Coated electrode active material particles for lithium ion battery, electrode for lithium ion battery, lithium ion cell, and battery module

Abstract

To provide coated electrode active material particles for a lithium ion battery, which enable the production of electrodes having excellent moldability (low defect rate) and a smooth surface.SOLUTION: Coated electrode active material particles for a lithium ion battery are formed by coating at least a portion of the surface of the electrode active material particles with a coating layer containing a polymer compound and a conductive assistant, and the coated electrode active material particles for the lithium ion battery have a Carr fluidity index of 55 to 65.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to coated electrode active material particles for lithium ion batteries, electrodes for lithium ion batteries, lithium ion single cells, and battery modules.

Background Art

[0002] Lithium ion batteries with high energy density are known as batteries that can be used as power sources for electric vehicles, hybrid electric vehicles, etc., and stationary power sources, etc. A lithium ion battery accommodates a power storage element in which single cells are connected in series in a battery exterior container, and is used as a power source in the form of a battery module adjusted to a required voltage, or a battery pack in which a plurality of battery modules are combined to adjust the voltage and capacity.

[0003] When there is a difference in capacity between a plurality of single cells, control is performed to stop discharging in accordance with the single cell having a small capacity in order to avoid over-discharge during discharge. Further, control is performed to stop charging in accordance with the single cell that first becomes fully charged in order to avoid over-charging during charging due to the difference in remaining capacity at the end of discharge. For this reason, the available capacity becomes less than the sum of the capacities of the plurality of single cells. One of the factors causing variations in the capacity of single cells is that the handleability of the electrode active material particles is poor, and the amount of electrode active material particles supplied to the electrode varies. Further, as a result of variations in the amount of electrode active material particles, when the electrode surface becomes uneven, the battery performance also deteriorates when single cells are stacked.

[0004] When there are irregularities in the thickness of the electrode or the electrode surface is not smooth, in order to minimize the adverse effects on a battery module in which single cells are stacked, for example, it has been proposed to install a conductive elastic member in the battery module (see Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the method described in Patent Document 1 could not solve the problem that the capacity of the single cells constituting the battery could not be effectively utilized.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide coated electrode active material particles for a lithium-ion battery that are excellent in moldability (low defect rate) and have a smooth surface.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have reached the present invention. That is, the present invention is coated electrode active material particles for a lithium-ion battery in which at least a part of the surface of the electrode active material particles is coated with a coating layer containing a polymer compound and a conductive assistant, and the Carr flowability index is 55 to 65. Coated electrode active material particles for a lithium-ion battery characterized by being; a lithium-ion battery electrode provided with the above coated electrode active material particles for a lithium-ion battery; a lithium-ion single cell provided with the above lithium-ion battery electrode; It relates to a battery module in which a plurality of the above lithium-ion single cells are stacked.

Effects of the Invention

[0009] According to the present invention, it is possible to provide coated electrode active material particles for a lithium-ion battery that are excellent in moldability (low defect rate) and have a smooth surface.

Modes for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in detail. The present invention relates to coated electrode active material particles for a lithium-ion battery, a lithium-ion battery electrode, a lithium-ion single cell, and a battery module. In addition, in this specification, when referring to a lithium-ion battery, it is to be understood as including the concept of a lithium-ion secondary battery.

[0011] [Coated Electrode Active Material Particles for Lithium-Ion Batteries] The coated electrode active material particles for lithium-ion batteries of the present invention are coated electrode active material particles for lithium-ion batteries in which at least a part of the surface of the electrode active material particles is coated with a coating layer containing a polymer compound and a conductive assistant, and are characterized in that the Carr's flowability index is 55 to 65.

[0012] The coated electrode active material particles for lithium-ion batteries of the present invention have a Carr's flowability index of 55 to 65. The Carr's flowability index is obtained by measuring the angle of repose, compressibility, spatula angle, and uniformity or degree of aggregation of the coated electrode active material particles for lithium-ion batteries, determining the index for each item with reference to Table 2 of "Powder Technology Pocket Book" written by Tsuneomi Hayashi (published by Kogyo Chosa Kai, Inc., 1996), and taking the total value.

[0013] The angle of repose (°), compressibility (%), spatula angle (°), and uniformity (-) of the coated electrode active material particles for lithium-ion batteries can be measured using a multifunctional powder physical property measuring instrument (Seishin Enterprise Co., Ltd., Multi Tester MT-02). The temperature during measurement is 25°C and the humidity is 50%. By referring to Table 2 of the "Powder Technology Pocket Book", the index corresponding to each measured value can be obtained. By summing up the indices of each measured value, the Carr's flowability index can be obtained.

[0014] When the Carr's flowability index of the coated electrode active material particles for lithium-ion batteries is 55 to 65, electrodes with excellent formability (low defect rate) and smooth surfaces can be obtained. By using electrodes with excellent formability (low defect rate) and smooth surfaces, the discharge capacity retention rate in lithium-ion single cells and battery modules can be improved.

[0015] When the Carr fluidity index is less than 55, the handleability of the coated electrode active material particles for lithium-ion batteries is poor. Therefore, when forming the electrode, the amount of the coated electrode active material particles for lithium-ion batteries is not uniformly supplied, and the amount of the coated electrode active material particles for lithium-ion batteries varies from place to place. When the amount of the coated electrode active material particles for lithium-ion batteries varies, the surface roughness of the electrode surface increases. When the surface roughness of the electrode surface increases, the discharge capacity retention rate in the lithium-ion single cell and the battery module decreases.

[0016] When the Carr fluidity index is greater than 65, the strength of the electrode decreases. Therefore, the defect rate when cutting out the electrode increases, and the formability of the electrode deteriorates. When the formability of the electrode deteriorates, the discharge capacity retention rate in the lithium-ion single cell and the battery module decreases.

[0017] The Carr fluidity index is preferably 55 to 60. When the Carr fluidity index is 55 to 60, an electrode with better formability (lower defect rate) can be obtained.

[0018] For example, the Carr fluidity index can be adjusted by adjusting the mesh opening of the sieve used when classifying the coated electrode active material particles for lithium-ion batteries, or by adjusting the content ratios of the electrode active material particles, the polymer compound, and the conductive assistant in the coated electrode active material particles for lithium-ion batteries.

[0019] When the coated electrode active material particles for lithium-ion batteries contain a liquid component such as the electrolyte contained in the electrode, after removing the liquid component from the coated electrode active material particles for lithium-ion batteries by vaporizing the liquid component or the like, the Carr fluidity index is measured. Also, for each parameter of the coated electrode active material particles for lithium-ion batteries described below, each parameter is measured after removing the liquid component. The moisture content of the coated electrode active material particles for lithium-ion batteries can be measured by the infrared moisture meter method.

[0020] The coated electrode active material particles for lithium-ion batteries preferably have an internal friction angle of 38.9° or more. The internal friction angle represents the mutual friction between the constituent powders and the resistance of meshing in terms of an angle, and is a parameter representing the ease of slipping of the powders. The internal friction angle can be measured, for example, by a commercially available powder layer shear force measuring device.

[0021] The smaller the internal friction angle, the easier the powder slips and the higher the fluidity. If the fluidity becomes too high, there is a risk of separation between the other electrode composition and the coated electrode active material particles for lithium-ion batteries. Therefore, in order to particularly suppress separation, the coated electrode active material particles for lithium-ion batteries preferably have an internal friction angle of 38.9° or more. The coated electrode active material particles for lithium-ion batteries more preferably have an internal friction angle of 39.1° or more.

[0022] The coated electrode active material particles for lithium-ion batteries preferably have a shear adhesion force of 620 Pa or more for a powder layer composed of the coated electrode active material particles for lithium-ion batteries at a vertical pressure of 20 kPa in a shear test based on JIS-Z8835. The shear adhesion force at a vertical pressure of 20 kPa means the shear adhesion force measured with a pre-compression stress of 20 kPa in JIS-Z8835.

[0023] The shear adhesion force of the powder layer can be measured by the rotational cell constant volume method using a shear type powder fluidity measuring machine (Volution Powder Tester, manufactured by Mercury Scientific) based on JIS-Z8835 (Method for measuring the critical state line (CSL) and wall collapse line (WYL) by one-sided shear test). The collapse behavior of a powder layer composed of the coated electrode active material particles for lithium-ion batteries at a vertical pressure of 20 kPa can be measured, and the shear adhesion force of the powder layer at a vertical pressure of 20 kPa can be determined.

[0024] The shear adhesion force of the powder layer composed of coated electrode active material particles for lithium-ion batteries indicates the adhesion between the powders (coated electrode active material particles for lithium-ion batteries) when the powder layer is compressed under a pressure of 20 kPa. A large shear adhesion force of the powder layer means strong adhesion under pressure. From the perspective of reducing the defect rate of the electrode, the shear adhesion force of the powder layer composed of coated electrode active material particles for lithium-ion batteries is preferably 620 Pa or more, and more preferably 680 Pa or more.

