Conductive additive] The conductive additive is not particularly limited as long as it is a material other than the active material, and any known conductive additive can be used. The known conductive assistant is preferably a carbon material having electrical conductivity, and examples thereof include graphite, carbon black, conductive carbon fiber (e.g., carbon nanotube, carbon nanofiber, carbon fiber), and fullerene. The conductive assistant may be used alone or in combination of two or more kinds.

[0049] As the carbon black, commercially available products may be used. Examples of commercially available carbon black include Toka Black #4300, #4400, #4500, and #5500 (furnace black manufactured by Tokai Carbon Co., Ltd.), Printex L (furnace black manufactured by Degussa), Raven 7000, 5750, 5250, 5000ULTRA III, 5000ULTRA, Conductex SC ULTRA, Conductex 975ULTRA, and PUER. BLACK100, 115, 205 (Columbian Furnace Black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B (Mitsubishi Chemical Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, LI Examples of suitable black blacks include TX-50, LITX-200 (manufactured by Cabot Corporation, furnace black), Ensaco250G, Ensaco260G, Ensaco350G, and Super-P (manufactured by TIMCAL), Ketjenblack EC-300J and EC-600JD (manufactured by AkzoNobel), Denkablack, Denkablack HS-100, and FX-35 (manufactured by Denka Co., Ltd., acetylene black).

[0050] Examples of graphite include artificial graphite and natural graphite (e.g., flake graphite, lump graphite, and amorphous graphite).

[0051] The content of the conductive additive in the positive electrode mixture layer is, for example, 1 to 10 mass %, preferably 1 to 5 mass %, relative to the total mass of the positive electrode mixture layer, in order to enhance the effect of the conductive additive.

[0052] [Positive electrode current collector] The positive electrode current collector is not particularly limited, and any known positive electrode current collector can be used. Examples of materials for the positive electrode current collector include metal materials such as aluminum, aluminum alloys, stainless steel, nickel, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. Among these, aluminum is preferred as the material for the positive electrode current collector from the viewpoint of the balance between high conductivity and cost, etc. Here, "aluminum" means pure aluminum or an aluminum alloy. The positive electrode current collector is preferably made of aluminum foil, and the material of the aluminum foil is not particularly limited, but examples thereof include A1085 material and A3003 material.

[0053] [Additives] The positive electrode (positive electrode mixture layer when the positive electrode comprises a positive electrode current collector and a positive electrode mixture layer) may further contain additives other than the binder, the conductive additive, and the positive electrode active material. Examples of such additives include thickeners, surfactants, dispersants, wetting agents, antifoaming agents, and resistance reducing agents. The additives may be used singly or in combination of two or more kinds.

[0054] <Negative electrode> The negative electrode is preferably an electrode capable of absorbing and releasing lithium ions, and preferably includes the present binder and a negative electrode active material, and more preferably includes a negative electrode current collector and a negative electrode mixture layer containing the present binder and the negative electrode active material. In this case, the negative electrode mixture layer is provided on at least a portion of the surface of the negative electrode current collector.

[0055] The content of the binder in the negative electrode mixture layer is preferably 0.1 to 10 mass %, and more preferably 0.1 to 4 mass %, relative to the total mass of the negative electrode mixture layer, from the viewpoint of achieving both the physical properties (e.g., electrolyte permeability, peel strength) of the negative electrode mixture layer and the battery performance. When the content of the present binder is 0.1 mass% or more, the adhesion of the negative electrode mixture layer to the negative electrode current collector and the binding of the negative electrode active materials to each other are further improved. When the content of the present binder is equal to or less than the upper limit, the amount of the negative electrode active material in the negative electrode mixture layer can be increased, and by using the negative electrode mixture layer, a battery with a large capacity can be easily obtained.

[0056] The thickness of the negative electrode mixture layer is not particularly limited and may be the same as that of a conventionally known negative electrode mixture layer, but is preferably 30 to 500 μm, more preferably 30 to 300 μm, and even more preferably 30 to 150 μm.

[0057] [Negative electrode active material] The negative electrode active material is preferably a substance capable of absorbing and releasing lithium ions, and examples thereof include at least one selected from the group consisting of metallic lithium, lithium-containing alloys, metals or alloys capable of alloying with lithium, oxides capable of being doped with and dedoped from lithium ions, transition metal nitrides capable of being doped with and dedoped from lithium ions, and carbon materials capable of being doped with and dedoped from lithium ions. Among these, carbon materials that can be doped and dedoped with lithium ions are preferred. The negative electrode active material may be used alone or in combination of two or more.

[0058] Examples of the carbon material include carbon black, activated carbon, graphite materials (eg, artificial graphite, natural graphite), and amorphous carbon materials. The carbon material may be in any shape such as fiber, sphere, potato, or flake. The size of the carbon material is not particularly limited, but is preferably 5 to 50 μm, and more preferably 20 to 30 μm.

[0059] Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or less, and mesophase pitch carbon fiber (MCF).

[0060] Examples of graphite materials include natural graphite and artificial graphite, such as graphitized MCMB and graphitized MCF. The graphite material may contain boron. The graphite material may be coated with a metal such as gold, platinum, silver, copper, or tin, or with amorphous carbon, or may be a mixture of amorphous carbon and graphite.

[0061] [Conductive additive] The negative electrode (negative electrode mixture layer when the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer) may further contain a conductive additive other than the present binder and the negative electrode active material. The conductive additive is not particularly limited as long as it is a material other than the active material, and a known conductive additive can be used. Specific examples of the conductive additive are the same as the conductive additive contained in the positive electrode described above, and preferred examples are also the same. The content of the conductive additive in the negative electrode mixture layer is, for example, 0 to 10 mass%, preferably 0 to 5 mass%, and more preferably 0 to 3 mass%, relative to the total mass of the negative electrode mixture layer, in order to enhance the effect of the conductive additive.

