Positive electrode for lithium-ion batteries and method for manufacturing same

Abstract

A positive electrode for a lithium ion battery, comprising a current collector and a positive electrode composition layer provided on a surface of the current collector, wherein the current collector and the positive electrode composition layer are not adhered to each other, the positive electrode composition layer contains coated positive electrode active material particles and a conductive aid, wherein at least a part of a surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A) that is any one of a copolymer (A1) having a methacrylic acid, a lauryl methacrylate, and a 1,6-hexanediol dimethacrylate as constituent monomers, a copolymer (A2) having an isobornyl methacrylate and a 1,6-hexanediol dimethacrylate as constituent monomers, or a copolymer (A3) having a lauryl methacrylate, a 2-ethylhexyl methacrylate, and a 1,6-hexanediol dimethacrylate as constituent monomers, a weight proportion of the 1,6-hexanediol dimethacrylate contained in the constituent monomers of the copolymer is 0.2 to 1% by weight based on the total weight of the constituent monomers of the copolymer, and a weight average molecular weight of the polymer compound (A) is 300,000 or less.

Description

Technical Field

[0001] This invention relates to a positive electrode for lithium-ion batteries and a method for manufacturing the same. Background Technology

[0002] In recent years, lithium-ion batteries, as rechargeable batteries capable of achieving high energy density and high output density, have been widely used in various applications. Furthermore, with the expansion of applications, the demand for increasing the capacity of lithium-ion batteries has increased.

[0003] One method for increasing the capacity of lithium-ion batteries is to increase the electrode area. However, typically, increasing the electrode area of ​​a lithium-ion battery leads to a greater impact on the volume change of the electrode active material layer during charging and discharging, and the electrode active material layer is prone to self-destruction or peeling off from the surface of the current collector. Therefore, it is difficult to improve cycle characteristics.

[0004] PTL1 discloses a method for providing a pressure relaxation layer between the current collector and the electrode active material layer to address issues related to volume changes in the electrode active material layer during charging and discharging. Furthermore, PTL2 discloses a method for mitigating electrode volume changes by coating the surface of the electrode active material with a resin that has a liquid absorption rate of at least 10% when immersed in an electrolyte solution and a tensile elongation at break of at least 10% in a saturated liquid absorption state.

[0005] Reference List

[0006] Patent documents

[0007] PTL1: Japanese Patent Publication No. 2018-101624

[0008] PTL2: International Publication No. 2015 / 5117 Summary of the Invention

[0009] Technical issues

[0010] However, it cannot be said that the methods disclosed in PTL1 and PTL2 are sufficiently effective for large-area electrodes that are significantly affected by volume changes in the electrode active material layer. Furthermore, from the viewpoint of energy density and cycling characteristics, there is room for further improvement.

[0011] Specifically, the present invention was made in view of the foregoing circumstances, and its object is to provide a positive electrode for lithium-ion batteries that has excellent energy density and cycle characteristics and whose area can be increased.

[0012] Solution to the problem

[0013] As a result of careful research to solve the above-mentioned problems, the inventors of this invention have completed this invention. Specifically, this invention relates to a positive electrode for a lithium-ion battery, comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector, wherein the current collector and the positive electrode composition layer are not adhered to each other, the positive electrode composition layer contains coated positive electrode active material particles and conductive additives, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A), the polymer compound (A) being any of the following: a copolymer (A1) having methacrylic acid, lauryl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers; having A copolymer (A2) comprising isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers; or a copolymer (A3) comprising lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers, wherein the weight percentage of 1,6-hexanediol dimethacrylate contained in the constituent monomers of the copolymer is 0.2% to 1% by weight, and the polymer compound (A) has a weight-average molecular weight of 300,000 or less, and also relates to a formulation for a positive electrode of a lithium-ion battery. A method for manufacturing a positive electrode for a lithium-ion battery, comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector, the method comprising the steps of: preparing a positive electrode composition layer by compression molding of a positive electrode composition containing coated positive electrode active material particles and a conductive additive, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A); and repositioning the positive electrode composition layer on the current collector, wherein the polymer compound (A) is any one of the following: having methacrylic acid, lauryl methacrylate and 1,6-hexanediol dimethylpropyl A copolymer having an acrylate as a constituent monomer (A1); a copolymer having isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A2); or a copolymer having lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A3), wherein the weight percentage of 1,6-hexanediol dimethacrylate contained in the constituent monomers of the copolymer is 0.2% to 1% by weight, and the polymer compound (A) has a weight average molecular weight of 300,000 or less.

[0014] Beneficial effects of the present invention

[0015] According to the present invention, a positive electrode for lithium-ion batteries with high energy density and excellent cycle characteristics can be obtained, and its area can be increased. Detailed Implementation

[0016] The invention will be described in detail below.

[0017] In this specification, the concept of lithium-ion rechargeable batteries should also be included where applicable.

[0018] The positive electrode for a lithium-ion battery of the present invention comprises a current collector and a positive electrode composition layer disposed on the surface of the current collector, wherein the current collector and the positive electrode composition layer are not adhered to each other, the positive electrode composition layer contains coated positive electrode active material particles and conductive additives, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A), the polymer compound (A) being any one of the following: having methacrylic acid, lauryl methacrylate and 1,6-hexanediol dimethacrylate as constituents. A copolymer of monomers (A1); a copolymer having isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A2); or a copolymer having lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A3), wherein the weight percentage of 1,6-hexanediol dimethacrylate contained in the constituent monomers of the copolymer is 0.2% to 1% by weight, and the polymer compound (A) has a weight average molecular weight of 300,000 or less.

[0019] The positive electrode used in lithium-ion batteries has a current collector.

[0020] Examples of materials that constitute current collectors include metallic materials such as copper, aluminum, titanium, stainless steel, nickel and their alloys, calcined carbon, conductive polymer materials, conductive glass, etc.

[0021] Among these materials, conductive polymer materials are preferred from the viewpoints of weight reduction, corrosion resistance, and high conductivity.

[0022] The shape of the current collector is not particularly limited, and it can be a sheet-like current collector made of the aforementioned materials. Alternatively, the current collector can be a deposition layer made of microparticles composed of the aforementioned materials.

[0023] There is no particular limitation on the thickness of the current collector, but it is preferably 50 μm to 500 μm.

[0024] The current collector is preferably a resin current collector made of conductive polymer material.

[0025] As a conductive polymer material constituting the resin current collector, conductive polymers or resins with conductive agents added as needed can be used, for example.

[0026] Examples of conductive agents constituting conductive polymer materials include metal-based conductive additives [aluminum, stainless steel (SUS), silver, gold, copper, titanium and alloys containing these metals], carbon-based conductive additives [graphite and carbon black (acetylene black, Ketjen black, furnace black, channel black, thermal lamp black, etc.)], and mixtures thereof.

[0027] One of these conductive additives can be used alone, or two or more of them can be used in combination.

[0028] From the viewpoint of electrical stability, aluminum, stainless steel, silver, gold, copper, titanium, carbon-based conductive additives, or mixtures thereof are preferred, silver, gold, aluminum, stainless steel, or carbon-based conductive additives are more preferred, and carbon-based conductive additives are particularly preferred.

[0029] Furthermore, these conductive additives can be those obtained by coating a conductive material [preferably a metallic conductive material in the material of the aforementioned conductive additive] around a particle-based ceramic or resin material using methods such as plating.

[0030] There is no particular limitation on the average particle size of the conductive additive; however, from the viewpoint of the electrical characteristics of the battery, it is preferably 0.01 μm to 10 μm, more preferably 0.02 μm to 5 μm, and still more preferably 0.03 μm to 1 μm. Herein, “particle size” means the maximum distance L between any two points on the outline of the conductive additive. The value of “average particle size” should be the average of the particle sizes observed in several to dozens of fields of view using an observation device such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0031] The shape (morphology) of conductive additives is not limited to particulate form; it can be any form other than particulate form, and it can be the form used in practical applications as so-called filler-based conductive additives such as carbon nanotubes.

[0032] Conductive additives can be conductive fibers in the form of fibers.

[0033] Examples of conductive fibers include carbon fibers such as PAN-based carbon fibers or pitch-based carbon fibers; conductive fibers obtained by uniformly dispersing a metal or graphite with good conductivity in synthetic fibers; metal fibers obtained by making fibers from metals such as stainless steel; conductive fibers obtained by coating the surface of organic fibers with a metal; and conductive fibers obtained by coating the surface of organic fibers with a resin containing a conductive substance. Among these conductive fibers, carbon fibers are preferred. Furthermore, polypropylene resins in which graphene is kneaded are also preferred.