[0025] The coated electrode active material particles for lithium-ion batteries preferably have an average envelope area of 30 μm 2 or less, and / or an average envelope perimeter of 20 μm or less. The envelope area of the coated electrode active material particles for lithium-ion batteries refers to the area of the surface surrounded by a line connecting the vertices of the convex portions of the particle cross-section (the length of this line is referred to as the envelope perimeter).

[0026] The average envelope area and the average envelope perimeter can be determined by image analysis of the projection image of the coated electrode active material particles for lithium-ion batteries. In the present invention, they can be measured as follows. Using a particle size and shape distribution measuring instrument (PITA-1 manufactured by Seishin Enterprise Co., Ltd.), 3000 coated electrode active material particles for lithium-ion batteries are observed, and the envelope perimeter and the envelope area are measured using the software (ImageAnalysis) attached to the apparatus to obtain the average envelope perimeter and the average envelope area. At this time, propylene carbonate is used as the dispersion medium. A sample solution prepared by dispersing 0.1 g of the coated electrode active material particles for lithium-ion batteries in propylene carbonate is used.

[0027] The coated electrode active material particles for lithium-ion batteries preferably have an average envelope area of 30 μm 2 or less. Also, the coated electrode active material particles for lithium-ion batteries preferably have an average envelope perimeter of 20 μm or less. The coated electrode active material particles for lithium-ion batteries preferably have an average envelope area of 30 μm 2 or less and an average envelope perimeter of 20 μm or less.

[0028] The volume average particle diameter of the coated electrode active material particles for a lithium ion battery is preferably from 0.01 to 100 μm, more preferably from 5 to 40 μm. It is difficult to produce coated electrode active material particles for a lithium ion battery having a volume average particle diameter of less than 5 μm. When the volume average particle diameter of the coated electrode active material particles for a lithium ion battery exceeds 40 μm, it becomes difficult to form the electrode active material layer.

[0029] In the present specification, the volume average particle diameter means the particle diameter (Dv50) at the integrated value of 50% in the particle size distribution determined by the Microtrac method (laser diffraction / scattering method). The Microtrac method is a method for obtaining a particle size distribution by using scattered light obtained by irradiating particles with laser light. For measuring the volume average particle diameter of particles, Microtrac manufactured by Nikkiso Co., Ltd. or the like can be used.

[0030] Hereinafter, each component of the coated electrode active material particles for a lithium ion battery of the present invention will be described in detail.

[0031] (Electrode active material particles) In the coated electrode active material particles for a lithium ion battery of the present invention, the electrode active material particles may be positive electrode active material particles or negative electrode active material particles. When the electrode active material particles are positive electrode active material particles, the coated electrode active material particles for a lithium ion battery of the present invention are used for producing a positive electrode. When the electrode active material particles are positive electrode active material particles, the coated electrode active material particles for a lithium ion battery become coated positive electrode active material particles. Also, when the electrode active material particles are negative electrode active material particles, the coated electrode active material particles for a lithium ion battery of the present invention are used for producing a negative electrode. When the electrode active material particles are negative electrode active material particles, the coated electrode active material particles for a lithium ion battery become coated negative electrode active material particles.

[0032] When the electrode active material particles are positive electrode active material particles, the positive electrode active material particles are composite oxides of lithium and transition metals {composite oxides with one type of transition metal (such as LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, and LiMn2O4, etc.), composite oxides with two types of transition metal elements (for example, LiFeMnO4, LiNi 1-x Co x O2, 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) and composite oxides with three or more types of transition metal elements [for example, LiM a M’ b M’’ c O2 (M, M’, and M’’ are different transition metal elements respectively, and satisfy a + b + c = 1. For example, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2), etc.] etc., lithium-containing transition metal phosphates (such as LiFePO4, LiCoPO4, LiMnPO4, and LiNiPO4), transition metal oxides (such as MnO2 and V2O5), transition metal sulfides (such as MoS2 and TiS2), and conductive polymers (such as polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyvinyl carbazole), etc. may be mentioned, and two or more types may be used in combination. In addition, the lithium-containing transition metal phosphate may be one in which a part of the transition metal site is substituted with another transition metal.

[0033] From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the positive electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 35 μm, and still more preferably 2 to 30 μm.

[0034] When the electrode active material particles are negative electrode active material particles, the negative electrode active material particles are carbon-based materials [graphite (graphite), non-graphitizable carbon (hard carbon), amorphous carbon, resin fired bodies (such as those obtained by firing and carbonizing phenol resins and furan resins, etc.), cokes (such as pitch coke, needle coke, and petroleum coke, etc.) and carbon fibers, etc.], silicon-based materials [silicon, silicon oxide (SiO x ), silicon-carbon composites (those obtained by coating the surface of carbon particles with silicon and / or silicon carbide, those obtained by coating the surface of silicon particles or silicon oxide particles with carbon and / or silicon carbide, and silicon carbide, etc.), and silicon alloys (such as silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon-titanium alloy, silicon-manganese alloy, silicon-copper alloy, and silicon-tin alloy, etc.) etc.], conductive polymers (such as polyacetylene and polypyrrole, etc.), metals (such as tin, aluminum, zirconium, and titanium, etc.), metal oxides (such as titanium oxide and lithium titanate, etc.), and metal alloys (such as lithium-tin alloy, lithium-aluminum alloy, and lithium-aluminum-manganese alloy, etc.) etc. and mixtures of these with carbon-based materials, etc. can be mentioned. Among the above negative electrode active material particles, for those that do not contain lithium or lithium ions inside, a pre-doping treatment may be performed to make a part or all of the negative electrode active material particles contain lithium or lithium ions in advance.

[0035] From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the negative electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 60 μm, and still more preferably 2 to 40 μm.

[0036] (Coating layer) In the coated electrode active material particles for a lithium ion battery of the present invention, the coating layer contains a polymer compound and a conductive assistant.

[0037] (Polymer compound) As the high molecular compound, a (meth)acrylic polymer having at least two kinds of (meth)acrylic acid alkyl ester monomers having a branched alkyl group and a carboxylic acid-containing vinyl compound as essential constituent units is preferable.

[0038] ((meth)acrylic acid alkyl ester monomer having a branched alkyl group) Examples of the (meth)acrylic acid alkyl ester monomer having a branched alkyl group include monomers represented by the following general formula (1). CH2=C(R 1 )COOR 2 (1) [In formula (1), R 1 is a hydrogen atom or a methyl group, and R 2 is a branched alkyl group having 4 to 36 carbon atoms.]

[0039] As the branched alkyl group having 4 to 36 carbon atoms, 1-methylpropyl group (sec-butyl group), 2-methylpropyl group, 1,1-dimethylethyl group (tert-butyl group), isobutyl group, 1-methylbutyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group (neopentyl group), 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, 1-methylhexyl group, 2-methylhexyl group, 3-methylhexyl group, 4-methylhexyl group, 5-methylhexyl group, 1-ethylpentyl group, 2-ethylpentyl group, 3-ethylpentyl group, 1,1-dimethylpentyl group, 1,2-dimethylpentyl group, 1,3-dimethylpentyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2-ethylpentyl group, 1-methylheptyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methylheptyl group, 5-methylheptyl group, 6-methylheptyl group, 1,1-dimethylhexyl group, 1,2-dimethylhexyl group, 1,3-dimethylhexyl group, 1,4-dimethylhexyl group, 1,5-dimethylhexyl group, 1-ethylhexyl group, 2-ethylhexyl group, 1-methyloctyl group, 2-methyloctyl group, 3-methyloctyl group, 4-methyloctyl group, 5-methyloctyl group, 6-methyloctyl group, 7-methyloctyl group (isononyl group), 1,1-dimethylheptyl group, 1,2-dimethylheptyl group, 1,3-dimethylheptyl group, 1,4-dimethylheptyl group, 1,5-dimethylheptyl group, 1,6-dimethylheptyl group, 1-ethylheptyl group, 2-ethylheptyl group, 1-methylnonyl group, 2-methylnonyl group, 3-methylnonyl group, 4-methylnonyl group, 5-methylnonyl group, 6-methylnonyl group, 7-methylnonyl group, 8-methylnonyl group (isodecyl group), 1,1-dimethyloctyl group, 1,2-dimethyloctyl group, 1,3-dimethyloctyl group, 1,4-dimethyloctyl group, 1,5-dimethyloctyl group, 1,6-dimethyloctyl group, 1,7-dimethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 1-methyldecyl group, 2-methyldecyl group, 3-methyldecyl group, 4-methyldecyl group, 5-methyldecyl group, 6-methyldecyl group, 7-methyldecyl group, 8-methyldecyl group, 9-methyldecyl group, 1,1-dimethylnonyl group, 1,2-dimethylnonyl group, 1,3-dimethylnonyl group, 1,4-dimethylnonyl group, 1,5-dimethylnonyl group, 1,6-dimethylnonyl group, 1,7-dimethylnonyl group, 1,8-dimethylnonyl group, 1-ethylnonyl group, 2-ethylnonyl group, 1-methylundecyl group, 2-methylundecyl group, 3-methylundecyl group, 4-methylundecyl group, 5-methylundecyl group, 6-methylundecyl group, 7-methylundecyl group, 8-methylundecyl group, 9-methylundecyl group, 10-methylundecyl group, 1,1-dimethyldecyl group, 1,2-dimethyldecyl group, 1,3-dimethyldecyl group, 1,4-dimethyldecyl group, 1,5-dimethyldecyl group, 1,6-dimethyldecyl group, 1,7-dimethyldecyl group, 1,8-dimethyldecyl group, 1,9-dimethyldecyl group, 1-ethyldecyl group, 2-ethyldecyl group, 1-methyldodecyl group, 1-butyleicosyl group, 1-hexyloctadecyl group, 1-octylhexadecyl group, 1-decyltetradecyl group, 1-undecyltridecyl group, etc., 2-methyldodecyl group, 2-hexyloctadecyl group, 2-octylhexadecyl group, 2-decyltetradecyl group, 2-undecyltridecyl group, 2-dodecylhexadecyl group, 2-tridecylpentadecyl group, 2-decyloctadecyl group, 2-tetradecyloctadecyl group, 2-hexadecyloctadecyl group, 2-tetradecyleicosyl group, 2-hexadecyloicosyl group, etc., and one or more branched alkyl groups such as residues obtained by removing a hydroxyl group from oxo alcohols obtained from propylene oligomers (7 to 11 mers), ethylene / propylene (molar ratio 16 / 1 to 1 / 11) oligomers, isobutylene oligomers (7 to 8 mers), and α-olefin (carbon number 5 to 20) oligomers (4 to 8 mers), etc., including mixed alkyl groups containing such residues.,