[0062] [Negative electrode current collector] The negative electrode current collector is not particularly limited, and any known negative electrode current collector can be used. Examples of the material for the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is preferred as the material for the negative electrode current collector from the viewpoint of workability, and copper foil is preferred as the negative electrode current collector.

[0063] [Additives] The negative electrode (negative electrode mixture layer when the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer) may further contain additives other than the present binder, the conductive additive, and the negative electrode active material. Examples of such additives include thickeners, surfactants, dispersants, wetting agents, antifoaming agents, and resistance reducing agents. The additives may be used singly or in combination of two or more kinds.

[0064] <Electrode manufacturing method> From the viewpoint of improving the charge / discharge capacity of the resulting battery, it is preferable that at least one of the positive electrode and the negative electrode is an electrode obtained by a dry method, and it is preferable that the electrode is an electrode produced by an electrode production method including the following steps 1 and 2. Specific examples of electrodes obtained by the dry method include: Step 1: dry-mixing the binder and the active material to obtain an electrode composite material; Step 2 of producing an electrode comprising the electrode composite material and a current collector; An electrode obtained by a method for producing an electrode comprising the steps of:

[0065] <Process 1> Step 1 is a step of dry-mixing the present binder and the active material without using a solvent. In step 1, the conductive aid and / or additive may also be used. In step 1, the raw material components are preferably dry-mixed in amounts such that the content of each component in the resulting electrode composite material is in the same range as the content of each component in the electrode mixture layer.

[0066] When the conductive aid and / or additive is used, there are no particular limitations on the order in which the binder, the active material, and the conductive aid and / or additive are mixed. After the binder and the active material are mixed, the conductive aid and / or additive may be further mixed, or the binder, the active material, and the conductive aid and / or additive may be added and mixed simultaneously.

[0067] The method for dry mixing is not particularly limited, and various known methods can be used, for example, methods of mixing using a defoaming kneader, a dry ball mill, a dry bead mill, a blade planetary motion mixer, a container rotation planetary motion mixer, a crusher, a mortar, a homogenizer, a low-frequency co-oscillating acoustic mixer, a jet mill, a tumbler mixer, a miller, a Henschel mixer, or the like. Furthermore, when dry mixing, the binder may be heat-treated, for example, to soften it. The heat treatment is preferably carried out at a temperature below which the active material and the like do not decompose.

[0068] <Process 2> Step 2 is a step of producing an electrode including the electrode composite material and a current collector. Specific examples include a step of molding the electrode composite material under pressure and bonding the resulting electrode composite material to a current collector to produce an electrode, or a step of molding the electrode composite material and a current collector simultaneously under pressure and bonding the electrode composite material to a current collector to produce an electrode. A suitable example of a method for molding the electrode composite material by applying pressure is press molding. As the binding method, it is preferable to press the electrode composite material onto the current collector. After the electrode composite material is molded or pressed onto the current collector, it may be further heated and dried.

[0069] As a pressing method for the press molding or when pressing the electrode composite material onto the current collector, various known pressing methods such as roll pressing and plate pressing can be appropriately adopted. The pressure during the pressing is preferably 0.1 tons to 100 tons, more preferably 1 tons to 50 tons. There are no particular restrictions on the pressing time, but it is, for example, 0.5 seconds to 1 hour.

[0070] The pressed density of the electrode when the electrode composite material is compressed under the pressure in the above range is preferably 1.0 to 4.0 g / cm. 3 is. The press density of the positive electrode is more preferably 2.5 to 4.0 g / cm 3 is. The press density of the negative electrode is more preferably 1.0 to 2.0 g / cm 3 and more preferably 1.3 to 1.8 g / cm 3 is.

[0071] The temperature during the pressing is preferably 20 to 300°C, more preferably 80 to 200°C, and even more preferably 100 to 200°C. By forming the electrode composite material or bonding the electrode composite material to the current collector within this temperature range, the binder is appropriately softened, making it possible to effectively bond the binder to the active material and the electrode composite material to the current collector.

[0072] Examples of the heat drying method include drying with warm air, hot air, or low humidity air; vacuum drying; and drying by irradiation with infrared rays (for example, far infrared rays). The drying time and drying temperature are not particularly limited, but the drying time is, for example, 1 minute to 24 hours, and the drying temperature is, for example, 80° C. to 180° C. The heat drying may be performed as needed, but is preferably omitted from the viewpoints of simplification of electrode production, economy, safety, environmental impact, etc.

[0073] The current collector to be used may be previously subjected to surface treatment such as surface roughening or formation of a conductive adhesive layer in order to enhance adhesion to the electrode composite material.

[0074] The method for producing an electrode may further include other steps in addition to the steps 1 and 2. Examples of such other steps include a step of preparing the present binder.

[0075] <Lithium-ion secondary battery> A lithium ion secondary battery according to one embodiment of the present invention preferably includes the electrodes and an electrolyte, and may have a separator between the negative electrode and the positive electrode, and may have a case that houses the electrodes, the electrolyte, and the like. The lithium ion secondary battery includes an electrode containing the binder, and therefore has excellent charge / discharge capacity.

[0076] <Electrode> In view of the ease with which a battery having excellent battery characteristics can be obtained, it is preferable that at least one of the positive electrode and the negative electrode of the lithium ion secondary battery is an electrode obtained by a dry method, particularly an electrode manufactured by the method described in the section on the electrode manufacturing method. One of the positive electrode and the negative electrode of the lithium ion secondary battery may be an electrode manufactured by a wet method or the like.

