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

Abstract

To provide an electrode binder that can provide an electrode that is less likely to deform due to an external force. The present invention provides an electrode binder comprising olefin polymer particles (A) that satisfy the following requirements (i) to (iii), an electrode comprising the electrode binder, a lithium ion secondary battery, and a method for producing the electrode; (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 1 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.

Description

[Technical Field]

[0001] The present invention relates to an electrode binder, an electrode, a lithium ion secondary battery, and 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, laptop computers, 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 batteries such as lithium-ion secondary batteries is a wet method in which a binder resin is dissolved or dispersed in a solvent, an active material and a conductive additive are dispersed therein to form a slurry, the slurry is applied to a current collector, and the solvent is then volatilized. Another well-known method for manufacturing electrodes is a dry method 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. As an electrode binder that can be used to prepare electrodes by a dry method and can provide batteries with excellent charge / discharge capacities, for example, Patent Document 3 discloses an electrode binder containing ultra-high molecular weight olefin polymer fine particles (A) that meet specific requirements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2019-508896 [Patent Document 2] Japanese Patent Publication No. 2020-202159 [Patent Document 3] International Publication No. 2023 / 182081 Summary of the Invention [Problem to be solved by the invention]

[0006] Although the electrode binder disclosed in Patent Document 3 can provide a battery with excellent charge / discharge capacity, further improvement is required in terms of the rigidity of the resulting electrodes.

[0007] An object of one embodiment of the present invention is to provide an electrode binder that can provide an electrode that is resistant to deformation due to an external force. Another problem to be solved by one embodiment of the present invention is to provide an electrode that is resistant to deformation due to an external force, a lithium ion secondary battery including the electrode, and a method for manufacturing the electrode. [Means for solving the problem]

[0008] The means for solving the above problems include the following aspects. <1> An electrode binder comprising olefin polymer particles (A) satisfying the following requirements (i) to (iii): (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 1 to 10 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) The amount passing through a 45 μm mesh sieve is 50% by mass or more. <2> The average particle size d50 of the olefin polymer particles (A) is in the range of 1 to 15 μm. <1> The electrode binder according to claim 1. <3> The olefin polymer particles (A) are ethylene polymer particles. <1> or <2> The electrode binder according to claim 1. <4> <1> ~ <3> 10. An electrode comprising the electrode binder according to any one of 1 to 9 and an active material. <5> The negative electrode, <4> The electrode according to claim 1. <6> The electrode is obtained by the dry method. <4> or <5> The electrode according to claim 1. <7> <4> ~ <6> 10. A lithium ion secondary battery comprising the electrode according to any one of the above items and an electrolyte. <8> <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]

[0009] According to one embodiment of the present invention, there is provided an electrode binder that can provide an electrode that is resistant to deformation due to an external force. Furthermore, according to one embodiment of the present invention, there are provided an electrode that is resistant to deformation due to an external force, a lithium ion secondary battery including the electrode, and a method for manufacturing the electrode. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] <Electrode binder> The electrode binder according to the present invention contains olefin polymer 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 1 to 10 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) The amount passing through a 45 μm mesh sieve is 50% by mass or more. The electrode binder according to the present invention has the above-mentioned structure, and thus an electrode that is resistant to deformation due to an external force can be obtained. The reason for this is not clear, but the following mechanism is presumed. It is presumed that in electrodes obtained by a dry method, the electrode binder contains olefin-based polymer particles (e.g., ethylene-based polymer particles), which improves adhesion and rigidity and suppresses a decrease in charge / discharge capacity. Electrode binders containing ultra-high molecular weight olefin polymer particles that meet specific requirements have excellent oxidation-reduction resistance. In other words, they can suppress irreversible loss of battery capacity during the electrode's oxidation-reduction process, making it easier to maintain charge-discharge efficiency. Furthermore, because the olefin polymer particles have an intrinsic viscosity [η] in the range of 1 to 10 dl / g measured in decalin at 135°C, they are presumed to melt easily at lower temperatures and possess flexibility. Therefore, electrode binders containing ultra-high molecular weight olefin polymer particles that meet specific requirements can enhance adhesion to active materials, etc., and electrodes containing such electrode binders can fully demonstrate their resistance to deformation under stress. Each component constituting the electrode binder will be described in detail below.