[0040] As the combination of at least two kinds of the above (meth)acrylic acid alkyl ester monomers, a combination of at least two compounds selected from the group consisting of 2-ethylhexyl (meth)acrylate, iso-butyl (meth)acrylate, isononyl (meth)acrylate and isodecyl (meth)acrylate is preferable. More preferably, it is a combination with at least one compound selected from the group consisting of 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, iso-butyl methacrylate, iso-butyl acrylate, isononyl acrylate and isodecyl acrylate. Even more preferably, (i) a combination of 2-ethylhexyl methacrylate and 2-ethylhexyl acrylate, (ii) a combination of 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate and iso-butyl methacrylate, (iii) a combination of iso-butyl methacrylate and iso-butyl acrylate, (iv) a combination of 2-ethylhexyl methacrylate and isononyl acrylate, or (iv) a combination of 2-ethylhexyl methacrylate and isodecyl acrylate.

[0041] The total content of the structural units derived from the above (meth)acrylic acid alkyl ester monomer in the (meth)acrylic polymer is preferably 91 to 97% by weight based on the weight of the (meth)acrylic polymer. When the total content of the structural units derived from the above (meth)acrylic acid alkyl ester monomer is within the above range, the strength of the electrode produced using the (meth)acrylic polymer is high, and the electrolyte permeability of the electrode becomes appropriate. Also, the adhesion to the metal foil of the (meth)acrylic polymer is excellent. More preferably, it is 92 to 96.5% by weight. The weight ratio (wt%) of the (meth)acrylic acid alkyl ester monomer can be measured by a method such as dissolving the polymer in a supercritical fluid and analyzing the obtained oligomer component by gas chromatography-mass spectrometry (GC-MS).

[0042] (Carboxylic acid-containing vinyl compound) Examples of the vinyl compound containing a carboxylic acid include those having 3 to 9 carbon atoms among known vinyl compounds containing a carboxylic acid, such as 2-ethylhexyl acrylate. Examples of such vinyl compounds containing a carboxylic acid include (meth)acrylic acid, butanoic acid (including substituted butanoic acids such as 2-methylbutanoic acid and 3-methylbutanoic acid), pentenoic acid (including substituted pentenoic acids such as 2-methylpentenoic acid and 3-methylpentenoic acid), hexenoic acid (including substituted hexenoic acids such as 2-methylhexenoic acid and 3-methylhexenoic acid), heptenoic acid (including substituted heptenoic acids such as 2-methylheptenoic acid and 3-methylheptenoic acid), and octenoic acid (including substituted octenoic acids such as 2-methyloctenoic acid and 3-methyloctenoic acid). As the vinyl compound containing a carboxylic acid, methacrylic acid or acrylic acid is preferred.

[0043] (Meth)acrylic polymers preferably have a total content of structural units derived from the vinyl compound containing a carboxylic acid of 3 to 9% by weight based on the weight of the (meth)acrylic polymer. When the total content of the structural units derived from the vinyl compound containing a carboxylic acid is within the above range, by-products such as lithium hydroxide generated in the battery can be neutralized, and corrosion of the electrodes can be prevented. More preferably, it is 3.5 to 7.0% by weight. The weight ratio (% by weight) of the vinyl compound containing a carboxylic acid can be measured by methods such as analyzing the oligomer component by gas chromatography-mass spectrometry (GC-MS) as described above.

[0044] As the structural units of the (meth)acrylic polymer, in addition to the (meth)acrylic acid alkyl ester monomer having a branched alkyl group and the vinyl compound containing a carboxylic acid, a (meth)acrylic acid alkyl ester monomer having no branched alkyl group may be used. Examples of the (meth)acrylic acid alkyl ester monomer having no branched alkyl group include, for example, a (meth)acrylic acid alkyl ester monomer having a linear alkyl group having 4 to 12 carbon atoms, a di(meth)acrylate of a diol having 2 to 12 carbon atoms, and the like.

[0045] Examples of the (meth)acrylic acid alkyl ester monomer having a linear alkyl group with 4 to 12 carbon atoms include butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, and the like. Examples of the di(meth)acrylate of a diol having 2 to 12 carbon atoms include ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, dodecanediol di(meth)acrylate, and the like. As the (meth)acrylic acid alkyl ester monomer having no branched alkyl group, butyl (meth)acrylate and 1,6-hexanediol di(meth)acrylate are preferable, and butyl acrylate and 1,6-hexanediol dimethacrylate are more preferable.

[0046] From the viewpoint of the strength of the electrode, when the (meth)acrylic acid alkyl ester monomer having no branched alkyl group is included as a constituent unit, its weight ratio is preferably 0.1 to 5% by weight based on the weight of the (meth)acrylic polymer.

[0047] The weight average molecular weight of the (meth)acrylic polymer is preferably 65,000 to 200,000. When the weight average molecular weight of the (meth)acrylic polymer is within the above range, the mechanical strength of the electrode is improved. More preferably, it is 75,000 to 185,000. In the method for obtaining the (meth)acrylic polymer described later, the weight average molecular weight can be adjusted to a desired range by adjusting the polymerization conditions.

[0048] The weight average molecular weight of the (meth)acrylic polymer in this specification is measured by gel permeation chromatography (hereinafter abbreviated as GPC) measured under the following conditions. <Measurement conditions of GPC> Apparatus: Alliance GPC V2000 (manufactured by Waters) Solvent: ortho-dichlorobenzene Standard substance: polystyrene Sample concentration: 3 mg / ml Column stationary phase: PLgel 10μm, MIXED-B 2 in series (manufactured by Polymer Laboratories) Column temperature: 135 °C

[0049] (Meth)acrylic polymers preferably have an SP value of 9.10 to 9.30. The SP value of the (meth)acrylic polymer in this specification is the solubility parameter [unit: (cal / cm 3 ) 1 / 2 and is calculated by the method described in the following literature proposed by Fedors et al. "POLYMER ENGINEERING AND SCIENCE, February, 1974, Vol. 14, No. 2, Robert F. Fedors (pages 147 - 154)".

[0050] The glass transition temperature of the (meth)acrylic polymer [hereinafter abbreviated as Tg, measurement method: DSC (differential scanning calorimetry) method] is preferably 20 °C or lower, more preferably -30 to 0 °C, and can be appropriately adjusted according to the type and weight of each monomer.

[0051] (Meth)acrylic polymers can be obtained by polymerizing a monomer composition containing at least two (meth)acrylic acid alkyl ester monomers having a branched alkyl group and a carboxylic acid-containing vinyl compound as essential components, and optionally (meth)acrylic acid alkyl ester monomers having no branched alkyl group as constituent components. As the polymerization method, known polymerization methods (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) can be used. Upon polymerization, known polymerization initiators {azo initiators [such as 2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(2-methylbutyronitrile), etc.], peroxide initiators (such as benzoyl peroxide, di-t-butyl peroxide, and lauryl peroxide, etc.), etc.} can be used. The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomer components contained in the monomer composition.