[0034] When the conductive additive is a conductive fiber, its average fiber diameter is preferably from 0.1 μm to 20 μm.

[0035] From the viewpoint of the dispersibility of the conductive additive, the content of the conductive additive is preferably 1 wt% to 79 wt%, more preferably 2 wt% to 30 wt%, and still preferably 5 wt% to 25 wt%.

[0036] Examples of resins constituting conductive polymer materials include polyethylene, polypropylene, polymethylpentene, polycyclic olefins, polyethylene terephthalate, polyether nitrile, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylonitrile, polymethyl acrylate, polymethyl methacrylate, polyvinyl fluoride, epoxy resin, silicone resin, or mixtures thereof.

[0037] From the viewpoint of electrical stability, polyethylene, polypropylene, polymethylpentene, and polycyclic olefins are preferred, and polyethylene, polypropylene, and polymethylpentene are more preferred.

[0038] From the viewpoint of resin strength, based on the weight of the resin current collector, the content of the resin constituting the conductive polymer material is preferably 20% to 98% by weight, more preferably 40% to 95% by weight, and still preferably 60% to 92% by weight.

[0039] The aforementioned resin current collector can be manufactured, for example, by the following method.

[0040] First, materials for resin current collectors are obtained by mixing resin, conductive additives, and other components as needed.

[0041] Examples of mixing methods include methods for obtaining a masterbatch of conductive filler and then further mixing it with resin, methods using a masterbatch of resin, conductive additives and other components as needed, and methods for mixing all raw materials together. For mixing, suitable known mixers for mixing granular or powdered components can be used, such as kneaders, internal mixers, Banbury mixers and rollers.

[0042] There are no particular restrictions on the order in which each component is added during mixing. The resulting mixture can be further granulated or powdered using a granulator.

[0043] The obtained material for the current collector is formed into, for example, a film, thereby obtaining the aforementioned resin current collector. Examples of methods for forming into a film include the T-die method, blow molding, calendering, and other known film-forming methods. The aforementioned resin current collector can also be obtained by molding methods other than film forming.

[0044] The positive electrode for lithium-ion batteries of the present invention has a positive electrode composition layer.

[0045] The positive electrode composition layer does not adhere to the current collector.

[0046] The above-mentioned positive electrode composition layer contains coated positive electrode active material particles and conductive additives, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing polymer compound (A).

[0047] Examples of the aforementioned positive electrode active material particles include composite oxides of lithium and transition metals {composite oxides having one transition metal (LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, LiMn2O4, etc.), and composite oxides having two transition metal elements (e.g., LiFeMnO4, LiNi...} 1-x CoxO2, LiMn 1-y Co y O2, LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2), a complex oxide having three or more metallic elements [e.g., LiM] a M' b M” c O2 (where M, M', and M" are distinct transition metal elements satisfying a + b + c = 1, and an example is LiNi) 1 / 3 Mn 1 / 3 Co 1 / Lithium-containing transition metal phosphates (e.g., LiFePO4, LiCoPO4, LiMnPO4, or LiNiPO4), transition metal oxides (e.g., MnO2 and V2O5), transition metal sulfides (e.g., MoS2 or TiS2), and conductive macromolecules (e.g., polyaniline, polypyrrole, polythiophene, polyacetylene, poly(p-phenylene), or polyvinylcarbazole). Two or more of these can be used in combination.

[0048] Here, a lithium-containing transition metal phosphate can be a lithium-containing transition metal phosphate in which a portion of the transition metal site is replaced by another transition metal.

[0049] From the viewpoint of battery characteristics, the average particle size of the positive electrode active material particles is preferably 0.01 μm to 100 μm, more preferably 0.1 μm to 35 μm, and still more preferably 2 μm to 30 μm.

[0050] The volume-average particle size of positive electrode active material particles refers to the particle size at the 50% integral value in the particle size distribution obtained by the microtrack method (laser diffraction / scattering method) (Dv50). The laser diffraction method determines the particle size distribution by using the scattered light obtained from irradiating particles with a laser. The volume-average particle size can be measured using a laser diffraction / scattering type particle size distribution measurement device [MICROTRAC, available from MicrotracBEL Corp.].

[0051] The polymer compound (A) is any one of the following: a copolymer having methacrylic acid, lauryl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A1), a copolymer having isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A2), or a copolymer having lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A3).

[0052] Based on the total weight of the constituent monomers of the copolymers, the weight percentage of 1,6-hexanediol dimethacrylate contained in the constituent monomers of the copolymers (A1), (A2), and (A3) is 0.2% to 1% by weight. If the weight percentage of 1,6-hexanediol dimethacrylate in the copolymers (A1), (A2), and (A3) is less than 0.2% by weight, the resin swells due to the electrolyte solution in the battery and therefore does not exhibit sufficient strength to fix the position of the positive electrode active material particles in the positive electrode composition layer; if the weight percentage exceeds 1% by weight, the adhesiveness of the resin deteriorates and therefore cannot exhibit sufficient strength to fix the position of the positive electrode active material particles in the positive electrode composition layer.

[0053] The weight proportion of 1,6-hexanediol dimethacrylate contained in the constituent monomers of the above copolymers (A1), (A2) and (A3) can be measured by dissolving the copolymers in a supercritical fluid and analyzing the oligomer components by gas chromatography-mass spectrometry (GC-MS).

[0054] The weight-average molecular weight of the polymer compound (A) described above [hereinafter abbreviated as Mw: the measurement is based on gel permeation chromatography (GPC) as described later] is 300,000 or less. If the Mw of the polymer compound (A) exceeds 300,000, the viscosity of the resin solution increases too much, and therefore a good coating cannot be obtained.

[0055] The Mw of polymer compound (A) is preferably 200,000 or less, and more preferably 150,000 or less. The Mw of polymer compound (A) is preferably 30,000 or more, and more preferably 60,000 or more.

[0056] The measurement conditions for Mw measured by GPC in this invention are as follows.

[0057] Apparatus: High-temperature gel permeation chromatography [“Alliance GPC V2000”, available from Waters Corporation]; Solvent: o-dichlorobenzene

[0058] Standard material: polystyrene

[0059] Sample concentration: 3 mg / ml

[0060] Column solid phase: PLgel 10μm, MIXED-B, two columns in series (Polymer Laboratories Limited)

[0061] Column temperature: 135℃

[0062] The polymer compound (A) described above can be manufactured using known polymerization initiators {azo initiators [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylpentanonitrile, etc.)], peroxide initiators (benzoyl peroxide, di-tert-butyl peroxide, lauryl peroxide, etc.)} via known polymerization methods (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.).

[0063] From the viewpoint of adjusting Mw to a preferred range, the amount of polymerization initiator used, based on the total weight of monomers, is preferably 0.01% to 5% by weight, more preferably 0.05% to 2% by weight, and even more preferably 0.1% to 1.5% by weight. Although the polymerization temperature and polymerization time are adjusted according to the type of polymerization initiator, the polymerization temperature is preferably -5°C to 150°C (more preferably 30°C to 120°C), and the reaction time is preferably 0.1 hours to 50 hours (more preferably 2 hours to 24 hours).

[0064] Examples of solvents used in solution polymerization include esters (C2-C8, such as ethyl acetate and butyl acetate), alcohols (C1-C8, such as methanol, ethanol, and octanol), hydrocarbons (C4-C8, such as n-butane, cyclohexane, and toluene), and ketones (C3-C9, such as methyl ethyl ketone). From the viewpoint of adjusting the molecular weight to a preferred range, the amount used, based on the total weight of the monomers, is preferably 5% to 900% by weight, more preferably 10% to 400% by weight, and particularly preferably 30% to 300% by weight, and the monomer concentration is preferably 10% to 95% by weight, more preferably 20% to 90% by weight, and particularly preferably 30% to 80% by weight.

[0065] Examples of dispersion media in emulsion polymerization and suspension polymerization include water, alcohols (such as ethanol), esters (such as ethyl propionate), and light naphtha, while examples of emulsifiers include metal salts of higher fatty acids (C10-C24) (such as sodium oleate and sodium stearate), metal salts of sulfated esters of higher alcohols (C10-C24) (such as sodium dodecyl sulfate), ethoxylated tetramethyldecanediol, sodium ethyl methacrylate, and dimethylaminomethyl methacrylate. Furthermore, polyvinyl alcohol and polyvinylpyrrolidone can be added as stabilizers.

[0066] In solution polymerization, the monomer concentration in the solution, and in emulsion polymerization and suspension polymerization, the monomer concentration in the dispersion is preferably 5% to 95% by weight, more preferably 10% to 90% by weight, and still more preferably 15% to 85% by weight. Based on the total weight of the monomers, the amount of polymerization initiator used is preferably 0.01% to 5% by weight, more preferably 0.05% to 2% by weight.