[0077] <Electrolytes> The lithium ion secondary battery preferably contains an electrolyte. The electrolyte is not particularly limited as long as it can be a conductor of alkali metal cations such as lithium ions. The state of the electrolyte is not particularly limited, and may be, for example, a liquid dissolved in a non-aqueous solvent described below, a gel, or a solid. One type of electrolyte may be used, or two or more types may be used.

[0078] The electrolyte preferably contains at least one type of lithium salt containing fluorine (hereinafter also referred to as "fluorine-containing lithium salt"). Examples of fluorine-containing lithium salts include inorganic acid anion salts such as lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenate (LiAsF), and lithium hexafluorotantalate (LiTaF); and organic acid anion salts such as lithium trifluoromethanesulfonate (LiCFSO), lithium bis(trifluoromethanesulfonyl)imide (Li(CFSO)N), and lithium bis(pentafluoroethanesulfonyl)imide (Li(CFSO)N). Among these, LiPF is particularly preferred as the fluorine-containing lithium salt.

[0079] The lithium ion secondary battery may contain an electrolyte that is a fluorine-free lithium salt. Examples of fluorine-free lithium salts include lithium perchlorate (LiClO), lithium tetrachloroaluminate (LiAlCl), and lithium decachlorodecaborate (LiB). 10 Cl 10 ) etc.

[0080] [Electrolyte] The lithium ion secondary battery may contain an electrolytic solution in which one or more of the above electrolytes are dissolved in one or more solvents. The electrolytic solution is more preferably a non-aqueous electrolytic solution containing one or more of the above electrolytes and one or more non-aqueous solvents. The electrolytic solution may contain, in addition to the electrolyte and electrolytic solution, a conventionally known additive used for improving battery performance or the like.

[0081] The proportion of the fluorine-containing lithium salt relative to 100% by mass of the electrolyte in the electrolytic solution is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 80 to 100% by mass. The proportion of LiPF6 relative to 100% by mass of the electrolyte in the electrolytic solution is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 80 to 100% by mass.

[0082] The concentration of the electrolyte in the electrolytic solution is preferably 0.1 to 3 mol / L, more preferably 0.5 to 2 mol / L. The concentration of LiPF6 in the electrolytic solution is preferably 0.1 to 3 mol / L, and more preferably 0.5 to 2 mol / L.

[0083] The electrolytic solution preferably contains at least one non-aqueous solvent. Examples of non-aqueous solvents include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphate.

[0084] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0085] An example of the fluorine-containing cyclic carbonates is fluoroethylene carbonate (FEC).

[0086] Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC).

[0087] An example of the fluorine-containing chain carbonates is methyl 2,2,2-trifluoroethyl carbonate.

[0088] Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate.

[0089] Examples of γ-lactones include γ-butyrolactone and γ-valerolactone.

[0090] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane.

[0091] Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane.

[0092] Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile.

[0093] An example of the amides is N,N-dimethylformamide.

[0094] Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0095] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of the cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates and fluorine-containing chain carbonates in the non-aqueous solvent is preferably 50 to 100 mass%, more preferably 60 to 100 mass%, and even more preferably 80 to 100 mass%.

[0096] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total proportion of the cyclic carbonates and chain carbonates in the non-aqueous solvent is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 80 to 100% by mass.

[0097] The proportion of the non-aqueous solvent in the non-aqueous electrolyte is preferably 60 mass % or more, and more preferably 70 mass % or more. The upper limit of the proportion of the non-aqueous solvent in the non-aqueous electrolyte solution varies depending on the contents of other components, but is, for example, 99 mass %, preferably 97 mass %, and more preferably 90 mass %.

[0098] The intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25° C., from the viewpoint of further improving the dissociation property of the electrolyte and the mobility of ions.

[0099] <Separator> The separator is not particularly limited as long as it electrically insulates the positive electrode from the negative electrode and is permeable to lithium ions. Examples of materials for the separator include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc. Examples of the separator include a porous flat plate containing the resin, a nonwoven fabric containing the resin, etc. Among these, the separator is preferably a porous resin film having a single layer or multilayer structure mainly composed of one or more polyolefin resins. The thickness of the separator is, for example, 5 to 30 μm.

[0100] <Case> The case is not particularly limited, and examples thereof include known cases for lithium ion secondary batteries, and specific examples thereof include a case including a laminate film and a case including a battery can and a battery can lid.

[0101] <Method of manufacturing lithium-ion secondary batteries> Examples of methods for manufacturing lithium ion secondary batteries include known methods for manufacturing lithium ion secondary batteries, such as a manufacturing method including a precursor manufacturing step of housing a positive electrode, a negative electrode, an electrolyte (or electrolytic solution), and, if necessary, a separator in a case to manufacture a lithium ion secondary battery precursor, and an aging step of subjecting the lithium ion secondary battery precursor to an aging treatment to obtain a lithium ion secondary battery.

[0102] The case, positive electrode, negative electrode, electrolyte, separator, and electrolytic solution in the method for producing a lithium ion secondary battery are synonymous with the case, positive electrode, negative electrode, electrolyte, separator, and electrolytic solution in the lithium ion secondary battery described above, and preferred embodiments are also the same.

[0103] The precursor preparation step preferably includes a step of accommodating a positive electrode and a negative electrode (with a separator interposed therebetween as necessary) in a case, and a step of injecting an electrolyte (or an electrolytic solution) into the case accommodating the positive electrode and the negative electrode (with a separator as necessary).