[0052] As the solvent used in solution polymerization, ester solvents [preferably ester compounds having 2 to 8 carbon atoms (such as ethyl acetate and butyl acetate)], alcohols [preferably aliphatic alcohols having 1 to 8 carbon atoms (such as methanol, ethanol, isopropanol, and octanol)], hydrocarbons having a straight-chain, branched, or cyclic structure with 5 to 8 carbon atoms (such as pentane, hexane, heptane, octane, cyclohexane, toluene, and xylene), amide solvents [such as N,N-dimethylformamide (hereinafter abbreviated as DMF) and dimethylacetamide], and ketone solvents [preferably ketone compounds having 3 to 9 carbon atoms (such as methyl ethyl ketone)] can be mentioned. The amount used is usually 50 to 200% by weight based on the total weight of the monomer components contained in the monomer composition, and the concentration of the monomer composition is usually 30 to 70% by weight.

[0053] As the solvent (dispersion medium) used in emulsion polymerization and suspension polymerization, water, alcohol (such as ethanol), ester solvent (such as ethyl propionate), and light naphtha can be mentioned. As emulsifiers, metal salts of higher fatty acids (having 10 to 24 carbon atoms) (such as sodium oleate and sodium stearate), metal salts of sulfuric esters of higher alcohols (having 10 to 24 carbon atoms) (such as sodium lauryl sulfate), ethoxylated tetramethyldecanediol, sodium sulfomethyl methacrylate, and dimethylaminomethyl methacrylate can be mentioned. Furthermore, polyvinyl alcohol, polyvinylpyrrolidone, etc. may be added as stabilizers. In emulsion polymerization or suspension polymerization, the concentration of the monomer composition is usually 5 to 95% by weight, and the amount of the polymerization initiator used is usually 0.01 to 5% by weight, preferably 0.05 to 2% by weight based on the total weight of the monomer composition, from the viewpoints of adhesive force and cohesive force. In the polymerization, known chain transfer agents such as mercapto compounds (e.g., dodecyl mercaptan and n-butyl mercaptan) and halogenated hydrocarbons (e.g., carbon tetrachloride, carbon tetrabromide, and benzyl chloride) can be used. The amount used is usually 2% by weight or less, preferably 0.5% by weight or less based on the total weight of the monomer components contained in the monomer composition, from the viewpoints of resin strength and the like.

[0054] Also, the temperature inside the system in the polymerization reaction is usually -5 to 150 °C, preferably 30 to 120 °C, the reaction time is usually 0.1 to 50 hours, preferably 2 to 24 hours, and the end point of the polymerization reaction is the point at which the amount of unreacted monomer is usually 5% by weight or less, preferably 1% by weight or less based on the total weight of the monomer components contained in the monomer composition, and the amount of unreacted monomer can be confirmed by a known method for quantifying the monomer content such as gas chromatography.

[0055] The polymer compound is not limited to the above-mentioned (meth)acrylic polymer. As the polymer compound, for example, a resin containing a polymer having an acrylic monomer (a) as an essential constituent monomer may be used. The polymer compound may contain both a polymer having an acrylic monomer (a) as an essential constituent monomer described below and the above-mentioned (meth)acrylic polymer.

[0056] Specifically, the polymer compound constituting the coating layer may be a polymer of a monomer composition containing acrylic acid (a0) as the acrylic monomer (a). In the above monomer composition, the content of acrylic acid (a0) is preferably more than 90% by weight and 98% by weight or less based on the weight of the whole monomer. From the viewpoint of the flexibility of the coating layer, the content of acrylic acid (a0) is more preferably 93.0 to 97.5% by weight, and even more preferably 95.0 to 97.0% by weight based on the weight of the whole monomer.

[0057] The polymer compound constituting the coating layer may contain, as the acrylic monomer (a), a monomer (a1) having a carboxyl group or acid anhydride group other than acrylic acid (a0).

[0058] Examples of the monomer (a1) having a carboxyl group or acid anhydride group other than acrylic acid (a0) include monocarboxylic acids having 3 to 15 carbon atoms such as methacrylic acid, crotonic acid, and cinnamic acid; dicarboxylic acids having 4 to 24 carbon atoms such as (anhydrous) maleic acid, fumaric acid, (anhydrous) itaconic acid, citraconic acid, and mesaconic acid; and polycarboxylic acids having 6 to 24 carbon atoms and a trivalent to tetravalent or higher valence such as aconitic acid.

[0059] The polymer compound constituting the coating layer may contain, as the acrylic monomer (a), a monomer (a2) represented by the following general formula (2). CH2=C(R 3 )COOR 4 (2) [In formula (2), R 3 is a hydrogen atom or a methyl group, and R 4 is a linear alkyl group having 4 to 12 carbon atoms or a branched alkyl group having 3 to 36 carbon atoms.]

[0060] In the monomer (a2) represented by the general formula (2), R 3 represents a hydrogen atom or a methyl group. R 3 is preferably a methyl group. R 4 is preferably a linear or branched alkyl group having 4 to 12 carbon atoms, or a branched alkyl group having 13 to 36 carbon atoms. Examples of the monomer (a2) include an ester compound (a21) in which R 4 is a linear or branched alkyl group having 4 to 12 carbon atoms, and an ester compound (a22) in which R 4 is a branched alkyl group having 13 to 36 carbon atoms.

[0061] R 4In the ester compound (a21) where the group is a linear or branched alkyl group having 4 to 12 carbon atoms, examples of the linear alkyl group having 4 to 12 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, and a dodecyl group. Examples of branched alkyl groups having 4 to 12 carbon atoms include 1-methylpropyl group (sec-butyl group), 2-methylpropyl group, 1,1-dimethylethyl group (tert-butyl group), 1-methylbutyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group (neopentyl group), 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, 1-methylhexyl group, 2-methylhexyl group, 2-methylhexyl group, 4-methylhexyl group, 5-methylhexyl group, 1-ethylpentyl group, 2-ethylpentyl group, 3-ethylpentyl group, 1,1-dimethylpentyl group, 1,2-dimethylpentyl group, 1,3-dimethylpentyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2-ethylpentyl group, 1-methylheptyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methylheptyl group, 5-methylheptyl group, 6-methylheptyl group, 1,1-dimethylhexyl group, 1,2-dimethylhexyl group, 1,3-dimethylhexyl group, 1,4-dimethylhexyl group, 1,5-dimethylhexyl group, 1-ethylhexyl group, 2-ethylhexyl group, 1-methyloctyl group, 2-methyloctyl group, 3-methyloctyl group, 4-methyloctyl group, 5-methyloctyl group, 6-methyloctyl group, 7-methyloctyl group, 1,1-dimethylheptyl group, 1,2-dimethylheptyl group, 1,3-dimethylheptyl group, 1,4-dimethylheptyl group, 1,5-dimethylheptyl group, 1,6-dimethylheptyl group, 1-ethylheptyl group, 2-ethylheptyl group, 1-methylnonyl group, 2-methylnonyl group, 3-methylnonyl group, 4-methylnonyl group, 5-methylnonyl group, 6-methylnonyl group, 7-methylnonyl group, 8-methylnonyl group, 1,1-dimethyloctyl group, 1,2-dimethyloctyl group, 1,3-dimethyloctyl group, 1,4-dimethyloctyl group, 1,5-dimethyloctyl group, 1,6-dimethyloctyl group, 1,7-dimethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 1-methyldecyl group, 2-methyldecyl group, 3-methyldecyl group, 4-methyldecyl group, 5-methyldecyl group, 6-methyldecyl group, 7-methyldecyl group, 8-methyldecyl group, 9-methyldecyl group, 1,1-dimethylnonyl group, 1,2-dimethylnonyl group, 1,3-dimethylnonyl group, 1,4-dimethylnonyl group, 1,5-dimethylnonyl group, 1,6-dimethylnonyl group, 1,7-dimethylnonyl group, 1,8-dimethylnonyl group, 1-ethylnonyl group, 2-ethylnonyl group, 1-methylundecyl group, 2-methylundecyl group, 3-methylundecyl group, 4-methylundecyl group, 5-methylundecyl group, 6-methylundecyl group, 7-methylundecyl group, 8-methylundecyl group, 9-methylundecyl group, 10-methylundecyl group, 1,1-dimethyldecyl group, 1,2-dimethyldecyl group, 1,3-dimethyldecyl group, 1,4-dimethyldecyl group, 1,5-dimethyldecyl group, 1,6-dimethyldecyl group, 1,7-dimethyldecyl group, 1,8-dimethyldecyl group, 1,9-dimethyldecyl group, 1-ethyldecyl group, 2-ethyldecyl group and the like can be mentioned. Among these, particularly, 2-ethylhexyl group is preferable.,

[0062] R 4In the ester compound (a22) where the branched alkyl group has 13 to 36 carbon atoms, examples of the branched alkyl group having 13 to 36 carbon atoms include 1-alkylalkyl groups [1-methyldodecyl group, 1-butyleicosyl group, 1-hexyloctadecyl group, 1-octylhexadecyl group, 1-decyltetradecyl group, 1-undecyltridecyl group, etc.], 2-alkylalkyl groups [2-methyldodecyl group, 2-hexyloctadecyl group, 2-octylhexadecyl group, 2-decyltetradecyl group, 2-undecyltridecyl group, 2-dodecylhexadecyl group, 2-tridecylpentadecyl group, 2-decyloctadecyl group, 2-tetradecyloctadecyl group, 2-hexadecyloctadecyl group, 2-tetradecyleicosyl group, 2-hexadecyloctadecyl group, etc.], 3 to 34-alkylalkyl groups (3-alkylalkyl group, 4-alkylalkyl group, 5-alkylalkyl group, 32-alkylalkyl group, 33-alkylalkyl group, 34-alkylalkyl group, etc.), and mixed alkyl groups containing one or more branched alkyl groups such as residues obtained by removing hydroxyl groups from oxo alcohols obtained from propylene oligomers (7 to 11 mers), ethylene / propylene (molar ratio 16 / 1 to 1 / 11) oligomers, isobutylene oligomers (7 to 8 mers), and α-olefin (carbon number 5 to 20) oligomers (4 to 8 mers).