[0067] For polymerization, known chain transfer agents can be used, such as mercapto compounds (dodecyl mercaptan, n-butyl mercaptan, etc.) and / or halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.).

[0068] In the coated positive electrode active material particles, at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A). If necessary, the coating layer may further contain a conductive material.

[0069] The weight ratio of the polymer compound (A) relative to the weight of the positive electrode active material particles is not particularly limited, but from the viewpoint of fixing the position of the coated positive electrode active material particles and from the viewpoint of the formability of the positive electrode composition layer, it is preferably 0.1% to 10% by weight.

[0070] For example, the above-mentioned coated positive electrode active material particles can be obtained as follows: while stirring the above-mentioned positive electrode active material at 30 rpm to 50 rpm in a general mixer, a resin solution containing the above-mentioned polymer compound (A) is added dropwise over 1 minute to 90 minutes; a conductive additive is further added as needed; while stirring the mixture, the temperature is raised to 50°C to 200°C and the pressure is reduced to 0.007 MPa to 0.04 MPa; and the mixture is then kept in this state for 10 minutes to 150 minutes.

[0071] The above-described positive electrode composition layer contains a conductive additive. As the conductive additive, the same conductive additive contained in the above-described resin current collector can be appropriately used.

[0072] From the viewpoint of electrical characteristics, the weight percentage of conductive additives contained in the positive electrode composition layer is preferably 0.1% to 10% by weight, based on the weight of the positive electrode composition layer.

[0073] The aforementioned conductive additive may be contained in a coating layer covering the positive electrode active material particles, or it may be contained in a layer other than the aforementioned coating layer.

[0074] There is no particular limitation on the thickness of the above-mentioned positive electrode composition layer, but from the viewpoint of energy density, it is preferably 100 μm to 800 μm.

[0075] In the positive electrode of the lithium-ion battery of the present invention, the current collector and the positive electrode composition layer do not adhere to each other. Therefore, even if the volume of the positive electrode composition layer changes due to charging and discharging, the current collector will not change accordingly, and thus self-destruction of the positive electrode composition layer and irreversible peeling of the current collector are impossible.

[0076] In this invention, the fact that the current collector and the positive electrode composition layer do not adhere to each other means that the adhesive strength between the current collector and the positive electrode composition layer is 20 N or less. The adhesive strength between the current collector and the positive electrode composition layer can be measured using the JIS K 6850:1999 adhesive strength test. The measurement conditions are as follows.

[0077] Test environment: 25℃, 50% humidity

[0078] Measuring device: Shimadzu AUTOGRAPH AGS-10kNX

[0079] Measurement conditions: As the test specimen, a current collector was used instead of a JIS-standard metal plate. To reproduce the internal environment of the battery cell, measurements were taken at 1 kgf / cm² on the bonding surface of the current collector and the positive electrode composition layer. 2 Measurements were taken under load.

[0080] [Method for Manufacturing a Positive Electrode for a Lithium-ion Battery] The method for manufacturing a positive electrode for a lithium-ion battery according to the present invention is a method for manufacturing a positive electrode for a lithium-ion battery, the positive electrode for the lithium-ion battery comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector, the method comprising the steps of: preparing a positive electrode composition layer by compressing a positive electrode composition containing coated positive electrode active material particles and a conductive additive, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A); and repositioning the positive electrode composition layer on the current collector, wherein the polymer compound (A) is any of the following: having A copolymer of methacrylic acid, lauryl methacrylate, and 1,6-hexanediol dimethacrylate as constituent monomers (A1); a copolymer of isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A2); or a copolymer of lauryl methacrylate, 2-ethylhexyl methacrylate, and 1,6-hexanediol dimethacrylate as constituent monomers (A3), wherein the weight percentage of 1,6-hexanediol dimethacrylate contained in the constituent monomers of the copolymer is 0.2% to 1% by weight based on the total weight of the constituent monomers of the copolymer, and the weight average molecular weight of the polymer compound (A) is 300,000 or less.

[0081] The method for manufacturing a positive electrode for a lithium-ion battery according to the present invention includes the step of preparing a positive electrode composition layer by compressing a positive electrode composition containing coated positive electrode active material particles and conductive additives, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A).

[0082] Compression molding can be performed using any pressurizing device and pressurizing fixture, such as a hydraulic device. For example, the positive electrode composition is loaded into a cylindrical bottom container, a cylindrical rod-shaped pressurizing fixture with a diameter slightly smaller than the inner diameter of the bottom container is inserted from above, and then compressed by the pressurizing device, thereby obtaining a layer of positive electrode composition as a cylindrical molded body.

[0083] By changing the shape of the pressure fixture, molded bodies of any shape can be obtained.

[0084] As the compression condition in compression molding, the pressure applied to the positive electrode composition is preferably from 100 MPa to 3000 MPa. The pressurization time is preferably from 1 second to 300 seconds.

[0085] The compression molding steps described above can be performed on the current collector or on a release material other than the current collector. There are no particular limitations on the release material, and known release papers or release films can be appropriately selected and used.

[0086] Examples of release materials include release papers such as cellophane, kraft paper, and clay-coated paper, and release films made from non-fluorinated resins such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene, and polyimide (PI), or from fluorinated resins such as polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-hexafluoropropylene copolymer, perfluoroalkoxyalkane (PFA), and polyvinylidene fluoride (PVdF).

[0087] The method for manufacturing a positive electrode for a lithium-ion battery according to the present invention includes a step of repositioning the positive electrode composition layer obtained in the above compression molding step onto a current collector.

[0088] There are no particular limitations on the method for repositioning the positive electrode composition layer onto the current collector, and known transfer methods can be used. For example, a positive electrode for lithium-ion batteries can be obtained by laminating the positive electrode composition layer, which is formed on a release material in a compression molding step, onto the current collector and then peeling off the release material.

[0089] Example

[0090] The invention will be described in particular with reference to specific examples; however, the invention is not limited to these examples without departing from its spirit. Unless otherwise stated, parts refer to parts by weight, and % refers to percentages by weight.

[0091] <Manufacturing Example 1-1: Manufacturing of Polymer Compound (A-1)>

[0092] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 4.6 parts of methacrylic acid, 95.0 parts of lauryl methacrylate, 0.4 parts of 1,6-hexanediol dimethacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours using a dropping funnel to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C, and the initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise through a dropping funnel over 2 hours with stirring. After the addition, the reaction was continued for 3 hours to obtain a copolymer compound (A-1) for coating with a resin concentration of 30%.

[0093] <Manufacturing Example 1-2: Manufacturing of Polymer Compound (A-2)>

[0094] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 99.55 parts of isobornyl methacrylate, 0.45 parts of 1,6-hexanediol dimethacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours using a dropping funnel to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C, and the initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise through a dropping funnel over 2 hours with stirring. After the addition, the reaction was continued for 3 hours to obtain a coating copolymer compound (A-2) with a resin concentration of 30%.

[0095] <Manufacturing Examples 1-3: Manufacturing of Polymer Compound (A-3)>

[0096] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 29.5 parts of lauryl methacrylate, 70.0 parts of 2-ethylhexyl methacrylate, 0.5 parts of 1,6-hexanediol dimethacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours using a dropping funnel to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C, and the initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise through a dropping funnel over 2 hours with stirring. After the addition, the reaction was continued for 3 hours to obtain a coating copolymer compound (A-3) with a resin concentration of 30%.

[0097] <Manufacturing Examples 1-4: Manufacturing of Polymer Compound (A'-1)>

[0098] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 69.5 parts of 2-ethylhexyl methacrylate, 30.0 parts of Ω-methacryloyl-polymethyl methacrylate, 0.5 parts of 1,6-hexanediol dimethacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours using a dropping funnel to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C, and the initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise through a dropping funnel over 2 hours with stirring. After the addition, the reaction was continued for 3 hours to obtain a coating copolymer compound (A'-1) with a resin concentration of 30%.

[0099] <Manufacturing Examples 1-5: Manufacturing of Polymer Compound (A'-2)>

[0100] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 20.0 parts of isobornyl methacrylate, 49.5 parts of 2-ethylhexyl acrylate, 30.0 parts of butyl methacrylate, 0.5 parts of 1,6-hexanediol dimethacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C, and the initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise through a dropping funnel over 2 hours with stirring. After the addition, the reaction was continued for 3 hours to obtain a coating copolymer compound (A'-2) with a resin concentration of 30%.