[0012] <<Olefin polymer particles (A)>> The olefin polymer particles (A) (hereinafter, sometimes referred to as "polymer particles (A)") satisfy the following requirements (i) to (iii). [Requirement (i)] (i): The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 1 to 10 dl / g. When the intrinsic viscosity is within the above range, the polymer particles (A) maintain their particle shape even when in a molten state, and are therefore less likely to flow out of the electrode, which is preferable because it improves the adhesion between the polymer particles (A) and the active material, etc., described below, and makes it easy to obtain a battery with excellent charge / discharge capacity and enables the preparation of an electrode by a dry method. From the above viewpoint, the intrinsic viscosity [η] of the polymer particles (A) is preferably 1.5 to 8 dl / g, more preferably 2 to 6 dl / g, and even more preferably 2 to 5 dl / g.

[0013] [Requirement (ii)] (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 makes it easy to obtain a battery with excellent charge / discharge capacity and enables the preparation of electrodes by a dry process. From this viewpoint, the upper limit of the average particle diameter d50 is preferably 15 μm, more preferably 13 μm, even more preferably 10 μm, and particularly preferably 8 μm. The lower limit of the average particle diameter d50 is preferably 2 μm, more preferably 3 μm, and even more preferably 4 μm. From the viewpoint of obtaining an electrode that is less likely to deform due to external forces, the average particle diameter d50 is preferably 1 to 15 μm, more preferably 2 to 13 μm, even more preferably 3 to 10 μm, particularly preferably 4 to 10 μm, and most preferably 4 to 8 μm. When the average particle diameter d50 is within the above range, the electrode binder can penetrate more fully between particles of the active material, etc., and the binding strength with the active material is increased even when the amount of the electrode binder is small, so that the desired effect can be achieved even when the amount of the binder used is reduced. Therefore, the amount of the active material, etc. contained in the electrode can be increased, and as a result, a battery with excellent battery performance can be easily obtained.

[0014] Furthermore, when the average particle size d50 of the polymer particles (A) is approximately the same as the particle sizes 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 size d50 of the polymer particles (A) means the average primary particle size. The method for measuring the average particle diameter d50 is not particularly limited, and it can be measured by the Coulter counter method, a laser diffraction particle size distribution analyzer, or the like. The Coulter counter method is a preferred method for measuring the average particle diameter d50. The average particle diameter d50 measured by the Coulter counter method is the value at which the integrated value of the particle size distribution is 50 mass% when measured by the mass-based particle size distribution using the Coulter counter method. Specifically, it can be determined by the measurement method described in the Examples.

[0015] [Requirement (iii)] (iii): The amount passing through a 45 μm mesh sieve is 50% by mass or more. The amount passing through a 45 μm mesh sieve means that the amount passing through a 45 μm mesh sieve (JIS Z 8801-1 2019) when a vibrating sieve or an ultrasonic vibrating sieve is used is 50 mass% or more of the total mass of the polymer particles (A). When the amount passing through a mesh sieve with 45 μm openings is 50 mass% or more of the total mass of the polymer 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.

[0016] The passing amount of 50% by mass or more means that the amount of coarse particles present in the polymer particles (A) is small. A small amount of coarse particles is considered preferable because the amount of active material and the like retained by the polymer particles (A) increases. Furthermore, a small amount 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 the above viewpoint, the amount of polymer particles (A) passing through a 45 μm mesh sieve is preferably 90 mass % or more, more preferably 95 mass % or more, and even more preferably 99 mass % or more, based on the total mass of polymer particles (A).

[0017] The polymer particles (A) are not particularly limited as long as they satisfy the requirements (i) to (iii), and examples thereof include homopolymer particles such as polyethylene, polypropylene, poly-1-butene, and poly-4-methyl-1-pentene; and copolymer particles using, as raw materials, at least two α-olefins selected from ethylene, propylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene.

[0018] The polymer particles (A) are preferably ethylene polymer particles, from the viewpoint of obtaining an electrode that is less likely to deform when subjected to an external force. When the olefin polymer particles (A) are ethylene polymer particles, the ethylene polymer particles have a lower melting point than, for example, polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), and therefore can maintain their binding strength with active materials, etc., without the need for high temperatures during electrode production. Furthermore, the ethylene polymer has a higher surface free energy than PTFE, PVDF, etc., and therefore has a higher affinity with active materials, etc., and a higher binding strength with active materials, etc. The ethylene-based polymer particles may be ethylene homopolymer particles or ethylene copolymer particles which are copolymers of ethylene and an α-olefin, and among these, ethylene homopolymer particles are preferred as the ethylene-based polymer particles.