[0063] The polymer compound constituting the coating layer may contain, as the acrylic monomer (a), an ester compound (a3) of a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth)acrylic acid. Examples of the monovalent aliphatic alcohol having 1 to 3 carbon atoms constituting the ester compound (a3) include methanol, ethanol, 1-propanol, 2-propanol, etc. Note that (meth)acrylic acid means acrylic acid or methacrylic acid.

[0064] The polymer compound constituting the coating layer is preferably a polymer of a monomer composition containing acrylic acid (a0) and at least one of monomer (a1), monomer (a2), and ester compound (a3), more preferably a polymer of a monomer composition containing acrylic acid (a0) and at least one of monomer (a1), ester compound (a21), and ester compound (a3), even more preferably a polymer of a monomer composition containing acrylic acid (a0) and any one of monomer (a1), monomer (a2), and ester compound (a3), and most preferably a polymer of a monomer composition containing acrylic acid (a0) and any one of monomer (a1), ester compound (a21), and ester compound (a3). Examples of the polymer compound constituting the coating layer include a copolymer of acrylic acid and maleic acid using maleic acid as monomer (a1), a copolymer of acrylic acid and 2-ethylhexyl methacrylate using 2-ethylhexyl methacrylate as monomer (a2), a copolymer of acrylic acid and methyl methacrylate using methyl methacrylate as ester compound (a3), and the like.

[0065] From the viewpoint of suppressing the volume change of the electrode active material particles and the like, the total content of monomer (a1), monomer (a2), and ester compound (a3) is preferably 2.0 to 9.9% by weight, more preferably 2.5 to 7.0% by weight, based on the weight of the entire monomer.

[0066] The polymer compound constituting the coating layer preferably does not contain a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group as acrylic monomer (a).

[0067] Examples of the structure having a polymerizable unsaturated double bond include a vinyl group, an allyl group, a styrenyl group, and a (meth)acryloyl group. Examples of the anionic group include a sulfonic acid group and a carboxyl group. An anionic monomer having a conjugated unsaturated double bond and an anionic group is a compound obtained by combining these, and examples thereof include vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, and (meth)acrylic acid. Note that the (meth)acryloyl group means an acryloyl group or a methacryloyl group. Examples of the cation constituting the salt (a4) of the anionic monomer include lithium ion, sodium ion, potassium ion, and ammonium ion.

[0068] In addition, the polymer compound constituting the coating layer may contain a radically polymerizable monomer (a5) copolymerizable with acrylic acid (a0), monomer (a1), monomer (a2), and ester compound (a3) as the acrylic monomer (a) within a range not impairing the physical properties. As the radically polymerizable monomer (a5), a monomer not containing active hydrogen is preferable, and the monomers of the following (a51) to (a58) can be used.

[0069] (a51) Hydrocarbyl (meth)acrylate formed from a linear aliphatic monool having 13 to 20 carbon atoms, an alicyclic monool having 5 to 20 carbon atoms, or an araliphatic monool having 7 to 20 carbon atoms and (meth)acrylic acid Examples of the above monool include (i) linear aliphatic monools (tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecyl alcohol, arachidyl alcohol, etc.), (ii) alicyclic monools (cyclopentyl alcohol, cyclohexyl alcohol, cycloheptyl alcohol, cyclooctyl alcohol, etc.), (iii) araliphatic monools (benzyl alcohol, etc.), and mixtures of two or more of these.

[0070] (a52) Poly(n = 2 - 30)oxyalkylene (carbon number 2 - 4) alkyl (carbon number 1 - 18) ether (meth)acrylate [ethylene oxide (hereinafter abbreviated as EO) 10 - mole adduct of methanol (meth)acrylate, propylene oxide (hereinafter abbreviated as PO) 10 - mole adduct of methanol (meth)acrylate, etc.]

[0071] (a53) Nitrogen - containing vinyl compound (a53 - 1) Amide - group - containing vinyl compound (i) (Meth)acrylamide compounds having 3 - 30 carbon atoms, for example, N,N - dialkyl (carbon number 1 - 6) or diarylalkyl (carbon number 7 - 15) (meth)acrylamide (N,N - dimethylacrylamide, N,N - dibenzylacrylamide, etc.), diacetoneacrylamide (ii) Amide - group - containing vinyl compounds having 4 - 20 carbon atoms excluding the above - mentioned (meth)acrylamide compounds, for example, N - methyl - N - vinylacetamide, cyclic amides [pyrrolidone compounds (carbon number 6 - 13, for example, N - vinylpyrrolidone, etc.)]

[0072] (a53 - 2) (Meth)acrylate compound (i) Dialkyl (carbon number 1 - 4) aminoalkyl (carbon number 1 - 4) (meth)acrylate [N,N - dimethylaminoethyl (meth)acrylate, N,N - diethylaminoethyl (meth)acrylate, t - butylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, etc.] (ii) Quaternary ammonium group - containing (meth)acrylate {quaternized products of tertiary amino group - containing (meth)acrylate [N,N - dimethylaminoethyl (meth)acrylate, N,N - diethylaminoethyl (meth)acrylate, etc.] (quaternized using quaternizing agents such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate, etc.)}

[0073] (a53 - 3) Heterocyclic - containing vinyl compound Pyridine compounds (having 7 to 14 carbon atoms, such as 2- or 4-vinylpyridine), imidazole compounds (having 5 to 12 carbon atoms, such as N-vinylimidazole), pyrrole compounds (having 6 to 13 carbon atoms, such as N-vinylpyrrole), pyrrolidone compounds (having 6 to 13 carbon atoms, such as N-vinyl-2-pyrrolidone)

[0074] (a53-4) Nitrile group-containing vinyl compounds Nitrile group-containing vinyl compounds having 3 to 15 carbon atoms, such as (meth)acrylonitrile, cyanostyrene, cyanoalkyl (having 1 to 4 carbon atoms) acrylate

[0075] (a53-5) Other nitrogen-containing vinyl compounds Nitro group-containing vinyl compounds (having 8 to 16 carbon atoms, such as nitrostyrene), etc.

[0076] (a54) Vinyl hydrocarbons (a54-1) Aliphatic vinyl hydrocarbons Olefins having 2 to 18 or more carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), dienes having 4 to 10 or more carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.), etc.

[0077] (a54-2) Alicyclic vinyl hydrocarbons Cyclic unsaturated compounds having 4 to 18 or more carbon atoms, such as cycloalkenes (e.g., cyclohexene), (di)cycloalkadienes [e.g., (di)cyclopentadiene], terpenes (e.g., pinene and limonene), indene

[0078] (a54-3) Aromatic vinyl hydrocarbons Aromatic unsaturated compounds having 8 to 20 or more carbon atoms, such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene

[0079] (a55) Vinyl ester Aliphatic vinyl ester [carbon number 4 - 15, for example alkenyl esters of aliphatic carboxylic acids (mono - or dicarboxylic acids) (e.g., vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, vinyl methoxyacetate)] Aromatic vinyl ester [carbon number 9 - 20, for example alkenyl esters of aromatic carboxylic acids (mono - or dicarboxylic acids) (e.g., vinyl benzoate, diallyl phthalate, methyl - 4 - vinylbenzoate), esters of aliphatic carboxylic acids containing an aromatic ring (e.g., acetoxystyrene)]

[0080] (a56) Vinyl ether Aliphatic vinyl ether [carbon number 3 - 15, for example vinyl alkyl (carbon number 1 - 10) ethers (vinyl methyl ether, vinyl butyl ether, vinyl 2 - ethylhexyl ether, etc.), vinyl alkoxy (carbon number 1 - 6) alkyl (carbon number 1 - 4) ethers (vinyl - 2 - methoxyethyl ether, methoxybutadiene, 3,4 - dihydro - 1,2 - pyran, 2 - butoxy - 2’ - vinyloxy diethyl ether, vinyl - 2 - ethylmercaptoethyl ether, etc.), poly(2 - 4)(meth)allyloxyalkane (carbon number 2 - 6) (diallyloxyethane, triallyloxyethane, tetraallyloxybutane, tetramethallyloxyethane, etc.)], aromatic vinyl ether (carbon number 8 - 20, for example vinyl phenyl ether, phenoxystyrene)

[0081] (a57) Vinyl ketone Aliphatic vinyl ketone (carbon number 4 - 25, for example vinyl methyl ketone, vinyl ethyl ketone), aromatic vinyl ketone (carbon number 9 - 21, for example vinyl phenyl ketone)

[0082] (a58) Unsaturated dicarboxylic acid diester Unsaturated dicarboxylic acid diesters having 4 to 34 carbon atoms, such as dialkyl fumarates (the two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms), dialkyl maleates (the two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms)

[0083] When containing the radically polymerizable monomer (a5), its content is preferably 0.1 to 3.0% by weight based on the total weight of the monomers.