[0104] In the aging step, the lithium ion secondary battery precursor is preferably subjected to a combination of charging and discharging at least once in an environment of 25 to 70°C. By including such an aging step, it is likely that the reduction in internal resistance (particularly the reduction in positive electrode resistance) of the lithium ion secondary battery can be reduced. [Example]

[0105] Hereinafter, one embodiment of the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The methods for measuring various physical properties are as follows.

[0106] <Intrinsic viscosity [η]> The intrinsic viscosity [η] of the particles was measured at 135°C by dissolving the particles in decalin.

[0107] <Average particle diameter d50> The average particle diameter d50 was determined by measuring the mass-based particle size distribution by the Coulter counter method using a precision particle size distribution analyzer (manufactured by Beckman, product name: Multisizer Three), and the particle diameter at which the cumulative mass in the mass-based particle size distribution reached 50% was defined as the average particle diameter d50.

[0108] <45μm mesh sieve penetration rate> The 45 μm mesh sieve passing rate (the proportion of particles passing through a 45 μm mesh sieve) was determined by measuring the mass of particles that passed through a 45 μm mesh sieve (JIS Z8801-1 (2019)).

[0109] <Electrode binder 1 (used in Examples 1, 4, and 6)> As the electrode binder, ultra-high molecular weight ethylene polymer fine particles (Mitsui Chemicals, Inc., Mipelon (registered trademark) PM-200, intrinsic viscosity [η] = 13.0 dl / g, MFR (190°C, 21.6 kg load) = 0.020 g / 10 min, average particle diameter d50 = 10.5 μm, 45 μm mesh sieve passing rate = 100% by mass) were used.

[0110] <Electrode binder 2 (used in Examples 2 and 5)> As the electrode binder, ultra-high molecular weight ethylene polymer fine particles (Mitsui Chemicals, Inc., Mipelon (registered trademark) XM-220, intrinsic viscosity [η] = 14.5 dl / g, MFR (190°C, 21.6 kg load) = 0.015 g / 10 min, average particle diameter d50 = 32 μm, 45 μm mesh sieve passing rate = 90% by mass) were used.

[0111] <Electrode binder 3 (used in Example 3)> As the electrode binder used in Example 3, ultra-high molecular weight ethylene polymer fine particles were prepared by the following method.

[0112] (i) Preparation of magnesium-containing carrier component (α-1) Decane was added to 95.2 g (1.0 mol) of anhydrous magnesium chloride and 390.6 g (3.0 mol) of 2-ethylhexyl alcohol to make a total volume of 1000 mL, and the reaction was carried out at 130° C. for 2 hours to obtain a homogeneous solution. Next, 100 mL of the homogeneous solution (100 mmol in terms of magnesium atoms), 50 mL of purified decane, and 560 mL of chlorobenzene were placed in a 1000 mL flask thoroughly purged with nitrogen. Using a Clearmix CLM-0.8S (M-Technique Co., Ltd.) stirring system at 15,000 rpm, 110 mmol of triethylaluminum diluted with purified decane was added dropwise over 30 minutes while maintaining the liquid temperature at 0°C. The liquid temperature was then raised to 80°C over 4 hours and allowed to react for 1 hour. Next, while maintaining the temperature at 80°C, 202 mmol of triethylaluminum diluted with purified decane was added dropwise over 30 minutes, and the reaction was continued for another 1 hour. After the reaction was complete, the solid was collected by filtration, thoroughly washed with toluene, and 100 mL of toluene was added to obtain a toluene slurry of the magnesium-containing support component (α-1).

[0113] (ii) Preparation of solid catalyst component (β-1) A 1000 mL flask thoroughly purged with nitrogen was charged with 20 mmol of the toluene slurry of the magnesium-containing carrier component (α-1) calculated as the number of magnesium atoms and 600 mL of purified toluene, and while stirring and maintaining the temperature at room temperature, 38.9 mL of a toluene solution (0.0001 mmol / mL) of a transition metal compound represented by the following formula (I) was added dropwise over 20 minutes. After stirring for 1 hour, the solid portion was collected by filtration, thoroughly washed with toluene, and purified decane was added to prepare 200 mL of decane slurry of the solid catalyst component (β-1).

[0114] [ka]

[0115] (iii) Preparation of ultra-high molecular weight ethylene polymer microparticles A 1-L stainless steel autoclave with a thoroughly nitrogen-purged interior was charged with 500 mL of purified heptane, and ethylene was passed through at room temperature at 100 L / hr for 15 minutes to saturate the liquid and gas phases. The temperature was then raised to 65°C, and 1.25 mL of a decane solution of triethylaluminum (1.0 mmol / mL in terms of aluminum atom) and 200 mL of a decane slurry of the solid catalyst component (β-1) (0.00008 mmol in terms of zirconium atom) were added while ethylene was flowing through at 12 L / hr. The mixture was stirred for 3 minutes while maintaining the temperature. 40 mg of Emulgen 108 (Kao Corporation) was added, and the ethylene pressure was immediately increased. The ethylene pressure was increased to 0.8 MPa·G over 10 minutes, and polymerization was carried out at 70°C for 2 hours while ethylene was supplied to maintain the pressure. The autoclave was then cooled, and the ethylene pressure was released. The resulting polymer slurry was filtered, washed with hexane, and dried under reduced pressure at 80° C. for 10 hours to obtain 40.9 g of ultra-high molecular weight ethylene polymer fine particles. The resulting ultra-high molecular weight ethylene polymer microparticles had an intrinsic viscosity [η] of 23.0 dl / g, an average particle size d50 of 10.7 μm, and a 45 μm mesh sieve passing rate of 99 mass %.