[0019] The content of ethylene-derived structural units in the ethylene-based copolymer is preferably 50 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more, relative to a total of 100 mol of all structural units constituting the copolymer. The α-olefin in the ethylene copolymer may be one type alone or two or more types in combination.

[0020] The melt flow rate (MFR) of the polymer particles (A) is preferably 0.001 to 100 g / 10 min, more preferably 0.01 to 30 g / 10 min, and even more preferably 0.5 to 30 g / 10 min. 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.

[0021] The method for producing the polymer particles (A) is not particularly limited as long as the polymer particles (A) satisfy the above requirements (i) to (iii). For example, the polymer 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

[0022] The polymer particles (A) may be produced using only biomass-derived raw materials, only fossil fuel-derived raw materials, or both biomass-derived raw materials and fossil fuel-derived raw materials as 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 -12and 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 polymer particles (A) contain structural units derived from raw materials derived from biomass from the viewpoint of reducing the environmental load (mainly greenhouse gas emissions). Regarding the polymer particles (A), if the production conditions of the polymer particles (A), such as the polymerization catalyst, polymerization process, and polymerization temperature, are equivalent, even if the polymer particles (A) are 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.

[0023] In order to easily obtain a battery having excellent charge / discharge capacity and to easily prepare an electrode by a dry method, the lower limit of the content of the polymer particles (A) in the electrode 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. The upper limit of the content is preferably 100% by mass. The polymer particles (A) may be used in the electrode binder either singly or in combination of two or more kinds.

[0024] <<Other ingredients>> The electrode binder may further contain components other than the polymer particles (A) (hereinafter also referred to as "other components"), if necessary. Other components include conventionally known components used in electrode binders, such as olefin polymer particles other than the polymer particles (A), polyvinyl acetate, polymethyl methacrylate, carboxymethyl cellulose (CMC), nitrocellulose, rubber particles, and fluororesin.

[0025] 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.

[0026] The content of the other components in the electrode 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 polymer particles (A) in the electrode 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 electrode binder does not contain the other components mentioned above.

[0027] 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).

[0028] <Electrode> The electrode according to the present invention preferably contains the electrode binder and an active material. Since the electrode contains the electrode binder, the electrode can be produced by a dry method, and a battery that is resistant to deformation due to external forces and has 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, but is preferably a negative electrode from the viewpoint of easily obtaining an electrode that is less likely to deform when subjected to an external force.

[0029] <<Negative electrode>> The negative electrode is preferably an electrode capable of absorbing and releasing lithium ions. The negative electrode preferably includes the electrode binder and a negative electrode active material described later, and more preferably includes a negative electrode current collector described later and a negative electrode composite layer containing the electrode binder and the negative electrode active material. When the negative electrode includes the negative electrode current collector and the negative electrode composite layer, the negative electrode composite layer is preferably provided on at least a portion of the surface of the negative electrode current collector.

[0030] The content of the electrode binder in the negative electrode composite layer is preferably 0.1 to 10 mass %, more preferably 0.1 to 5 mass %, and even more preferably 1 to 4 mass %, relative to the total mass of the negative electrode composite layer, from the viewpoint of achieving both the physical properties (e.g., electrolyte permeability, peel resistance) of the negative electrode composite layer and battery performance. When the content of the electrode binder is 0.1% by 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 electrode binder is 10% by mass or less, a larger amount of the negative electrode active material can be contained in the negative electrode mixture layer. Therefore, by including the negative electrode mixture layer in the negative electrode, a battery with a large capacity can be easily obtained.

[0031] The thickness of the negative electrode mixture layer is not particularly limited and may be approximately the same as that of conventionally known negative electrode mixture layers. The thickness of the negative electrode mixture layer is preferably 30 to 500 μm, more preferably 50 to 300 μm, and even more preferably 100 to 200 μm.