[0084] The preferable lower limit of the weight average molecular weight of the polymer having the acrylic monomer (a) as an essential constituent monomer is 3,000, the more preferable lower limit is 5,000, and the further preferable lower limit is 7,000. On the other hand, the preferable upper limit of the weight average molecular weight of the above polymer compound is 100,000, and the more preferable upper limit is 70,000.

[0085] The weight average molecular weight of the polymer having the acrylic monomer (a) as an essential constituent monomer is measured under the measurement conditions of GPC described above.

[0086] The polymer having the acrylic monomer (a) as an essential constituent monomer can be produced by a known polymerization method (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) using a known polymerization initiator {azo initiators [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), etc.], peroxide initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.), etc.}. The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, and further preferably 0.1 to 1.5% by weight based on the total weight of the monomers from the viewpoints of adjusting the weight average molecular weight to a preferable range, etc. The polymerization temperature and the polymerization time are adjusted according to the type of the polymerization initiator, etc., but the polymerization temperature is preferably -5 to 150 °C, (more preferably 30 to 120 °C), and the reaction time is preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

[0087] Examples of solvents used in solution polymerization include esters (having 2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (having 1 to 8 carbon atoms, such as methanol, ethanol, and octanol), hydrocarbons (having 4 to 8 carbon atoms, such as n-butane, cyclohexane, and toluene), amides (such as N,N-dimethylformamide (hereinafter abbreviated as DMF)), and ketones (having 3 to 9 carbon atoms, such as methyl ethyl ketone). From the viewpoint of adjusting the weight average molecular weight to a preferable range, etc., the usage amount is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, still more preferably 30 to 300% by weight based on the total weight of the monomers. The monomer concentration is preferably 10 to 95% by weight, more preferably 20 to 90% by weight, still more preferably 30 to 80% by weight.

[0088] Examples of dispersion media in emulsion polymerization and suspension polymerization include water, alcohols (such as ethanol), esters (such as ethyl propionate), light naphtha, etc. Examples of emulsifiers include metal salts of higher fatty acids (having 10 to 24 carbon atoms, such as sodium oleate and sodium stearate), metal salts of sulfuric acid esters of higher alcohols (having 10 to 24 carbon atoms, such as sodium lauryl sulfate), ethoxylated tetramethyldecanediol, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. Further, polyvinyl alcohol, polyvinylpyrrolidone, etc. may be added as stabilizers. The monomer concentration of the solution or dispersion is preferably 5 to 95% by weight, more preferably 10 to 90% by weight, still more preferably 15 to 85% by weight. The usage amount of the polymerization initiator is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight based on the total weight of the monomers. In the polymerization, known chain transfer agents such as mercapto compounds (dodecyl mercaptan, n-butyl mercaptan, etc.) and / or halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.) can be used.

[0089] The polymer compound constituting the coating layer may be a crosslinked polymer obtained by crosslinking the polymer compound with a crosslinking agent (A') having a reactive functional group that reacts with a carboxyl group {preferably a polyepoxy compound (a'1) [polyglycidyl ether (bisphenol A diglycidyl ether, propylene glycol diglycidyl ether, glycerin triglycidyl ether, etc.) and polyglycidylamine (N,N-diglycidylaniline and 1,3-bis(N,N-diglycidylaminomethyl)) and the like] and / or a polyol compound (a'2) (ethylene glycol, etc.)}.

[0090] As a method of crosslinking the polymer compound constituting the coating layer using the crosslinking agent (A'), there is a method of crosslinking the electrode active material particles after coating them with the polymer compound constituting the coating layer.Specifically, there is a method of producing coated electrode active material particles by mixing the electrode active material particles with a resin solution containing the polymer compound constituting the coating layer and removing the solvent, and then mixing the coated electrode active material particles with a solution containing the crosslinking agent (A') and heating the mixture to cause desolvation and crosslinking reaction, and a reaction in which the polymer compound constituting the coating layer is crosslinked by the crosslinking agent (A') occurs on the surface of the electrode active material particles. The heating temperature is adjusted depending on the type of crosslinking agent, but is preferably 70°C or higher when a polyepoxy compound (a'1) is used as the crosslinking agent, and is preferably 120°C or higher when a polyol compound (a'2) is used.

[0091] (Conductive assistant) Examples of the conductive assistant include metals [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon [graphite (flaky graphite (UP)), carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.) and carbon nanofibers (CNF), etc.], and mixtures thereof.

[0092] When the coating layer contains a conductive aid, the ratio of the polymer compound constituting the coating layer to the conductive aid is not particularly limited. However, from the viewpoint of the internal resistance of the battery, etc., the weight ratio of the polymer compound (resin solid content weight) constituting the coating layer: conductive aid is preferably 1:0.01 to 1:50, and more preferably 1:0.2 to 1:3.0.

[0093] In the coated electrode active material particles for a lithium ion battery of the present invention, the coating layer may further contain ceramic particles.

[0094] Examples of the ceramic particles include metal carbide particles, metal oxide particles, glass ceramic particles, etc.

[0095] Examples of the metal carbide particles include silicon carbide (SiC), tungsten carbide (WC), molybdenum carbide (Mo2C), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), vanadium carbide (VC), zirconium carbide (ZrC), etc.

[0096] Examples of the metal oxide particles include zinc oxide (ZnO), aluminum oxide (Al2O3), silicon dioxide (SiO2), tin oxide (SnO2), titania (TiO2), zirconia (ZrO2), indium oxide (In2O3), Li2B4O7, Li4Ti5O 12 、Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, and perovskite type oxide particles represented by ABO3 (wherein A is at least one selected from the group consisting of Ca, Sr, Ba, La, Pr, and Y, and B is at least one selected from the group consisting of Ni, Ti, V, Cr, Mn, Fe, Co, Mo, Ru, Rh, Pd, and Re), etc. As metal oxide particles, zinc oxide (ZnO), aluminum oxide (Al2O3), silicon dioxide (SiO2), and lithium tetraborate (Li2B4O7) are preferable from the viewpoint of suitably suppressing side reactions occurring between the electrolytic solution and the coated electrode active material particles.

[0097] The glass-ceramic particles are preferably a lithium-containing phosphate compound having a rhombohedral crystal system, and its chemical formula is Li x M”2P3O 12 (X = 1 to 1.7). Here, M” is one or more elements selected from the group consisting of Zr, Ti, Fe, Mn, Co, Cr, Ca, Mg, Sr, Y, Sc, Sn, La, Ge, Nb, and Al. Also, a part of P may be substituted with Si or B, and a part of O may be substituted with F, Cl, etc. For example, Li 1.15 Ti 1.85 Al 0.15 Si 0.05 P 2.95 O 12 , Li 1.2 Ti 1.8 Al 0.1 Ge 0.1 Si 0.05 P 2.95 O 12 etc. can be used. Also, materials with different compositions may be mixed or compounded, or the surface may be coated with a glass electrolyte or the like. Or, it is preferable to use glass-ceramic particles in which a crystal phase of a lithium-containing phosphate compound having a NASICON-type structure is precipitated by heat treatment. Examples of the glass electrolyte include the glass electrolyte described in JP-A-2019-96478.

[0098] Here, the blending ratio of Li2O in the glass-ceramic particles is preferably 8% by mass or less in terms of oxide. Even if it does not have a NASICON structure, it consists of one or more elements selected from the group consisting of Li, La, Mg, Ca, Fe, Co, Cr, Mn, Ti, Zr, Sn, Y, Sc, P, Si, O, In, Nb, and F, has a crystal structure of LISICON type, perovskite type, β-Fe2(SO4)3 type, or Li3In2(PO4)3 type, and conducts Li ions at room temperature at 1×10 -5 A solid electrolyte that conducts S / cm or more may be used.

[0099] The above-described ceramic particles may be used alone or in combination of two or more.

[0100] From the viewpoints of energy density and electrical resistance value, the volume average particle diameter of the ceramic particles is preferably 1 to 1000 nm, more preferably 1 to 500 nm, and even more preferably 1 to 150 nm.

[0101] When the coating layer contains ceramic particles, the weight ratio of the ceramic particles is preferably 0.5 to 5.0% by weight based on the weight of the coated electrode active material particles. By containing the ceramic particles within the above range, side reactions occurring between the electrolytic solution and the coated electrode active material particles can be preferably suppressed. The weight ratio of the ceramic particles is more preferably 2.0 to 4.0% by weight based on the weight of the coated electrode active material particles.