[0116] <Electrode binder 4 (used in Comparative Example 1)> Intrinsic viscosity [η] = 1.3 dl / g, average particle diameter d50 = 25 μm, passage rate through 45 μm mesh sieve = 92 mass %of High density polyethylene (HDPE) was used.

[0117] <Electrode Binder 5 (used in Comparative Example 2)> Ultra-high molecular weight polyethylene (PE) with an intrinsic viscosity [η] of 14.0 dl / g and an average particle size d50 of 110 μm was used.

[0118] <Preparation of electrodes by dry mixing> - Preparation of Positive Electrode (Examples 1 to 3 and Comparative Examples 1 and 2) - The positive electrode active material was NCM523 (manufactured by Umicore, composition formula LiNi 0.5 Co 0.2 Mn 0.3 O2) 920 g, and Super-P (TIMCAL, conductive carbon black, BET specific surface area: 62 m) as a conductive additive. 2 A positive electrode composite material (electrode composite material) was produced by dry-mixing 20 g of KS-6 (flake graphite, manufactured by TIMREX Corporation) and 12 g of either electrode binders 1 to 3 or electrode binders 4 to 5 using a defoaming kneader (non-bubbling kneader NBK-1, manufactured by Nippon Seiki Seisakusho Co., Ltd.) at a rotation speed of 95 rpm. The positive electrode composite material obtained above was evenly distributed on both main surfaces of an aluminum foil (thickness 20 μm, width 80 mm) serving as a current collector, and the gap between the upper and lower rolls was adjusted. Using a 1-ton roll press, the positive electrode was pressed until the press density on each side was 3.1±0.1 g / cm. 3 Then, the sheet was dried and baked in a vacuum drying oven at 150°C for 1 hour. The double-sided coated aluminum foil obtained above after drying was slit to obtain electrodes with a coated portion (front surface: 56 mm x 334 mm, back surface: 56 mm x 408 mm) and a tab welding margin, to obtain a positive electrode.

[0119] - Preparation of negative electrode (Examples 4 and 5) - A negative electrode composite material was prepared by dry-mixing 960 g of natural graphite as the negative electrode active material, 10 g of Super-P (conductive carbon black) as a conductive additive, and 22.5 g of either electrode binder 1 or 2 using a defoaming kneader (Non-bubbling kneader NBK-1 manufactured by Nippon Seiki Seisakusho Co., Ltd.) at a rotation speed of 95 rpm. The negative electrode composite material obtained above was evenly distributed on both main surfaces of the copper foil current collector, and the gap between the upper and lower rolls was adjusted. Using a 1-ton roll press, the negative electrode was pressed until the press density on one side was 1.45±0.05 g / cm. 3 Then, the sheet was dried and baked in a vacuum drying oven at 150°C for 1 hour. The double-sided coated copper foil obtained above after drying was slit to obtain an electrode having a coated portion (front surface: 56 mm x 334 mm, back surface: 56 mm x 408 mm) and a tab welding margin, thereby obtaining a negative electrode.

[0120] <Electrode fabrication by wet mixing> - Preparation of Positive Electrode (Examples 4 and 5) - 1. Slurry Preparation The positive electrode active material was NCM523 (manufactured by Umicore, composition formula LiNi 0.5 Co 0.2 Mn 0.3 920 g of O2) was mixed with 20 g of Super-P (conductive carbon black) and 20 g of KS-6 (flake graphite) as conductive additives using a 5 L planetary disperser for 10 minutes, after which 100 g of N-methylpyrrolidone (NMP) was added and mixed for an additional 20 minutes. Next, 150 g of an 8% by mass polyvinylidene fluoride (PVDF) solution (manufactured by Kureha Corporation, PVDF W#7200 dissolved in NMP; hereinafter also referred to as "8%-PVDF solution") was added and kneaded for 30 minutes, after which another 150 g of the 8%-PVDF solution was added and kneaded for 30 minutes. 200 g of the 8%-PVDF solution was then added and kneaded for 30 minutes. 80 g of the 8%-PVDF solution was then added and kneaded for 30 minutes. 27 g of NMP was then added to adjust the viscosity, and the mixture was mixed for 30 minutes, followed by vacuum degassing for 30 minutes to prepare a slurry with a solids concentration of 60% by mass.

[0121] 2. Coating and drying The applied mass after drying is 19.0 mg / cm 2 The slurry was applied to one of the main surfaces of an aluminum foil (thickness 20 μm, width 200 mm) using a die coater and dried. Next, the opposite main surface (uncoated surface) of the aluminum foil was similarly coated with a coating mass of 19.0 mg / cm 2 The slurry was applied using a die coater so that the thickness became 1 / 3 of the above, and then dried. The obtained double-sided coated aluminum foil (the total coating amount on both sides was 38.0 mg / cm 2 ) was dried in a vacuum drying oven at 130°C for 12 hours.

[0122] 3. Press Using a 1-ton roll press, the gap between the upper and lower rolls was adjusted, and the dried double-sided coated aluminum foil obtained above was pressed to a pressure of 2.9±0.05 g / cm on one side. 3 It was pressed to be.

[0123] 4. Slit The double-sided coated aluminum foil after pressing was slit to form electrodes having a coated portion (front surface: 56 mm x 334 mm, back surface: 56 mm x 408 mm) and a tab welding margin, to obtain a positive electrode.