[0101] <Manufacturing Examples 1-6: Manufacturing of Polymer Compound (A'-3)>

[0102] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 4.75 parts of methacrylic acid, 95.15 parts of lauryl methacrylate, 0.10 parts of 1,6-hexanediol dimethacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours using a dropping funnel to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C, and the initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise through a dropping funnel over 2 hours with stirring. After the addition, the reaction was continued for 3 hours to obtain a coating copolymer compound (A'-3) with a resin concentration of 30%.

[0103] [Table 1-1]

[0104]

[0105] <Manufacturing Examples 1-7: Manufacturing of Coated Positive Electrode Active Material Particles (CA-1)>

[0106] 96 parts of positive electrode active material powder (C-1) (LiNi) 0.8 Co 0.15 Al 0.05 O2 powder (volume average particle size: 4 μm) was placed in a general-purpose mixer, a high-speed mixer FS25 [manufactured by EARTHTECHNICA Co., Ltd.], and while the powder was being stirred at room temperature and 720 rpm, 6.667 parts of a polymer compound solution (A-1) for coating obtained in Manufacturing Example 1-1 was added dropwise over 2 minutes, and the resulting mixture was then further stirred for 5 minutes.

[0107] Next, while the mixture was stirred, 2.0 parts of acetylene black [DENKA BLACK (registered trademark) manufactured by Denka Company Limited] were added in portions over 26 minutes as a conductive additive, and stirring was continued for 30 minutes. Then, while maintaining stirring, the pressure was reduced to 0.01 MPa, and then the temperature was increased to 140°C while maintaining stirring and pressure reduction. The stirring, pressure reduction, and temperature were maintained for 8 hours to distill off volatile substances. The resulting powder was graded using a 212 μm sieve to obtain coated positive electrode active material particles (CA-1).

[0108] Except for changing the polymer compound solution (A-1) used for the coating layer to (A-2) to (A-3) and (A'-1) to (A'-3), respectively, coated positive electrode active material particles (CA-2) to (CA-3) and (CA'-1) to (CA'-3) were obtained using the same procedure as in manufacturing Examples 1-7. Details of the combination are shown in Tables 1-2.

[0109] <Manufacturing Examples 1-8: Manufacturing of Coated Positive Electrode Active Material Particles (CA-4)>

[0110] 91.5 parts of positive electrode active material powder (C-1) (LiNi) 0.8 Co 0.15 Al 0.05 O2 powder (volume average particle size: 4 μm) was placed in a general-purpose mixer, a high-speed mixer FS25 [manufactured by Alstec Corporation], and while the powder was being stirred at room temperature and 720 rpm, 7.0 parts of the coating polymer compound solution (A-1) obtained in Manufacturing Example 1-1 were added dropwise over 2 minutes, and the resulting mixture was then stirred for another 5 minutes.

[0111] Next, while the mixture was stirred, 6.4 parts of acetylene black [DENKA BLACK (registered trademark) manufactured by Denka Company Limited] were added in portions over 26 minutes as a conductive additive, and stirring was continued for 30 minutes. Then, while maintaining stirring, the pressure was reduced to 0.01 MPa, and then the temperature was increased to 140°C while maintaining stirring and pressure reduction. The stirring, pressure reduction, and temperature were maintained for 8 hours to distill off volatile substances. The resulting powder was graded using a 212 μm sieve to obtain coated positive electrode active material particles (CA-4).

[0112] Except that the polymer compound solution (A-1) used for the coating layer is changed to (A-2) to (A-3) and (A'-4) to (A'-6), coated positive electrode active material particles (CA-5) to (CA-6) and (CA'-1) to (CA'-3) are obtained by the same procedure as in manufacturing examples 1-8. Details of the combination are shown in Tables 1-2.

[0113] <Manufacturing Examples 1-9: Manufacturing of Electrolyte Solutions>

[0114] LiPF6 was dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (volume ratio 1:1) at a ratio of 1 mol / L to obtain an electrolyte solution for lithium-ion batteries.

[0115] <Manufacturing Examples 1-10: Fabrication of Current Collectors>

[0116] In a twin-screw extruder, 10 parts of the product “SunAllomer PB522M” [available from SunAllomer Ltd.], 25 parts of the product “SunAllomer PM854X” [available from SunAllomer Ltd.], 10 parts of the product “Suntec B680” [available from Asahi Kasei Chemicals Corporation], 40 parts of graphite granules “SNG-WXA1”, 10 parts of acetylene black 1 “Ensaco 250G”, and 5 parts of the product “Youmex 1001 (acid-modified polypropylene)” [available from Sanyo Chemical Industries, Ltd.] were melt-kneaded at 180°C and 100 rpm for a residence time of 5 minutes to obtain a material for resin current collectors.

[0117] The obtained material for the resin current collector is passed through a T-die extruder and then rolled by a hot press with the temperature controlled at 50°C to obtain the resin current collector.

[0118] <Example 1-1>

[0119] 5g of coated positive electrode active material particles (CA-1) obtained in Manufacturing Examples 1-7, 0.026g of carbon fiber [Donna Carbo Milled S-242, available from Osaka Gas Chemicals Co., Ltd.] as a conductive additive, and 0.2632g of flake graphite [UP-5-α, available from Nippon Graphite Co., Ltd.] were mixed at 1,500 rpm for 3 minutes using a planetary stirring type mixing and kneading apparatus {Awatori Rentaro [THINKY Corporation]}.

[0120] In addition, after adding 0.14 g of the electrolyte solution prepared in Manufacturing Examples 1-9, the mixture was mixed with Awatori Rentaro at 1,500 rpm for 1 minute, mixed twice, and a total of 0.28 g of electrolyte solution was added to obtain the positive electrode composition.

[0121] Weigh 0.217g of the above positive electrode composition and place it in a cylindrical bottom container with an inner diameter of 15mm. Then compress it with a pressure device to obtain a cylindrical negative electrode composition layer (CE-1).

[0122] The pressurization conditions are a pressurization pressure of 150 MPa and a pressurization time of 5 seconds, and the temperature of the pressurization device (pressurization clamp) is 20°C, which is equal to the room temperature during pressurization.

[0123] <Examples 1-2 to 1-6, Comparison of Examples 1-1 and 1-6>

[0124] Except that the coated positive electrode active material particles (CA-1) are changed to coated positive electrode active material particles (CA-2) to (CA-6) and (CA'-1) to (CA'-6), the positive electrode composition layers (CE-2) to (CE-6) and (CE'-1) to (CE'-6) are prepared in the same manner as in Example 1-1. Detailed combinations are shown in Table 1-2.

[0125] <Evaluation of battery internal resistance>

[0126] A PP sheet (available from AS ONE) cut into 2cm squares was prepared, with a φ18mm hole in the center. The prepared positive electrode composition layer (CE-1) and a Li foil cut into φ15mm pieces were stored in the φ18mm hole in the center of the PP sheet, with the layer and foil positioned at the electrode end through a PP separator (available from Celgard, LLC). A 110% electrolyte solution was injected relative to the gap between the positive electrode composition layer (CE-1) and the separator. A resin current collector obtained in Manufacturing Examples 1-10 and a 2cm square copper foil were placed on the outer sides of the positive electrode composition layer (CE-1) and the Li foil, respectively. The cells were then heat-sealed under reduced pressure to prepare an evaluation battery.

[0127] At this point, a 2cm square Al foil with leads is applied to the resin current collector, and a 2cm square Cu foil with leads is applied to the copper foil. While only exposing the leads, a reduced-pressure heat seal is performed using an aluminum lamination. Each lead is connected to the charge / discharge device "HJ0501SM8A" [available from HOKUTO DENKO Corporation], and the DCR is evaluated under the following conditions.

[0128] The cells were charged to up to 4.2V at 1C under CC-CV (cutoff current 0.01C) conditions and then discharged to up to 2.5V at 0.1C after a 1-hour pause. The internal resistance of each cell was evaluated, with V0 as the voltage immediately before discharge, V1 as the voltage after discharge, I1 as the current during discharge, and (V-V0) / I1 as the DC resistance (DCR). The evaluation was performed under the following criteria. The results are described in Tables 1-2.

[0129] ◎: DCR less than 15 Ω·cm 2

[0130] ○: DCR is 15 Ω·cm 2 Or larger, less than 21 Ω·cm 2

[0131] Δ: DCR is 21 Ω·cm 2 Or larger, less than 26 Ω·cm 2

[0132] ×: DCR is 26Ω·cm 2 or larger

[0133] <Evaluation of Cyclic Characteristics>

[0134] Similar to DCR evaluation, the battery to be evaluated is connected to a charge / discharge device, and its cycle characteristics are evaluated under the following conditions.