[0102] The coated electrode active material particles may have two or more coating layers. When there are two or more coating layers, the composition of the polymer compound contained in each coating layer may be the same or different. Also, the types of conductive aids contained in each coating layer may be the same or different. Further, when the coating layer contains ceramic particles, the types of conductive aids contained in each coating layer may be the same or different.

[0103] The method for manufacturing the coated electrode active material particles preferably includes a step of removing the solvent after mixing electrode active material particles, a polymer compound, a conductive assistant, optionally used ceramic particles, and an organic solvent.

[0104] The organic solvent is not particularly limited as long as it can dissolve the polymer compound, and known organic solvents can be appropriately selected and used.

[0105] In the method for manufacturing the coated electrode active material particles, first, electrode active material particles, a polymer compound constituting the coating layer, a conductive assistant, and optionally used ceramic particles are mixed in an organic solvent. The order of mixing the electrode active material particles, the polymer compound constituting the coating layer, the conductive assistant, and the ceramic particles is not particularly limited. For example, a resin composition composed of a previously mixed polymer compound, conductive assistant, and ceramic particles constituting the coating layer may be further mixed with the electrode active material particles, or the electrode active material particles, the polymer compound constituting the coating layer, the conductive assistant, and the ceramic particles may be mixed simultaneously, or the polymer compound constituting the coating layer may be mixed with the electrode active material particles, and then the conductive assistant and the ceramic particles may be further mixed.

[0106] The coated electrode active material particles can be obtained by coating the electrode active material particles with a coating layer containing a polymer compound, a conductive assistant, and optionally used ceramic particles. For example, the electrode active material particles are placed in a universal mixer and stirred at 30 to 500 rpm, and a resin solution containing the polymer compound and the conductive assistant constituting the coating layer is added dropwise and mixed over 1 to 90 minutes. When using ceramic particles, they are mixed, the temperature is raised to 50 to 200 °C while stirring, the pressure is reduced to 0.007 to 0.04 MPa, and then held for 10 to 150 minutes to remove the solvent, thereby obtaining the coated electrode active material particles.

[0107] The Carr's fluidity index and the like of the coated electrode active material particles may be adjusted by classifying the coated electrode active material particles obtained by the above steps using a sieve with a predetermined mesh size.

[0108] When the coating layer of the coated electrode active material particles has two layers, for example, after forming the first coating layer according to the above method, a resin solution containing a polymer compound constituting the second coating layer, a conductive assistant, and ceramic particles are used, and the second coating layer can be obtained on the first coating layer in the same procedure as the above method. When the coating layer of the coated electrode active material particles has three or more layers, the coated electrode active material particles can be obtained in the same manner by forming a coating layer on the surface of the electrode active material particles.

[0109] The blending ratio of the electrode active material particles and the resin composition containing the polymer compound constituting the coating layer, the conductive assistant, and optionally used ceramic particles is not particularly limited, but it is preferably 1:0.001 to 0.1 in terms of weight ratio of the electrode active material particles:resin composition.

[0110] At least a part of the surface of the electrode active material particles is coated with a coating layer. From the viewpoint of cycle characteristics, the coating rate obtained by the following calculation formula is preferably 30 to 95% for the electrode active material particles. Coating rate (%) = {1 - [BET specific surface area of the coated electrode active material particles / (BET specific surface area of the electrode active material particles before coating × weight ratio of the electrode active material particles contained in the coated electrode active material particles + BET specific surface area of the conductive assistant × weight ratio of the conductive assistant contained in the coated electrode active material particles + BET specific surface area of the ceramic particles × weight ratio of the ceramic particles contained in the coated electrode active material particles)]} × 100

[0111] [Electrode for lithium-ion battery] The electrode for a lithium-ion battery of the present invention includes the coated electrode active material particles for a lithium-ion battery of the present invention.

[0112] The electrode for a lithium-ion battery of the present invention preferably comprises a non-binder containing the coated electrode active material particles for a lithium-ion battery of the present invention and a conductive assistant. Here, the non-bonded body means that the coated electrode active material particles and the conductive assistant are not fixed in position by a binder (also referred to as a binder). That is, the coated electrode active material particles and the conductive assistant are in a state where they can move according to an external force respectively.

[0113] When the electrode is composed of a non-bonded body, the coated electrode active material particles and the conductive assistant are not irreversibly fixed by a binder. Irreversible fixation means that the coated electrode active material particles and the conductive assistant are adhesively fixed by the following known solvent-drying type binder, and in order to separate the adhesively fixed coated electrode active material particles and the conductive assistant, it is necessary to mechanically break the interface between the coated electrode active material particles and the conductive assistant. On the other hand, in the case of a non-bonded body, since the coated electrode active material particles and the conductive assistant are not irreversibly adhesively fixed, they can be separated without mechanically breaking the interface between the coated electrode active material particles and the conductive assistant.

[0114] In the electrode of the present invention, it is preferably free of a solvent-drying type binder. Examples of the solvent-drying type binder include known non-aqueous secondary battery binders such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. These binders are used by dissolving or dispersing them in a solvent, and by volatilizing and distilling off the solvent, the surface solidifies without showing adhesiveness, and firmly fixes the coated electrode active material particles to each other, and the coated electrode active material particles, the conductive assistant, and the current collector.

[0115] The electrode of the present invention preferably includes an electrode active material layer containing coated electrode active material particles, a conductive assistant, and an electrolytic solution containing an electrolyte and a solvent.

[0116] As the electrolyte, an electrolyte used in a known electrolytic solution can be used. For example, lithium salts of inorganic anions such as LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, and LiN(FSO2)2, and lithium salts of organic anions such as LiN(CF3SO2)2, LiN(C2F5SO2)2, and LiC(CF3SO2)3 can be mentioned. Among these, LiN(FSO2)2 is preferable from the viewpoints of battery output and charge-discharge cycle characteristics.

[0117] As the solvent, a non-aqueous solvent used in a known electrolytic solution can be used. For example, a lactone compound, a cyclic or chain carbonate, a chain carboxylic acid ester, a cyclic or chain ether, a phosphate ester, a nitrile compound, an amide compound, a sulfone, sulfolane, and a mixture thereof can be used.

[0118] Examples of the lactone compound include lactone compounds of a 5-membered ring (such as γ-butyrolactone and γ-valerolactone) and a 6-membered ring (such as δ-valerolactone).

[0119] Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate (EC), and butylene carbonate (BC). Examples of the chain carbonate include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate.

[0120] Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

[0121] Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 1,4-dioxane. Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

[0122] Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, tripropyl phosphate, tributyl phosphate, tris(trifluoromethyl) phosphate, tris(trichloromethyl) phosphate, tris(trifluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphospholane-2-one, 2-trifluoroethoxy-1,3,2-dioxaphospholane-2-one, 2-methoxyethoxy-1,3,2-dioxaphospholane-2-one, and the like.

[0123] Examples of the nitrile compound include acetonitrile and the like. Examples of the amide compound include DMF and the like. Examples of the sulfone include dimethyl sulfone, diethyl sulfone, and the like.

[0124] These solvents may be used alone or in combination of two or more.

[0125] The concentration of the electrolyte in the electrolytic solution is preferably 1.2 to 5.0 mol / L, more preferably 1.5 to 4.5 mol / L, still more preferably 1.8 to 4.0 mol / L, and particularly preferably 2.0 to 3.5 mol / L. Such an electrolytic solution has appropriate viscosity, so that a liquid film can be formed between the coated electrode active material particles, and a lubricating effect (the ability to adjust the position of the coated electrode active material particles) can be imparted to the coated electrode active material particles.

[0126] The electrode of the present invention may contain a conductive auxiliary agent separately from the conductive auxiliary agent contained in the coating layer of the coated electrode active material particles described above. It can be distinguished in that the conductive auxiliary agent contained in the coating layer is integrated with the coated electrode active material particles, while the conductive auxiliary agent contained in the electrode is contained separately from the coated electrode active material particles. The conductive auxiliary agent contained in the electrode may be the same as or different from the conductive auxiliary agent contained in the coating layer. As the conductive auxiliary agent that the electrode of the present invention may contain, the same ones as those exemplified as the conductive auxiliary agent contained in the coating layer can be used.

[0127] The total content of the conductive assistant contained in the electrode and the conductive assistant contained in the coating layer is not particularly limited, but is preferably 0.5 to 20% by weight based on the weight obtained by removing the electrolytic solution from the electrode active material layer.

[0128] When the electrode of the present invention is a positive electrode, the thickness of the positive electrode active material layer is preferably 150 to 470 μm, more preferably 200 to 460 μm, from the viewpoint of battery performance.

[0129] When the electrode of the present invention is a negative electrode, the thickness of the negative electrode active material layer is preferably 150 to 650 μm, more preferably 200 to 620 μm, from the viewpoint of battery performance.