[0032] [Negative electrode active material] The negative electrode active material is preferably a material capable of absorbing and releasing lithium ions, and examples of the negative electrode active material 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 doping and dedoping with lithium ions, transition metal nitrides capable of doping and dedoping with lithium ions, and carbon materials capable of doping and dedoping with lithium ions. Among these, a carbon material capable of doping and dedoping lithium ions is preferable as the negative electrode active material. The negative electrode active material may be used alone or in combination of two or more.

[0033] Examples of carbon materials that can be doped and dedoped with lithium ions include carbon black, activated carbon, graphite materials, 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 preferably 5 to 50 μm, and more preferably 20 to 30 μm.

[0034] Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch carbon fiber (MCF).

[0035] Examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include 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. Generally speaking, carbon refers to "carbon materials in general," while graphite refers to "carbon materials that have been graphitized."

[0036] [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 electrode 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 examples thereof include known conductive additives. Note that, when the carbon material is used as the negative electrode active material in the negative electrode mixture layer, a conductive additive may or may not be used. The conductive assistant is preferably a carbon material having electrical conductivity, and examples thereof include graphite, carbon black, conductive carbon fiber (for example, carbon nanotube, carbon nanofiber, carbon fiber), and fullerene. The conductive assistant may be used alone or in combination of two or more kinds.

[0037] The carbon black may be synthesized or may be a commercially available product. 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).

[0038] Examples of graphite include artificial graphite and natural graphite (e.g., flake graphite, lump graphite, and amorphous graphite).

[0039] 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.

[0040] [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, etc. Copper foil is preferred as the negative electrode current collector. The copper foil may be pure copper foil or copper alloy foil. Examples of copper foil include rolled copper foil and electrolytic copper foil. The thickness of the copper foil is not particularly limited, but may be in the range of 1 to 500 μm, for example. The negative electrode current collector may or may not have a conductive adhesive layer. When the negative electrode current collector has a conductive adhesive layer, it is preferable that the conductive adhesive layer be provided on the surface of the negative electrode current collector. When the negative electrode current collector has a conductive adhesive layer, the resulting electrode tends to have excellent resistance to peeling (e.g., adhesion) from the current collector compared to an electrode not having a conductive adhesive layer. The conductive adhesive layer may be a known conductive adhesive layer used for a negative electrode current collector.

[0041] [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 electrode 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.

[0042] <Positive electrode> The positive electrode is preferably an electrode capable of absorbing and releasing lithium ions. The positive electrode preferably includes the electrode binder, a conductive additive, and a positive electrode active material described below, and more preferably includes a positive electrode composite layer containing the electrode binder, the conductive additive, and the positive electrode active material, and a positive electrode current collector. When the positive electrode includes a positive electrode composite layer and a positive electrode current collector, the positive electrode composite layer is preferably provided on at least a portion of the surface of the positive electrode current collector.

[0043] The content of the electrode binder in the positive electrode composite layer is preferably 0.1 to 10 mass %, more preferably 0.1 to 5 mass %, and even more preferably 1 to 4 mass %, relative to the total mass of the positive electrode composite layer, from the viewpoint of achieving both the physical properties (e.g., electrolyte permeability, peeling resistance) of the positive electrode composite layer and battery performance. When the electrode binder content is 0.1% by 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 electrode binder content is 10% by mass or less, the amount of positive electrode active material in the positive electrode mixture layer can be increased. Therefore, when the positive electrode includes a positive electrode mixture layer, a battery with a large capacity can be easily obtained.

[0044] 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. The thickness of the positive electrode mixture layer is preferably 30 to 500 μm, more preferably 30 to 300 μm, and even more preferably 30 to 150 μm.

[0045] [Cathode active material] The positive electrode active material is preferably a material capable of absorbing and releasing lithium ions, and examples of the positive electrode active material include positive electrode active materials commonly used in lithium ion secondary batteries. The positive electrode active material may be used alone or in combination of two or more.

[0046] Examples of the positive electrode active material include an oxide containing lithium (Li) and nickel (Ni) as constituent metal elements; An oxide containing, as constituent metal elements, Li, Ni, and at least one metal element other than Li and Ni (e.g., transition metal elements, typical metal elements); Examples include:

[0047] 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.

[0048] The positive electrode active material preferably contains a lithium-containing composite oxide (nickel cobalt manganese oxide (NCM), 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.

[0049] LiNi a Co b Mn c O2...Formula (C1) [In formula (C1), a, b, and c each independently represent a value greater than 0 and less than 1, and the sum of a, b, and c is 0.99 to 1.00.]