[0135] The capacitor was charged to 4.2V at 1C under CC-CV (cutoff current 0.01C) conditions, and then discharged to 2.5V at 0.1C after a 1-hour pause. This discharge capacity was set as the initial capacity X0. This process was repeated 50 times to obtain the discharge capacity X1 of the 50th cycle. The cycle characteristics were evaluated using X1 / X0 as the discharge capacity retention rate after 50 cycles. The evaluation was performed under the following criteria. The results are described in Tables 1-2.

[0136] ◎: Discharge capacity retention rate of 97% or greater

[0137] ○: Discharge capacity retention is 93% or greater, but less than 97%.

[0138] Δ: Discharge capacity retention is 89% or greater, but less than 93%.

[0139] ×: Discharge capacity retention is less than 89%.

[0140] [Table 1-2]

[0141]

[0142] The results in Table 1-2 show that lithium-ion batteries manufactured using the cathode material for lithium-ion batteries have low internal resistance and excellent cycle characteristics.

[0143] [Negative electrode for lithium-ion batteries and method for manufacturing negative electrode for lithium-ion batteries]

[0144] The negative electrode for lithium-ion batteries and its manufacturing method will then be described.

[0145] The methods disclosed in PTL1 and PTL2 are not sufficiently effective for large-area electrodes where volume changes in the electrode active material layer have a significant impact. Further improvements are possible in terms of energy density and cycling characteristics.

[0146] The following negative electrode for lithium-ion batteries was developed to solve the above problems; the negative electrode for lithium-ion batteries has excellent energy density and cycle characteristics, and its surface area can be increased.

[0147] The negative electrode for a lithium-ion battery has a current collector and a negative electrode composition layer disposed on the surface of the current collector, wherein the current collector and the negative electrode composition layer are not adhered to each other; the negative electrode composition layer contains coated negative electrode active material particles and conductive additives, wherein at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing a polymer compound (B); the polymer compound (B) is a copolymer containing at least one monomer selected from the group consisting of acrylic acid and 2-ethylhexyl methacrylate as essential constituent monomers; and based on the total weight of the constituent monomers of the copolymer, the total weight ratio of acrylic acid and 2-ethylhexyl methacrylate is 60% or more by weight.

[0148] The negative electrode used in lithium-ion batteries has a current collector.

[0149] Examples of materials that constitute current collectors include metallic materials such as copper, aluminum, titanium, stainless steel, nickel and their alloys, calcined carbon, conductive polymer materials, conductive glass, etc.

[0150] Among these materials, conductive polymer materials are preferred from the viewpoints of weight reduction, corrosion resistance, and high conductivity.

[0151] The shape of the current collector is not particularly limited, and it can be a sheet-like current collector made of the aforementioned materials. Alternatively, the current collector can be a deposition layer made of microparticles composed of the aforementioned materials.

[0152] There is no particular limitation on the thickness of the current collector, but it is preferably 50 μm to 500 μm.

[0153] The current collector is preferably a resin current collector made of conductive polymer material.

[0154] As a conductive polymer material constituting the resin current collector, conductive polymers or resins with conductive agents added as needed can be used, for example.

[0155] Examples of conductive agents constituting conductive polymer materials include metal-based conductive additives [aluminum, stainless steel (SUS), silver, gold, copper, titanium and alloys containing these metals], carbon-based conductive additives [graphite and carbon black (acetylene black, Ketjen black, furnace black, channel black, thermal lamp black, etc.)], and mixtures thereof.

[0156] These conductive additives can be used alone, or in combination of two or more. From the viewpoint of electrical stability, aluminum, stainless steel, silver, gold, copper, titanium, carbon-based conductive additives, or mixtures thereof are preferred, silver, gold, aluminum, stainless steel, or carbon-based conductive additives are more preferred, and carbon-based conductive additives are particularly preferred. Furthermore, these conductive additives can be those obtained by coating a conductive material [preferably a metallic conductive material among the materials of the aforementioned conductive additives] around a particulate-based ceramic or resin material using plating or the like.

[0157] There is no particular limitation on the average particle size of the conductive additive; however, from the viewpoint of the electrical characteristics of the battery, it is preferably 0.01 μm to 10 μm, more preferably 0.02 μm to 5 μm, and still more preferably 0.03 μm to 1 μm. "Particle size" refers to the maximum distance L between any two points on the outline of the conductive additive. The value of "average particle size" should be the average of the particle sizes observed in several to dozens of fields of view using an observation device such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0158] The shape (morphology) of conductive additives is not limited to particulate form; it can be any form other than particulate form, and it can be the form used in practical applications as so-called filler-based conductive additives such as carbon nanotubes.

[0159] Conductive additives can be conductive fibers in the form of fibers.

[0160] Examples of conductive fibers include carbon fibers such as PAN-based carbon fibers or pitch-based carbon fibers; conductive fibers obtained by uniformly dispersing a metal or graphite with good conductivity in synthetic fibers; metal fibers obtained by making fibers from metals such as stainless steel; conductive fibers obtained by coating the surface of organic fibers with a metal; and conductive fibers obtained by coating the surface of organic fibers with a resin containing a conductive substance. Among these conductive fibers, carbon fibers are preferred. Furthermore, polypropylene resins in which graphene is kneaded are also preferred.

[0161] When the conductive additive is a conductive fiber, its average fiber diameter is preferably from 0.1 μm to 20 μm.

[0162] From the viewpoint of the dispersibility of the conductive additive, the content of the conductive additive is preferably 1 wt% to 79 wt%, more preferably 2 wt% to 30 wt%, and still preferably 5 wt% to 25 wt%.

[0163] Examples of resins constituting conductive polymer materials include polyethylene, polypropylene, polymethylpentene, polycyclic olefins, polyethylene terephthalate, polyether nitrile, polytetrafluoroethylene, styrene-butadiene rubber, polyacrylonitrile, polymethyl acrylate, polymethyl methacrylate, polyvinyl fluoride, epoxy resin, silicone resin, or mixtures thereof.

[0164] From the viewpoint of electrical stability, polyethylene, polypropylene, polymethylpentene, and polycyclic olefins are preferred, and polyethylene, polypropylene, and polymethylpentene are more preferred.

[0165] From the viewpoint of resin strength, based on the weight of the resin current collector, the content of the resin constituting the conductive polymer material is preferably 20% to 98% by weight, more preferably 40% to 95% by weight, and still preferably 60% to 92% by weight.

[0166] The aforementioned resin current collector can be manufactured, for example, by the following method.

[0167] First, materials for resin current collectors are obtained by mixing resin, conductive additives, and other components as needed.

[0168] Examples of mixing methods include methods for obtaining a masterbatch of conductive filler and then further mixing it with resin, methods using a masterbatch of resin, conductive additives and other components as needed, and methods for mixing all raw materials together. For mixing, suitable known mixers for mixing granular or powdered components can be used, such as kneaders, internal mixers, Banbury mixers and rollers.

[0169] There are no particular restrictions on the order in which each component is added during mixing. The resulting mixture can be further granulated or powdered using a granulator.

[0170] The obtained material for the current collector is formed into, for example, a film, thereby obtaining the aforementioned resin current collector. Examples of methods for forming into a film include the T-die method, blow molding, calendering, and other known film-forming methods. The aforementioned resin current collector can also be obtained by molding methods other than film forming.

[0171] The negative electrode used in lithium-ion batteries has a negative electrode composition layer.

[0172] The negative electrode composition layer does not adhere to the current collector.

[0173] The aforementioned negative electrode composition layer contains coated negative electrode active material particles and conductive additives, wherein at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing a polymer compound (B).

[0174] There are no particular limitations on the aforementioned negative electrode active material particles, as long as they can be used as negative electrode active materials in lithium-ion batteries. For example, examples of materials constituting negative electrode active materials include carbon-based materials and silicon-based materials. Among them, the negative electrode active material is preferably made of a carbon-based material.

[0175] Examples of carbon-based materials include, for example, graphite, non-graphitizable carbon, amorphous carbon, resin calcination products (e.g., calcination products obtained by calcining and carbonizing phenolic resins, furan resins, etc.), and coke (e.g., pitch coke, needle coke, and petroleum coke). Mixtures of conductive macromolecules (e.g., polyacetylene or polypyrrole), metal oxides (titanium oxide, lithium-titanium oxide, etc.), and metal alloys (e.g., lithium-tin alloys, lithium-aluminum alloys, or aluminum-manganese alloys) with carbon-based materials can be used. For materials that do not contain lithium or lithium ions internally, a portion or all of that internality can be pre-doped to incorporate lithium or lithium ions.