[0124] - Preparation of Negative Electrode (Examples 1 to 3 and Comparative Examples 1 and 2) - 1. Slurry Preparation 960 g of natural graphite (as the negative electrode active material) and 10 g of Super-P (conductive carbon black) (as the conductive additive) were mixed for 5 minutes using a 5-liter planetary mixer. Then, 450 g of 1% by weight carboxymethylcellulose (CMC) (CMC dissolved in pure water, hereinafter also referred to as "1%-CMC aqueous solution") was added and mixed for an additional 30 minutes. Next, 300 g of 1%-CMC aqueous solution was added and mixed for 30 minutes, after which 250 g of 1%-CMC was added and mixed for 30 minutes. Next, 25 g of styrene-butadiene rubber (SBR) (40% by weight emulsification solvent) was added as the binder and mixed for 30 minutes. The mixture was then vacuum degassed for 30 minutes to prepare a slurry with a solids concentration of 45% by weight.

[0125] 2. Coating and drying The applied mass after drying is 11.0 mg / cm 2 The slurry was applied to one of the main surfaces of a copper foil (thickness: 10 μm) serving as a current collector using a die coater and dried, and then similarly applied to the opposite main surface (uncoated surface) of the copper foil so that the coating mass was 11.0 mg / cm. 2 The slurry was applied using a die coater so that the thickness became 1 / 3 of the above, and then dried. The obtained double-sided coated copper foil (coating amount on both sides total 22.0 mg / cm 2 ) was dried in a vacuum drying oven at 120°C for 12 hours.

[0126] 3. Press Using a 1-ton roll press, the gap between the upper and lower rolls was adjusted, and the dried double-sided coated copper foil obtained above was pressed to a density of 1.45±0.05 g / cm on one side. 3 It was pressed to be.

[0127] 4. Slit The double-sided coated copper foil after pressing was slit to obtain an electrode having a coated portion (front surface: 58 mm x 372 mm, back surface: 58 mm x 431 mm) and a tab welding margin, thereby obtaining a negative electrode.

[0128] <Battery manufacturing> Using the electrodes prepared above, batteries were prepared according to the following procedure.

[0129] First, an aluminum tab was bonded to the tab welding margin of the positive electrode using an ultrasonic bonding machine, and then a nickel tab was bonded to the tab welding margin of the negative electrode using an ultrasonic bonding machine. A polyethylene porous film (183 mm x 100 mm) with a porosity of 45% and a thickness of 25 μm was used as the separator.

[0130] 1. Lamination The negative electrode, separator, positive electrode, separator, and negative electrode were alternately stacked in this order to obtain a laminate including a total of five positive electrode layers and six negative electrode layers, with the tabs of the positive and negative electrodes on the same side. The resulting laminate was then sandwiched between laminate sheets, and three sides of the laminate sheets were heat-sealed to prepare a case containing electrodes. Note that the three sides other than the tab sides were heat-sealed so that the tabs of the positive and negative electrodes protruded from the laminate sheets.

[0131] 2. Electrolyte injection Before injecting the electrolyte, the electrode-containing case was dried under reduced pressure for 12 hours at 70° C. in a vacuum dryer. Next, 19.6±0.3 g of electrolyte (1 mol / L-LiPF6, solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), containing vinylene carbonate (VC) as an additive so that the content of the final electrolyte was 1.0 mass % with respect to the final electrolyte) was injected into the dried electrode-containing case, and then the remaining side of the electrode-containing case was heat-sealed while drawing a vacuum so that the positive and negative electrode tabs protruded from the laminate sheet.

[0132] 3. Activation (aging) treatment The case containing the electrodes, sealed on all four sides, was charged to 2.5 to 4.2 V at room temperature, held for 0.5 to 12 hours, charged to 4.2 V, and discharged to 2.8 V, in this order, multiple times. The battery was then stored at 25°C for 5 days in a fully charged state of 4.2 V (SOC 100%) to produce a stacked battery (design capacity 5 Ah).

[0133] <Charge and discharge capacity measurements> The fabricated battery (after activation treatment) was charged to a constant voltage of 4.2 V at room temperature, and the charge capacity was measured. Then, it was discharged to 2.8 V at a constant current of 0.1 C at room temperature, and the discharge capacity was measured. The results are shown in Table 1.

[0134] [Table 1]

[0135] In Table 1, the intrinsic viscosity [η] and average particle size refer to the intrinsic viscosity [η] and average particle size d50 of the electrode binder used in the dry method. In Table 1, "-" indicates that there is no measured value for the corresponding item.

[0136] By using this binder, electrodes can be produced by a dry method, and it can be seen that the (lithium ion secondary) batteries of Examples 1 to 5 have improved charge / discharge capacities compared to the (lithium ion secondary) batteries of Comparative Examples 1 and 2.

[0137] <Electrode Binder 6 (used in Examples 7 to 9)> As the electrode binder used in Examples 7 to 9, ultra-high molecular weight ethylene polymer fine particles were prepared by the following method.

[0138] (i) Preparation of magnesium-containing carrier component (α-2) A 2 L glass vessel equipped with a stirrer and thoroughly purged with nitrogen was charged with 95.2 g (1.0 mol) of anhydrous magnesium chloride, 442 mL of dehydrated decane, 260.4 g (2.0 mol) of 2-ethylhexyl alcohol, and 298.5 g (1.0 mol) of 2-octyldodecyl alcohol, and the mixture was reacted at 155°C for 4 hours to obtain a homogeneous, transparent solution. Next, 100 mmol of the homogeneous, clear solution (calculated as magnesium atoms) and 610 mL of dehydrated decane were placed in a separate 1 L glass vessel equipped with a stirrer and thoroughly purged with nitrogen. Using a homogenizer (Clearmix CLM-1.5S, M-Technique Co., Ltd.), 109 mmol of triethylaluminum was slowly added dropwise while maintaining the liquid temperature at 0°C under vigorous stirring at 18,000 rpm. The liquid temperature was then raised to 80°C over 4 hours, and 188 mmol of triethylaluminum was added dropwise again while maintaining the temperature at 80°C. The reaction was continued for another hour. After completion of the reaction, the solid was collected by filtration, thoroughly washed with dehydrated xylene, and 200 mL of dehydrated xylene was added to prepare a xylene slurry of magnesium-containing support component (α-2). The magnesium concentration of the prepared magnesium-containing support component (α-2) was 0.21 mmol / mL and the aluminum concentration was 0.022 mmol / mL.