[0050] 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, LiN0.8 C 0.1 Mn 0.1 O2 is one example.

[0051] The positive electrode active material may contain a lithium-containing composite oxide (nickel cobalt aluminum oxide (NCA), hereinafter also referred to as "NCA") represented by the following formula (C2).

[0052] 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.]

[0053] A specific example of NCA is LiNi 0.8 Co 0.15 Al 0.05 O2 is one example.

[0054] 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.

[0055] [Conductive additive] The conductive additive contained in the positive electrode mixture layer is not particularly limited as long as it is a material other than the positive electrode active material, and a known conductive additive can be used. Specific examples of the conductive additive are the same as those of the conductive additive in the negative electrode described above, and preferred embodiments are also the same.

[0056] 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.

[0057] [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.

[0058] [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 electrode 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.

[0059] <<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. The electrode manufacturing method is as follows: Step 1: dry-mixing an electrode 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; Preferably, the manufacturing method comprises:

[0060] <Process 1> Step 1 is a step of dry-mixing an electrode binder and the active material to obtain an electrode composite material, in which the electrode binder and the active material are dry-mixed without using a solvent or dispersion medium. 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.

[0061] When the conductive aid and / or additive is used, there is no particular limitation on the order in which the electrode binder, the active material, and the conductive aid and / or additive are mixed. After the electrode binder and the active material are mixed, the conductive aid and / or additive may be further mixed, or the electrode binder, the active material, and the conductive aid and / or additive may be added and mixed simultaneously.

[0062] 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 mill, a Henschel mixer, a Banbury mixer, a single-screw extruder, a twin-screw extruder, a calendar roll, or the like. Furthermore, when dry mixing, for example, heat treatment may be performed to soften the electrode binder. The heat treatment is preferably performed at a temperature below which the active material and the like do not decompose.

[0063] <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.

[0064] 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 to 100 tons, more preferably 1 to 50 tons, and even more preferably 1 to 15 tons. There are no particular restrictions on the pressing time, but it is, for example, 0.05 seconds to 1 hour.

[0065] 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.

[0066] 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 electrode binder is softened appropriately, making it possible to effectively bond the electrode binder to the active material and the electrode composite material to the current collector.

[0067] The method of heat drying is not particularly limited, and examples thereof 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 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.

[0068] The current collector used to prepare the electrode may be previously subjected to surface treatment such as surface roughening or the formation of a conductive adhesive layer in order to enhance adhesion to the electrode composite material.

[0069] 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 an electrode binder.

[0070] <<Lithium-ion secondary battery>> The lithium ion secondary battery according to the present invention includes the electrodes and an electrolyte. The lithium ion secondary battery 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 an electrode binder, and therefore has excellent battery characteristics (for example, the charge / discharge capacity of the battery).

[0071] <Electrode> In view of the ease of obtaining a battery with excellent battery characteristics, 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 or 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 dry method, and the other electrode may be an electrode manufactured by a wet method or the like.

[0072] <Electrolyte> 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.

[0073] 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.

[0074] 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.

[0075] [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.

[0076] 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.

[0077] 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.

[0078] The electrolyte 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.

[0079] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0080] An example of the fluorine-containing cyclic carbonates is fluoroethylene carbonate (FEC).

[0081] 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).

[0082] Examples of fluorine-containing chain carbonates include methyl 2,2,2-trifluoroethyl carbonate.

[0083] 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.

[0084] Examples of γ-lactones include γ-butyrolactone and γ-valerolactone.

[0085] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane.

[0086] Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane.

[0087] Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile.

[0088] An example of the amides is N,N-dimethylformamide.

[0089] Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0090] 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%.

[0091] 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.

[0092] 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 %.

[0093] 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.

[0094] <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.

[0095] <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.

[0096] <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.

[0097] 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.

[0098] 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).

[0099] 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]

[0100] 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.

[0101] <Intrinsic viscosity [η]> The intrinsic viscosity [η] of the olefin polymer particles (A) was measured at 135° C. by dissolving the polymer in decalin.