[0176] The silicon-based material is preferably at least one selected from the group consisting of silicon oxide (SiOx), Si-C composites, Si-Al alloys, Si-Li alloys, Si-Ni alloys, Si-Fe alloys, Si-Ti alloys, Si-Mn alloys, Si-Cu alloys, and Si-Sn alloys.

[0177] Examples of Si-C composites include silicon carbide, carbon particles whose surfaces are coated with silicon and / or silicon carbide, and silicon particles and silicon oxide particles whose surfaces are respectively coated with carbon and / or silicon carbide.

[0178] Silicon and / or silicon compound particles can be single particles (also called primary particles) or can form composite particles obtained by aggregating primary particles (i.e., secondary particles obtained by aggregating primary particles composed of silicon and / or silicon compounds). There are two types of composite particles: those where the primary particles of silicon and / or silicon compound particles are aggregated by their adsorption forces, and those where the primary particles are aggregated via adsorption through another material. Examples of methods for forming composite particles by binding primary particles via another material include, for example, methods of mixing primary particles of silicon and / or silicon compound particles with polymer compounds constituting the coating film.

[0179] From the viewpoint of battery characteristics, the average particle size of the negative electrode active material particles is preferably 0.1 μm to 100 μm, more preferably 1 μm to 50 μm, and even more preferably 2 μm to 20 μm.

[0180] The volume-average particle size of anode active material particles refers to the particle size at the 50% integral of the particle size distribution obtained by laser diffraction (laser diffraction / scattering method) (Dv50). Laser diffraction is a method of determining particle size distribution by using scattered light obtained from irradiating particles with a laser. The volume-average particle size can be measured using a laser diffraction / scattering type particle size distribution measurement device [MICROTRAC, available from MicrotracBEL Corp.].

[0181] The polymer compound (B) described above is a copolymer containing at least one monomer selected from the group consisting of acrylic acid and 2-ethylhexyl methacrylate as essential constituent monomers, and the total weight ratio of acrylic acid and 2-ethylhexyl methacrylate is 60% or more by weight based on the total weight of the constituent monomers of the copolymer.

[0182] Based on the total weight of the constituent monomers of the copolymer, when the total weight ratio of acrylic acid and 2-ethylhexyl methacrylate in the copolymer is less than 60% by weight, the cycling characteristics deteriorate.

[0183] The weight ratio of acrylic acid and 2-ethylhexyl methacrylate in the constituent monomers of the above copolymer can be measured by dissolving the copolymer in a supercritical fluid and analyzing the obtained oligomer components by gas chromatography-mass spectrometry (GC-MS).

[0184] The polymer compound (B) may contain constituent monomers other than acrylic acid and 2-ethylhexyl methacrylate.

[0185] Examples of constituent monomers other than acrylic acid and 2-ethylhexyl methacrylate include 2-methylhexyl acrylate, methyl methacrylate, etc.

[0186] Furthermore, it is preferred that the polymer compound (B) does not contain 1,6-hexanediol dimethacrylate as a constituent monomer.

[0187] The weight-average molecular weight of the polymer compound (B) described above [hereinafter abbreviated as Mw: measured based on gel permeation chromatography (GPC) as described later] is preferably 300,000 or less. If the Mw of the polymer compound (B) exceeds 300,000, the viscosity of the resin solution may increase too much, and a good coating may not be obtained.

[0188] The Mw of polymer compound (B) is more preferably 200,000 or less, and even more preferably 150,000 or less. The Mw of polymer compound (B) is preferably 40,000 or more, and more preferably 70,000 or more.

[0189] The measurement conditions for Mw by GPC are as follows.

[0190] Apparatus: High-temperature gel permeation chromatography [“Alliance GPC V2000”, available from Waters Corporation]; Solvent: o-dichlorobenzene

[0191] Standard material: polystyrene

[0192] Sample concentration: 3 mg / ml

[0193] Column solid phase: PLgel 10μm, MIXED-B, two columns in series (Polymer Laboratories Limited)

[0194] Column temperature: 135℃

[0195] The polymer compound (B) described above can be manufactured using known polymerization initiators {azo initiators [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylpentanonitrile, etc.)], peroxide initiators (benzoyl peroxide, di-tert-butyl peroxide, lauryl peroxide, etc.)} via known polymerization methods (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.).

[0196] From the viewpoint of adjusting Mw to a preferred range, the amount of polymerization initiator used, based on the total weight of monomers, is preferably 0.01% to 5% by weight, more preferably 0.05% to 2% by weight, and even more preferably 0.1% to 1.5% by weight. Although the polymerization temperature and polymerization time are adjusted according to the type of polymerization initiator, the polymerization temperature is preferably -5°C to 150°C (more preferably 30°C to 120°C), and the reaction time is preferably 0.1 hours to 50 hours (more preferably 2 hours to 24 hours).

[0197] Examples of solvents used in solution polymerization include esters (C2-C8, such as ethyl acetate and butyl acetate), alcohols (C1-C8, such as methanol, ethanol, and octanol), hydrocarbons (C4-C8, such as n-butane, cyclohexane, and toluene), and ketones (C3-C9, such as methyl ethyl ketone). From the viewpoint of adjusting the molecular weight to a preferred range, the amount used, based on the total weight of the monomers, is preferably 5% to 900% by weight, more preferably 10% to 400% by weight, and particularly preferably 30% to 300% by weight, and the monomer concentration is preferably 10% to 95% by weight, more preferably 20% to 90% by weight, and particularly preferably 30% to 80% by weight.

[0198] Examples of dispersion media in emulsion polymerization and suspension polymerization include water, alcohols (such as ethanol), esters (such as ethyl propionate), and light naphtha, while examples of emulsifiers include metal salts of higher fatty acids (C10-C24) (such as sodium oleate and sodium stearate), metal salts of sulfated esters of higher alcohols (C10-C24) (such as sodium dodecyl sulfate), ethoxylated tetramethyldecanediol, sodium ethyl methacrylate, and dimethylaminomethyl methacrylate. Furthermore, polyvinyl alcohol and polyvinylpyrrolidone can be added as stabilizers.

[0199] In solution polymerization, the monomer concentration in the solution, and in emulsion polymerization and suspension polymerization, the monomer concentration in the dispersion is preferably 5% to 95% by weight, more preferably 10% to 90% by weight, and still more preferably 15% to 85% by weight. Based on the total weight of the monomers, the amount of polymerization initiator used is preferably 0.01% to 5% by weight, more preferably 0.05% to 2% by weight.

[0200] For polymerization, known chain transfer agents can be used, such as mercapto compounds (dodecyl mercaptan, n-butyl mercaptan, etc.) and / or halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.).

[0201] In the coated negative electrode active material particles, at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing a polymer compound (B). If necessary, the coating layer may further contain a conductive material.

[0202] The weight ratio of the polymer compound (B) relative to the weight of the negative electrode active material particles is not particularly limited, but from the viewpoint of fixing the position of the coated negative electrode active material particles and from the viewpoint of the formability of the negative electrode composition layer, it is preferably 0.1% to 10% by weight.

[0203] For example, the above-mentioned coated negative electrode active material particles can be obtained as follows: while stirring the above-mentioned negative electrode active material particles at 30 rpm to 50 rpm in a general mixer, a resin solution containing the above-mentioned polymer compound (B) is added dropwise over 1 minute to 90 minutes; a conductive additive is further added as needed; while stirring the mixture, the temperature is raised to 50°C to 200°C and the pressure is reduced to 0.007 MPa to 0.04 MPa; and the mixture is then kept in this state for 10 minutes to 150 minutes.

[0204] The aforementioned negative electrode composition layer contains a conductive additive. As the aforementioned conductive additive, the same conductive additive contained in the aforementioned resin current collector can be appropriately used.

[0205] From the viewpoint of electrical characteristics, the weight percentage of conductive additives contained in the negative electrode composition layer is preferably 0.1% to 10% by weight, based on the weight of the negative electrode composition layer.

[0206] The aforementioned conductive additive may be contained in a coating layer covering the negative electrode active material particles, or it may be contained in a layer other than the aforementioned coating layer.

[0207] There is no particular limitation on the thickness of the above-mentioned negative electrode composition layer, but from the viewpoint of energy density, it is preferably 110 μm to 900 μm.

[0208] In the negative electrode used in lithium-ion batteries, the current collector and the negative electrode composition layer do not adhere to each other. Therefore, even if the volume of the negative electrode composition layer changes due to charging and discharging, the current collector will not change accordingly, and thus self-destruction of the negative electrode composition layer and irreversible peeling of the current collector are impossible.

[0209] The fact that the current collector and the negative electrode composition layer do not adhere to each other means that the adhesive strength between the current collector and the negative electrode composition layer is 20 N or less. The adhesive strength between the current collector and the negative electrode composition layer can be measured using the JIS K6850:1999 adhesive strength test. The measurement conditions are as follows.