[0139] (ii) Preparation of solid catalyst component (β-2) A 200 mL glass reactor thoroughly purged with nitrogen was charged with 56.1 mL of xylene and, with stirring, 28.9 mL of the xylene slurry of the magnesium-containing support component (α-2) prepared above (5.95 mmol in terms of magnesium atoms). Next, 28.3 mg of a transition metal compound represented by the following formula (II) (0.0329 mmol in terms of zirconium atoms) was charged and reacted at room temperature for 1 hour. The reaction mixture was then filtered, and the residue was washed once with 50 mL of xylene and twice with 50 mL of decane. Next, after filtration, 105 mL of decane was added to the residue to produce a decane slurry of the solid catalyst component (β-2). A portion of the resulting decane slurry of the solid catalyst component (β-2) was sampled to examine its concentration, which revealed that the zirconium concentration was 0.000373 mmol / mL and the magnesium concentration was 0.0699 mmol / mL.

[0140] [ka]

[0141] (iii) Preparation of ultra-high molecular weight ethylene polymer microparticles A 1 L stainless steel autoclave with a thoroughly nitrogen-purged interior was charged with 500 mL of decane, and ethylene was passed through it at 0.4 NL / min for 15 minutes at room temperature to saturate the liquid and gas phases. The temperature was then raised to 65°C, and while ethylene was still flowing at 0.4 NL / min, 1.25 mL of a decane solution of triisobutylaluminum (1.0 mmol / mL in terms of aluminum atoms) and 11.4 mL of the decane slurry of the solid catalyst component (β-2) (0.80 mmol in terms of magnesium atoms) were added. The mixture was stirred for 5 minutes while maintaining the temperature. Then, 6 mL of a decane solution (15 mg / mL) of Emulgen 108 (Kao Corporation) was added, the ethylene flow was stopped, 1 mL of hydrogen was added, and the temperature was raised to 70°C. Ethylene was then added at a rate of 1.0 NL / min until the pressure reached 0.35 MPaG. After reaching 0.35 MPaG, polymerization was continued while maintaining the temperature and pressure until the ethylene feed rate reached 56 NL. The autoclave was then cooled, and the ethylene pressure was released. The resulting slurry containing white solids was filtered, and the residue was washed with heptane and dried under reduced pressure at 80°C for 10 hours, yielding 68.6 g of ultra-high molecular weight ethylene polymer microparticles. The resulting ultra-high molecular weight ethylene polymer microparticles had an intrinsic viscosity [η] of 11.9 dl / g, an average particle size d50 of 6.2 μm, and a 45 μm mesh sieve passing rate of 100 mass %.

[0142] <Electrode binder 7 (used in Example 10)> As the electrode binder used in Example 10, ultra-high molecular weight ethylene polymer fine particles were prepared by the following method.

[0143] In the same manner as in the preparation of electrode binder 6, a magnesium-containing support component (α-2) and a solid catalyst component (β-2) were prepared. In the preparation process of the ultra-high molecular weight ethylene polymer microparticles for electrode binder 6, 69.8 g of ultra-high molecular weight ethylene polymer microparticles were obtained in the same manner as for electrode binder 6, except that after the decane solution of Emulgen 108 was charged, the flow of ethylene was not stopped and 1 mL of hydrogen was not charged. The resulting ultra-high molecular weight ethylene polymer microparticles had an intrinsic viscosity [η] of 24.6 dl / g, an average particle size d50 of 6.4 μm, and a 45 μm mesh sieve passing rate of 100 mass %.

[0144] [Example 6] A negative electrode composite material was prepared by dry mixing 48 g of natural graphite as a negative electrode active material and 1:2.0 g of electrode binder using a lab mill (IFM-800 LM-PLUS manufactured by Iwatani Corporation) at a rotation speed of 20,000 rpm. The negative electrode composite material obtained above was placed in the gap between two rolls of a calendar roll molding machine set at 200°C, and the weight was measured at 1.45±0.05 g / cm 3 The gap between the rolls was adjusted so that a negative electrode mixture layer having a thickness of 135 μm was obtained.

[0145] <Tensile strength of negative electrode mixture layer> The resulting negative electrode composite layer was cut into a 5 mm wide test piece in the rolling direction of the roll. The tensile strength (at break) of the test piece in the rolling direction was measured using a tensile tester (Instron Corporation, Universal Testing Machine Model 5982) at a temperature of 23°C, a chuck distance of 10 mm, and a pulling rate of 1 mm / min.

[0146] <Electrolyte penetration> The resulting negative electrode composite layer was punched out to a diameter of 17 mm and attached to a parallel, smooth glass surface so as not to move. 0.2 mL of the same electrolyte solution as used in the production of the coin-type battery described below was dropped onto the surface of the negative electrode composite layer, and the layer was covered with a glass dish to prevent the electrolyte from drying. The time it took for the electrolyte to penetrate into the negative electrode composite layer was measured visually.

[0147] <Making a coin-type battery> An electrolyte solution (1 mol / L-LiPF6, solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), containing vinylene carbonate (VC) as an additive so that the final electrolyte solution contained 1.0 mass% of the additive) was prepared.