[0102] <Average particle diameter d50> When the average particle diameter d50 of the olefin polymer particles (A) is 100 μm or less, the mass-based particle size distribution is measured using a particle size distribution analyzer (Coulter Counter Multisizer 4e, manufactured by Beckman Coulter, Inc.), and the particle diameter at which the cumulative mass value in the mass-based particle size distribution is 50% is defined as the average particle diameter d50. When the average particle diameter d50 of the olefin polymer exceeded 100 μm, sieves with different mesh sizes were used, and the mass of the particles (unpassed particles) remaining on each sieve was calculated. From the calculated data, a cumulative distribution (cumulative unpassed particles (%) / sieve mesh size (μm)) was plotted, and the mesh size of the sieve at which the unpassed particles accounted for 50 mass% was determined as the average particle diameter d50 of the particles.

[0103] <Amount passing through a 45 μm mesh sieve> The amount passing through a 45 μm mesh sieve (the proportion of particles passing through a 45 μm mesh sieve) was measured by measuring the mass of particles passing through a 45 μm mesh sieve (JIS Z 8801-1 2019).

[0104] "Raw materials" <Polymer particles (A)> ·Polymer particles (A-1) Polymer particles were used that were produced in the same synthesis method as in the synthesis method for fine particles (B-3) described in paragraph

[0083] of JP 2022-151508 A, except that the amounts of catalyst and hydrogen used were adjusted to have the following physical properties. Intrinsic viscosity [η]=4.7dl / g MFR (190°C, 21.6 kg load) = 0.70 g / 10 min Average particle diameter d50=6.2μm 45 μm mesh sieve passing rate = 100% by mass

[0105] <Polymer particles (C)> ·Polymer particles (C-1) Ultra-high molecular weight ethylene polymer particles (Mitsui Chemicals, Inc., Million (registered trademark) 030S) were used. Intrinsic viscosity [η]=5.0dl / g MFR (190°C, 21.6 kg load) = 0.50 g / 10 min Average particle diameter d50=130μm 45μm mesh sieve passing rate: Less than 50% by mass

[0106] ·Polymer particles (C-2) Ultra-high molecular weight ethylene polymer fine particles (Mipelon (registered trademark) PM-200, manufactured by Mitsui Chemicals, Inc.) were used. Intrinsic viscosity [η]=13.0dl / g MFR (190°C, 21.6 kg load) = 0.020 g / 10 min Average particle diameter d50=12.0μm 45 μm mesh sieve passing rate = 100% by mass

[0107] ·Polymer particles (C-3) Polymer particles were produced using the same method as the synthesis method for fine particles (B-3) described in paragraph

[0083] of JP-A No. 2022-151508, and the obtained polymer particles were used. Intrinsic viscosity [η]=10.8dl / g MFR (190°C, 21.6 kg load) = 0.030 g / 10 min Average particle diameter d50=6.2μm 45 μm mesh sieve passing rate = 100% by mass

[0108] [Example 1] [Preparation of negative electrode] As an electrode binder, 3 parts by mass of polymer particles (A-1) and 97 parts by mass of natural graphite particles were mixed three times for 30 seconds at 23°C using a lab mill (manufactured by Iwatani Corporation, IFM-800, LM-PLUS) to obtain composite particles for the negative electrode. Next, the composite particles for a negative electrode were fed to the rolls of a calendar roll press machine (roll temperature: 180° C., roll press linear pressure: 0.5 T / cm) using a quantitative feeder. Next, the electrolytic copper foil (negative electrode current collector) on which the conductive adhesive layer was formed was inserted between the calendar roll presses, and the composite particles for the negative electrode supplied from the quantitative feeder were attached to the surface of the copper foil on which the conductive adhesive layer was formed, followed by pressure molding at a molding speed of 1.0 m / min to form a composite with a thickness of 125 μm and a density of 1.54 g / cm. 3 , basis weight 19.5mg / cm 2 An electrode was fabricated in which an electrode mixture layer was formed on one surface of a copper foil current collector.

[0109] <Thickness of negative electrode composite layer> The thickness of the negative electrode composite layer was measured at three points in the electrode obtained above using a film thickness meter (manufactured by NIKON Corporation, model number: DIGIMICRO MH-15M). The thickness of the negative electrode composite layer was calculated by subtracting the film thickness of the copper foil from the calculated average value of the obtained measured values.

[0110] <Weight of negative electrode mixture layer> The basis weight is the mass per unit area of ​​the negative electrode mixture layer, and the basis weight was calculated by determining the mass of the negative electrode mixture layer and the coating area of ​​the negative electrode mixture layer from the negative electrode mixture layer prepared above.