[0210] Test environment: 25℃, 50% humidity

[0211] Measuring device: Shimadzu AUTOGRAPH AGS-10kNX

[0212] Measurement conditions: As the test specimen, a current collector was used instead of a JIS-standard metal plate. To reproduce the internal environment of the battery cell, measurements were taken at 1 kgf / cm² on the adhesive surface of the current collector and negative electrode composition layer. 2 Measurements were taken under load.

[0213] [Method for Manufacturing a Negative Electrode for a Lithium-ion Battery] A method for manufacturing a negative electrode for a lithium-ion battery is a method for manufacturing a negative electrode for a lithium-ion battery, the negative electrode for the lithium-ion battery comprising a current collector and a negative electrode composition layer disposed on the surface of the current collector, the method comprising the steps of: preparing a negative electrode composition layer by compression molding of a negative electrode composition containing coated negative electrode active material particles and conductive additives, wherein at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing a polymer compound (B); and repositioning the negative electrode composition layer on the current collector, the polymer compound (B) being a copolymer containing at least one monomer selected from the group consisting of acrylic acid and 2-ethylhexyl methacrylate as essential constituent monomers; and based on the total weight of the constituent monomers of the copolymer, the total weight ratio of acrylic acid and 2-ethylhexyl methacrylate is 60% or greater by weight.

[0214] A method for manufacturing a negative electrode for a lithium-ion battery includes the step of preparing a negative electrode composition layer by compressing a negative electrode composition containing coated negative electrode active material particles and a conductive additive, wherein at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing a polymer compound (B).

[0215] Compression molding can be performed using any pressurizing device and pressurizing fixture, such as a hydraulic device. For example, the negative electrode composition is loaded into a cylindrical bottom container, a cylindrical rod-shaped pressurizing fixture with a diameter slightly smaller than the inner diameter of the bottom container is inserted from above, and then compressed by the pressurizing device, thereby obtaining a layer of negative electrode composition as a cylindrical molded body.

[0216] By changing the shape of the pressure fixture, molded bodies of any shape can be obtained.

[0217] As the compression condition in compression molding, the pressure applied to the negative electrode composition is preferably from 100 MPa to 3000 MPa. The pressurization time is preferably from 1 second to 300 seconds.

[0218] The compression molding steps described above can be performed on the current collector or on a release material other than the current collector. There are no particular limitations on the release material, and known release papers or release films can be appropriately selected and used.

[0219] Examples of release materials include release papers such as cellophane, kraft paper, and clay-coated paper, and release films made from non-fluorinated resins such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene, and polyimide (PI), or from fluorinated resins such as polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-hexafluoropropylene copolymer, perfluoroalkoxyalkane (PFA), and polyvinylidene fluoride (PVdF).

[0220] A method for manufacturing a negative electrode for a lithium-ion battery includes a step of repositioning the negative electrode composition layer obtained in the compression molding step described above onto a current collector.

[0221] There are no particular limitations on the method for repositioning the negative electrode composition layer onto the current collector, and known transfer methods can be used. For example, a negative electrode for lithium-ion batteries can be obtained by laminating the negative electrode composition layer formed on a release material in a compression molding step onto the current collector and peeling off the release material.

[0222] Example

[0223] Subsequently, specific examples will be described regarding the negative electrode for lithium-ion batteries and the manufacturing method for the negative electrode for lithium-ion batteries; however, without departing from the spirit of the above-described manufacturing method for the negative electrode for lithium-ion batteries, the manufacturing method for the negative electrode for lithium-ion batteries is not limited to the following examples. Unless otherwise stated, parts refer to parts by weight, and % refers to percentage by weight.

[0224] <Manufacturing Example 2-1: Manufacturing of Polymer Compound (B-1)>

[0225] 66.46 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the temperature was raised to 75°C. Then, while blowing nitrogen into the flask, a monomer blend solution obtained by blending 10.0 parts of methacrylic acid, 90.0 parts of 2-ethylhexyl methacrylate, and 116.5 parts of DMF, along with an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF, was continuously added dropwise over 2 hours using a dropping funnel to carry out free radical polymerization. After the addition was complete, the reaction was continued at 75°C for 3 hours. Then, the temperature was raised to 80°C, and again, while stirring, an initiator solution obtained by dissolving 1.7 parts of 2,2'-azobis(2,4-dimethylpentanonitrile) in 29.15 parts of DMF was continuously added dropwise over 2 hours using a dropping funnel. After dropwise addition, the reaction continued for 3 hours to obtain a copolymer compound (B-1) for coating with a resin concentration of 30%.

[0226] <Manufacturing Examples 2-2 to 2-8: Manufacturing of Polymer Compounds (B-2) to (B-5) and (B'-1) to (B'-3)>

[0227] Solutions of polymer compounds (B-2) to (B-5) and (B'-1) to (B'-3) were prepared in the same manner as in manufacturing example 2-1, except that the monomers placed were changed according to Table 2-1.

[0228] [Table 2-1]

[0229]

[0230] <Manufacturing Example 2-9: Manufacturing of Coated Negative Electrode Active Material Particles (DB-1)>

[0231] 87 parts of negative electrode active material powder (D-1) (hard carbon available from JFE Chemical Corporation) were placed in a general-purpose mixer, a high-speed mixer FS25 [manufactured by Alstec Corporation], and while stirring the powder at room temperature and 720 rpm, 20.2 parts of the coating polymer compound solution (B-1) obtained in Manufacturing Example 2-1 were added dropwise over 2 minutes, and the resulting mixture was then stirred for another 5 minutes.

[0232] Next, while the mixture was stirred, 6.0 parts of acetylene black [DENKA BLACK (registered trademark) manufactured by Denka Company Limited] were added in portions over 26 minutes as a conductive additive, and stirring was continued for 30 minutes. Then, while maintaining stirring, the pressure was reduced to 0.01 MPa, and then the temperature was increased to 140°C while maintaining stirring and pressure reduction. The stirring, pressure reduction, and temperature were maintained for 8 hours to distill off volatile substances. The resulting powder was graded using a 212 μm sieve to obtain coated negative electrode active material particles (DB-1).

[0233] <Manufacturing Examples 2-10 to 2-16: Manufacturing of Coated Negative Electrode Active Material Particles (DB-2) to (DB-5), (DB'-1) to (DB'-3)>

[0234] Except for changing the polymer compound solution (B-1) used for coating to (B-2) to (B-5) and (B'-1) to (B'-3), coated negative electrode active material particles (DB-2) to (DB-5) and (DB'-1) to (DB'-3) are obtained in the same manner as in manufacturing examples 2-9. Detailed combinations are shown in Table 2-2.

[0235] <Manufacturing Example 2-17: Manufacturing of Electrolyte Solutions>

[0236] LiPF6 was dissolved in a mixed solvent of ethylene carbonate and propylene carbonate (volume ratio 1:1) at a ratio of 1 mol / L to obtain an electrolyte solution for lithium-ion batteries.

[0237] <Manufacturing Example 2-18: Manufacturing of Current Collectors>

[0238] In a twin-screw extruder, 10 parts of the product “SunAllomer PB522M” [available from SunAllomer Ltd.], 25 parts of the product “SunAllomer PM854X” [available from SunAllomer Ltd.], 10 parts of the product “Suntec B680” [available from Asahi Kasei Chemicals Corporation], 40 parts of graphite granules “SNG-WXA1”, 10 parts of acetylene black 1 “Ensaco 250G”, and 5 parts of the product “Youmex 1001 (acid-modified polypropylene)” [available from Sanyo Chemical Industries, Ltd.] were melt-kneaded at 180°C and 100 rpm for a residence time of 5 minutes to obtain a material for resin current collectors.

[0239] The obtained material for the resin current collector is passed through a T-die extruder and then rolled by a hot press with the temperature controlled at 50°C to obtain the resin current collector.

[0240] <Example 2-1>

[0241] 5g of coated negative electrode active material particles (DB-1) obtained in Manufacturing Examples 2-9, 0.0505g of carbon fiber [Donna Carbo Milled S-242, available from Osaka Gas Chemicals Co., Ltd.] as a conductive additive, and 0.2632g of flake graphite [UP-5-α, available from Nippon Graphite Co., Ltd.] were mixed at 1,500 rpm for 3 minutes using a planetary stirring type mixing and kneading apparatus {Awatori Rentaro [THINKY Corporation]}.

[0242] In addition, after adding 0.14 g of the electrolyte solution prepared in Manufacturing Example 2-17, the mixture was mixed with Awatori Rentaro at 1,500 rpm for 1 minute, mixed twice, and a total of 0.28 g of electrolyte solution was added to obtain the negative electrode composition.