[0148] The above-mentioned negative electrode composite layer and copper foil having a thickness of 10 mm were stacked and punched into a disk shape with a diameter of 14 mm. Furthermore, lithium foil was punched into a disk shape with a diameter of 13 mm as a positive electrode, thereby obtaining a coin-shaped negative electrode (a laminate of the negative electrode composite layer and copper foil) and a coin-shaped positive electrode, respectively. Also, a microporous polyethylene film having a thickness of 20 μm was punched into a disk having a diameter of 17 mm to obtain a coin-shaped separator.

[0149] The obtained coin-shaped negative electrode, separator, and positive electrode were stacked in this order in a stainless steel battery can (2032 size), and then 20 μL of the electrolyte obtained above was poured into the battery can, and the electrolyte was mixed with the separator, positive electrode, and negative electrode. Soaking made him do so. Next, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery was sealed by crimping the battery can lid with a polypropylene gasket in between. As a result of the above, a coin-type battery (that is, a coin-type lithium secondary battery) having a diameter of 20 mm and a height of 3.2 mm was obtained.

[0150] The obtained coin-type batteries were charged to 2.5 to 4.2 V at room temperature, held for 0.5 to 12 hours, charged to 4.2 V, and discharged to 2.8 V, in this order, multiple times. They were then stored at 25°C for 5 days in a fully charged state of 4.2 V (SOC 100%), and subjected to an activation (aging) treatment.

[0151] <Charge and discharge capacity measurements> After activation, the coin-type battery was charged to a constant voltage of 4.2 V at room temperature, and the charge capacity (first cycle) was measured. It was then discharged to 2.8 V at a constant current of 0.1 C at room temperature, and the discharge capacity (first cycle) was measured. The results are shown in Table 2.

[0152] <Charge and discharge efficiency measurements> The same operations as those for measuring the charge capacity and discharge capacity were further repeated to measure the charge capacity (second cycle) and discharge capacity (second cycle). The ratio of the charge capacity (second cycle) to the charge capacity (first cycle) obtained above was calculated as the charge efficiency. The ratio of the discharge capacity (second cycle) to the discharge capacity (first cycle) obtained above was calculated as the discharge efficiency.

[0153] [Example 7] A battery was fabricated and evaluated in the same manner as in Example 6, except that the type of electrode binder used was changed from Electrode Binder 1 to Electrode Binder 6.

[0154] [Example 8] A battery was fabricated and evaluated in the same manner as in Example 6, except that the type of binder used was changed from Electrode Binder 1 to Electrode Binder 6 and the amount of binder used was changed from 2.0 g to 1.5 g.

[0155] [Example 9] A battery was fabricated and evaluated in the same manner as in Example 6, except that the type of binder used was changed from Electrode Binder 1 to Electrode Binder 6 and the amount of binder used was changed from 2.0 g to 1.0 g.

[0156] [Example 10] A battery was fabricated and evaluated in the same manner as in Example 6, except that the type of binder used was changed from Electrode Binder 1 to Electrode Binder 7.

[0157] [Table 2]

[0158] In Table 2, the intrinsic viscosity [η] and the average particle size refer to the intrinsic viscosity [η] and the average particle size d50 of the electrode binder used in the dry method.

[0159] By using this binder, electrodes can be produced by a dry method, and it is clear that the lithium ion secondary batteries of Examples 6 to 10 are excellent in charge / discharge capacity and charge / discharge efficiency.

Claims

1. An electrode mixture layer which is a positive electrode mixture layer or a negative electrode mixture layer, the positive electrode mixture layer contains an electrode binder, a conductive additive, and a positive electrode active material, and the content of the electrode binder in the positive electrode mixture layer is 0.1 to 4 mass% with respect to the total mass of the positive electrode mixture layer; the negative electrode mixture layer contains an electrode binder and a negative electrode active material, and the content of the electrode binder in the negative electrode mixture layer is 0.1 to 4 mass% with respect to the total mass of the negative electrode mixture layer; The electrode binder contains ultra-high molecular weight olefin polymer fine particles (A) that satisfy the following requirements (i) to (iii): Electrode mixture layer: (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 5 to 50 dl / g; (ii) the average particle diameter d50 in the mass-based particle size distribution determined by the Coulter counter method is in the range of 1 to 50 μm; (iii) 50% by mass or more passes through a 45 μm mesh sieve.

2. 2. The electrode mixture layer according to claim 1, wherein the average particle diameter d50 of the ultra-high molecular weight olefin polymer fine particles (A) is in the range of 3 to 15 μm.

3. The electrode mixture layer according to claim 1 , wherein the ultra-high molecular weight olefin polymer fine particles (A) are ethylene polymer fine particles.

4. An electrode comprising the electrode mixture layer according to any one of claims 1 to 3 and a current collector.

5. 5. The electrode according to claim 4, which is an electrode obtained by a dry process.

6. A lithium ion secondary battery comprising the electrode according to claim 4 and an electrolyte.

7. A process for obtaining an electrode composite material by dry-mixing an electrode binder containing ultra-high molecular weight olefin polymer fine particles (A) that satisfy the following requirements (i) to (iii) and an active material; producing an electrode comprising the electrode composite and a current collector; Including, The content of the electrode binder in the electrode composite material is 0.1 to 4 mass%. Electrode manufacturing method: (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 5 to 50 dl / g; (ii) the average particle diameter d50 in the mass-based particle size distribution determined by the Coulter counter method is in the range of 1 to 50 μm; (iii) 50% by mass or more passes through a 45 μm mesh sieve.

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