[0111] <Density of negative electrode mixture layer> The density is the mass per unit volume of the negative electrode mixture layer, and was calculated from the basis weight determined above and the thickness of the negative electrode mixture layer obtained above.

[0112] <Flexibility test> The electrode obtained above was cut into a 70 mm x 50 mm MD x TD piece and placed on a 10 mm slit stage so that the 70 mm MD portion of the electrode was the center. The electrode was bent using a 1 mm thick stainless steel blade (100 mm x 100 mm) in a universal testing machine (Shimadzu Corporation, model number: AG-X, test speed: 50 mm / min), and the maximum load (N) was measured. The maximum load (N) during the stiffness / flexibility test was determined by dividing the maximum load (N) by the thickness of the negative electrode composite layer. The larger the maximum load (N / mm) during the softness / rigidity test, the higher the rigidity, and the less likely it is to deform under external force.

[0113] <Making a coin-type battery> [Preparation of electrolyte] As a solvent, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3:7. An electrolyte was prepared by adding LiPF6 as an electrolyte so that the concentration of the final electrolyte solution would be 1 mol / L, and vinylene carbonate (VC) as an additive was added so that the content of the final electrolyte solution would be 1.0 mass%.

[0114] [Preparation of electrodes and separators] The electrode (negative electrode) obtained above was punched out into a disk shape with a diameter of 14 mm, and lithium foil was punched out into a disk shape with a diameter of 13 mm as a positive electrode, to prepare a coin-shaped negative electrode and a coin-shaped positive electrode, respectively. Next, a microporous polyethylene film having a thickness of 20 μm was punched into a disk shape having a diameter of 17 mm to obtain a coin-shaped separator.

[0115] [Fabrication of lithium-ion secondary batteries] The negative electrode, coin-shaped separator, and positive electrode obtained above were stacked in this order in a stainless steel battery can (size 2032). Next, 20 μL of the electrolyte prepared above was poured into the battery can, and the negative electrode, separator, and positive electrode were impregnated with the electrolyte. 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 ion secondary battery) having a diameter of 20 mm and a height of 3.2 mm was fabricated.

[0116] [Aging treatment] The resulting coin-type batteries were charged to 2.5 to 4.2 V at 25°C, 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%), for aging (activation) treatment.

[0117] <Measurement of initial charge capacity and initial discharge capacity, and calculation of initial charge / discharge efficiency> After activation, the coin-type battery was charged to a constant voltage of 4.2 V at 25°C, and the charge capacity (first cycle) was measured. It was then discharged to 2.5 V at a constant current of 0.05 C at 25°C, and the discharge capacity (first cycle) was measured. The ratio of the discharge capacity to the charge capacity obtained above (discharge capacity / charge capacity) was calculated as the initial charge / discharge efficiency.

[0118] [Example 2 and Comparative Examples 1 to 4] An electrode and a battery were produced in the same manner as in Example 1, except that the electrode binder was changed to the raw materials and compositions shown in Table 1, and then evaluated.

[0119] [Table 1]

[0120] It can be seen that the electrodes of Examples 1 and 2 are less susceptible to deformation due to external forces than the electrodes of Comparative Examples 1 to 4. It can also be seen that the lithium ion secondary batteries equipped with the electrodes of Examples 1 and 2 are excellent in battery characteristics (i.e., initial charge capacity, initial discharge capacity, and initial charge / discharge efficiency).

Claims

1. An electrode binder comprising olefin polymer particles (A) satisfying the following requirements (i) to (iii): (i) The intrinsic viscosity [η] measured in decalin solvent at 135°C is in the range of 1 to 10 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) The amount passing through a 45 μm mesh sieve is 50% by mass or more.

2. 2. The electrode binder according to claim 1, wherein the average particle diameter d50 of the olefin polymer particles (A) is in the range of 1 to 15 μm.

3. The electrode binder according to claim 1 , wherein the olefin-based polymer particles (A) are ethylene-based polymer particles.

4. An electrode comprising the electrode binder according to any one of claims 1 to 3 and an active material.

5. 5. The electrode of claim 4, which is a negative electrode.

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

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

8. A step of dry-mixing the electrode binder according to any one of claims 1 to 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:

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