[0243] Weigh 0.055g of the above negative electrode composition and place it in a cylindrical bottom container with an inner diameter of 15mm. Then compress it with a pressure device to obtain a cylindrical negative electrode composition layer (DE-1).

[0244] The pressurization conditions are a pressurization pressure of 150 MPa and a pressurization time of 5 seconds, and the temperature of the pressurization device (pressurization clamp) is 180°C, which is equal to the room temperature during pressurization.

[0245] <Examples 2-2 to 2-5, Comparison Examples 2-1 to 2-3>

[0246] Except that the coated negative electrode active material particles (DB-1) are changed to coated negative electrode active material particles (DB-2) to (DB-5), (DB'-1) to (DB'-3), the negative electrode composition layers (DE-2) to (DE-5), (DE'-1) to (DE'-3) are prepared in the same manner as in Example 2-1. Detailed combinations are shown in Table 2-2.

[0247] <Evaluation of Cyclic Characteristics>

[0248] PP sheets (available from AS ONE) cut into 2cm squares were prepared, with a φ18mm hole in the center. The prepared negative electrode composition layer (DE-1) and a φ15mm Li foil were stored in the φ18mm hole in the center of the PP sheet, with the layer and foil positioned at the electrode end of a PP separator (available from Celgard, LLC). 110% (v / v) of electrolyte solution was injected relative to the gap between the negative electrode composition layer (DE-1) and the separator. The resin current collector obtained in Manufacturing Examples 2-11 and a 2cm square copper foil were placed on the outer sides of the negative electrode composition layer (DE-1) and the Li foil, respectively. The cells were then heat-sealed under reduced pressure to prepare an evaluation battery.

[0249] The evaluation battery was connected to a charge / discharge device, and its cycle characteristics were evaluated under the following conditions.

[0250] Under CC-CV (cutoff current 0.01C), the capacitor was charged to 0V at 0.1C and then discharged to 1.5V at 0.01C after a 1-hour pause. This discharge capacity was set as the initial capacity X0. This process was repeated 30 times to obtain the capacity X1 of the 30th cycle. The cycle characteristics were evaluated using X1 / X0 as the discharge capacity retention rate after 30 cycles. The evaluation was performed under the following criteria. The results are described in Table 2-2.

[0251] ◎: Discharge capacity retention rate of 80% or greater

[0252] ○: Discharge capacity retention is 70% or greater, but less than 80%.

[0253] Δ: Discharge capacity retention is 40% or greater, but less than 70%.

[0254] ×: Discharge capacity retention is less than 40%.

[0255] [Table 2-2]

[0256]

[0257] The results in Table 2-2 show that lithium-ion batteries manufactured using the negative electrode for lithium-ion batteries exhibit excellent cycle characteristics.

[0258] This specification describes the following technical ideas as described in the basic application of this international application.

[0259] (1-1) A positive electrode for a lithium-ion battery, comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector.

[0260] The current collector and the positive electrode composition layer do not adhere to each other.

[0261] The positive electrode composition layer contains coated positive electrode active material particles and conductive additives, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing polymer compound (A).

[0262] The polymer compound (A) is any one of the following:

[0263] A copolymer (A1) comprising methacrylic acid, lauryl methacrylate, and 1,6-hexanediol dimethacrylate as monomers.

[0264] A copolymer (A2) containing isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers, or

[0265] A copolymer (A3) comprising lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as monomers.

[0266] Based on the total weight of the monomers constituting the copolymer, the weight percentage of 1,6-hexanediol dimethacrylate contained in the monomers of the copolymer is 0.2% to 1% by weight, and

[0267] The polymer compound (A) has a weight-average molecular weight of 300,000 or less.

[0268] (1-2) The positive electrode for a lithium-ion battery according to (1-1), wherein the thickness of the positive electrode composition layer is 100 μm to 800 μm.

[0269] (1-3) A method for manufacturing a positive electrode for a lithium-ion battery, the positive electrode comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector, the method comprising the following steps:

[0270] A positive electrode composition layer is prepared by compression molding of a positive electrode composition containing coated positive electrode active material particles and a conductive additive, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A); and

[0271] The positive electrode composition layer is repositioned on the current collector.

[0272] The polymer compound (A) is any one of the following:

[0273] A copolymer (A1) having methacrylic acid, lauryl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers;

[0274] A copolymer containing isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A2); or

[0275] A copolymer (A3) comprising lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as monomers.

[0276] Based on the total weight of the monomers constituting the copolymer, the weight percentage of 1,6-hexanediol dimethacrylate contained in the monomers of the copolymer is 0.2% to 1% by weight, and

[0277] The polymer compound (A) has a weight-average molecular weight of 300,000 or less.

[0278] (2-1) A negative electrode for a lithium-ion battery, having a current collector and a negative electrode composition layer disposed on the surface of the current collector,

[0279] The current collector and the negative electrode composition layer do not adhere to each other;

[0280] The negative electrode composition layer contains coated negative electrode active material particles and conductive additives, wherein at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing polymer compound (A).

[0281] The polymer compound (B) is a copolymer containing at least one monomer selected from the group consisting of acrylic acid and 2-ethylhexyl methacrylate as essential constituent monomers; and the total weight ratio of acrylic acid and 2-ethylhexyl methacrylate is 60% or more by weight, based on the total weight of the constituent monomers of the copolymer.

[0282] (2-2) The negative electrode for a lithium-ion battery according to (2-1), wherein the thickness of the negative electrode composition layer is 100 μm to 900 μm.

[0283] (2-3) A method for manufacturing a negative electrode for a lithium-ion battery, the negative electrode comprising a current collector and a negative electrode composition layer disposed on the surface of the current collector, the method comprising the following steps:

[0284] A negative electrode composition layer is prepared by compression molding of a negative electrode composition containing coated negative electrode active material particles and a conductive additive, wherein at least a portion of the surface of each negative electrode active material particle is coated with a coating layer containing a polymer compound (A); and

[0285] The negative electrode composition layer is repositioned on the current collector.

[0286] The polymer compound (A) is a copolymer containing at least one monomer selected from the group consisting of acrylic acid and 2-ethylhexyl methacrylate as essential constituent monomers; and

[0287] Based on the total weight of the constituent monomers of the copolymer, the total weight ratio of acrylic acid and 2-ethylhexyl methacrylate is 60% or more by weight.

[0288] The polymer compound (A) in (2-1), (2-2) and (2-3) above refers to the polymer compound (B) in this specification.

[0289] practicality

[0290] The positive electrode of the present invention for lithium-ion batteries can be particularly used as the positive electrode for lithium-ion batteries in mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims

1. A positive electrode for a lithium-ion battery, comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector, The current collector and the positive electrode composition layer do not adhere to each other. The positive electrode composition layer contains coated positive electrode active material particles and conductive additives, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing polymer compound (A). The polymer compound (A) is any one of the following: A copolymer (A1) comprising methacrylic acid, lauryl methacrylate, and 1,6-hexanediol dimethacrylate as monomers. A copolymer (A2) containing isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers, or A copolymer (A3) comprising lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as monomers. Based on the total weight of the monomers constituting the copolymer, the weight percentage of 1,6-hexanediol dimethacrylate contained in the monomers of the copolymer is 0.2% to 1% by weight, and The polymer compound (A) has a weight-average molecular weight of 300,000 or less.

2. The positive electrode for a lithium-ion battery according to claim 1, wherein, The thickness of the positive electrode composition layer is 100 to 800 μm.

3. A method for manufacturing a positive electrode for a lithium-ion battery, the positive electrode comprising a current collector and a positive electrode composition layer disposed on the surface of the current collector, the method comprising the following steps: A positive electrode composition layer is prepared by compression molding of a positive electrode composition containing coated positive electrode active material particles and a conductive additive, wherein at least a portion of the surface of each positive electrode active material particle is coated with a coating layer containing a polymer compound (A); and The positive electrode composition layer is repositioned on the current collector. The polymer compound (A) is any one of the following: A copolymer (A1) having methacrylic acid, lauryl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers; A copolymer containing isobornyl methacrylate and 1,6-hexanediol dimethacrylate as constituent monomers (A2); or A copolymer (A3) comprising lauryl methacrylate, 2-ethylhexyl methacrylate and 1,6-hexanediol dimethacrylate as monomers. Based on the total weight of the monomers constituting the copolymer, the weight percentage of 1,6-hexanediol dimethacrylate contained in the monomers of the copolymer is 0.2% to 1% by weight, and The polymer compound (A) has a weight-average molecular weight of 300,000 or less.

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