[0130] The electrode of the present invention can be produced, for example, by applying an electrode slurry containing coated electrode active material particles, a conductive assistant, and an electrolytic solution to a current collector and then drying it. Specifically, examples of the method include applying the electrode slurry onto the current collector using a coating device such as a bar coater, and then removing the solvent by allowing a non-woven fabric to stand on the active material to absorb the liquid, and, if necessary, pressing with a press machine.

[0131] In the electrode of the present invention, examples of the material constituting the current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as fired carbon, conductive polymer materials, conductive glass, and the like. The shape of the current collector is not particularly limited, and it may be a sheet-shaped current collector made of the above materials, or a deposited layer composed of fine particles made of the above materials. The thickness of the current collector is not particularly limited, but is preferably 50 to 500 μm.

[0132] Thus, the electrode of the present invention preferably further includes a current collector, and the electrode active material layer is provided on the surface of the current collector. For example, the electrode of the present invention may include a resin current collector made of a conductive polymer material.

[0133] As the conductive polymer material constituting the resin current collector, for example, a material obtained by adding a conductive agent to a resin can be used. As the conductive agent constituting the conductive polymer material, the same materials as those of the conductive aid for the coating layer can be preferably used. Examples of the resin constituting the conductive polymer material include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin, or a mixture thereof. From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and polycycloolefin (PCO) are preferred, and more preferably polyethylene (PE), polypropylene (PP), and polymethylpentene (PMP). The resin current collector can be obtained by a known method described in JP-A-2012-150905 and Re-2015 / 005116.

[0134] [Lithium Ion Single Battery] The lithium ion single battery of the present invention includes the electrode for a lithium ion battery of the present invention. By combining the positive electrode, which is the electrode for a lithium ion battery, and the negative electrode, which is the electrode for a lithium ion battery, and housing them together with a separator in a cell container, injecting an electrolytic solution, and sealing the cell container, a lithium ion single battery can be obtained. At this time, at least one of the positive electrode, which is the electrode for lithium ions, and the negative electrode, which is the electrode for lithium ions, is the electrode for a lithium ion battery of the present invention.

[0135] Examples of the separator include known separators for lithium-ion batteries such as a porous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and porous polypropylene, a non-woven fabric made of synthetic fibers (such as polyester fibers and aramid fibers) or glass fibers, and those with ceramic fine particles such as silica, alumina, and titania adhered to their surfaces.

[0136] The lithium-ion single battery preferably includes a laminated unit in which a positive electrode current collector, a positive electrode active material layer, a separator, a negative electrode active material layer, and a negative electrode current collector are laminated in this order. The lithium-ion single battery may be sealed with a sealing material around it so that the positive electrode current collector and the negative electrode current collector are exposed.

[0137] [Battery Module] The battery module of the present invention is formed by laminating a plurality of the lithium-ion single batteries of the present invention.

[0138] In the battery module, it is preferable that the negative electrode current collectors and the positive electrode current collectors of adjacent lithium-ion single batteries are laminated in series so as to be adjacent to each other. The laminated single batteries may be housed in a container.

[0139] It is preferable that the lithium-ion single batteries constituting the battery module are made of the same constituent materials.

[0140] The following matters are disclosed in this specification.

[0141] The present disclosure (1) is a coated electrode active material particle for a lithium-ion battery in which at least a part of the surface of the electrode active material particles is coated with a coating layer containing a polymer compound and a conductive assistant, and is characterized in that the Carr fluidity index is 55 to 65.

[0142] The present disclosure (2) is the coated electrode active material particle for a lithium-ion battery according to the present disclosure (1), in which the internal friction angle is 38.9° or more.

[0143] The present disclosure (3) is the coated electrode active material particles for a lithium-ion battery according to the present disclosure (1) or (2), wherein the shear adhesion force of the powder layer composed of the coated electrode active material particles for a lithium-ion battery at a vertical pressure of 20 kPa in a shear test based on JIS-Z8835 is 620 Pa or more.

[0144] The present disclosure (4) is the coated electrode active material particles for a lithium-ion battery according to any one of the present disclosures (1) to (3), wherein the average envelope area is 30 μm 2 or less, and / or the average envelope perimeter is 20 μm or less.

[0145] The present disclosure (5) is an electrode for a lithium-ion battery including the coated electrode active material particles for a lithium-ion battery according to any one of the present disclosures (1) to (4).

[0146] The present disclosure (6) is a lithium-ion single battery including the electrode for a lithium-ion battery according to the present disclosure (5).

[0147] The present disclosure (7) is a battery module in which a plurality of the lithium-ion single batteries according to the present disclosure (6) are stacked.

Examples

[0148] Next, the present invention will be specifically described by way of examples. However, the present invention is not limited to the examples as long as the gist of the present invention is not deviated from. Unless otherwise specified, "parts" means parts by weight.

[0149] [Preparation of Polymer Compound for Coating Electrode Active Material] A four-necked Kolbe equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 70 parts of 2-ethylhexyl methacrylate, 25 parts of 2-ethylhexyl acrylate, 5 parts of methacrylic acid and 150 parts of toluene, and the temperature was raised to 75 °C. 10 parts of toluene, 0.200 part of 2,2'-azobis(2,4-dimethylvaleronitrile) and 0.200 part of 2,2'-azobis(2-methylbutyronitrile) were mixed. While blowing nitrogen into the Kolbe, the obtained monomer mixture was continuously dropped through the dropping funnel over 4 hours with a polymerization initiator mixture to conduct radical polymerization. After the dropping was completed, a solution prepared by dissolving 0.800 part of 2,2'-azobis(2,4-dimethylvaleronitrile) in 12.4 parts of toluene was continuously added dropwise through the dropping funnel from 6 to 8 hours after the start of polymerization. Further, the polymerization was continued for 2 hours, and 150 parts of toluene was added to obtain a solution of (meth)acrylic polymer (C1) with a resin concentration of 25% by weight. When the molecular weight of the obtained (meth)acrylic polymer (C1) was measured by GPC, Mw was 110,000. The Tg of the obtained (meth)acrylic polymer (C1) was -15.4 °C and the SP value was 9.23.

[0150] [Preparation of Coated Cathode Active Material Particles] (Example 1) 85.0 parts of NCA (LiNi 0.8 Co 0.15 Al 0.05 O2 powder, volume average particle diameter 4 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, 22.4 parts (5.6 parts in terms of solid content) of a solution of (meth)acrylic polymer (C1), which is a polymer compound, was dropped over 2 minutes, and stirring was continued for another 5 minutes. Next, while stirring, 9.4 parts in total of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], which is a conductive aid, carbon nanofiber (CNF) [manufactured by Showa Denko K.K., trade name "VGCF"], and SiO2 (trade name "AEROSIL200 PE", manufactured by Nippon Aerosil Co., Ltd., volume average particle diameter 12 nm), which is a ceramic particle, were added in 2 minutes while being divided, and stirring was continued for 30 minutes. The weight ratio of graphite (UP):carbon nanofiber (CNF):SiO2 was made 3:1:2. Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140 °C while maintaining stirring and the degree of pressure reduction, and stirring, the degree of pressure reduction, and the temperature were maintained for 8 hours to distill off volatile components. The obtained powder was classified with a sieve having an aperture of 50 μm to obtain coated positive electrode active material particles P-1.

[0151] (Examples 2 to 6, Comparative Examples 1 to 3) The parts by weight of the positive electrode active material particles, polymer compound, conductive aid, and ceramic particles were the same as those described in Table 1, and the coated positive electrode active material particles P-2 to P-6 of the examples and the coated positive electrode active material particles P'-1 to P'-3 of the comparative examples were obtained in the same manner as in Example 1 except that the aperture of the sieve was the same as that described in Table 1. As the conductive aid and ceramic particles, graphite (UP):carbon nanofiber (CNF):SiO2 was added at a weight ratio of 3:1:2 in the same manner as in Example 1. In Table 1, the parts by weight of the (meth)acrylic polymer (C1), which is a polymer compound, indicate the parts by weight in terms of solid content.

[0152] The Carr's flowability index, internal friction angle, shear adhesion force, average envelope area, and average envelope perimeter of the coated positive electrode active material particles P-1 to P-6 of the examples and the coated positive electrode active material particles P'-1 to P'-3 of the comparative examples were measured by the following methods. The results are shown in Table 1.

[0153] <Measurement of Carr's flowability index> Using a multi-functional powder physical property measuring instrument (Seishin Enterprise Co., Ltd., Multi Tester MT-02), the angle of repose (°), compressibility (%), spatula angle (°), and uniformity (-) of the coated cathode active material particles were measured. The temperature during the measurement was 25°C, and the humidity was 50%. Referring to Table 2 of "Powder Technology Pocket Book" written by Tsunehiro Hayashi (published by Kogyo Chosa Kai, 1996), the indices corresponding to each measured value were obtained. By summing up the indices of each measured value, the Carr flowability index was obtained.

[0154] <Measurement of the angle of internal friction> The angle of internal friction of the coated cathode active material particles was measured using a powder flow tester (manufactured by Brookfield). The measurement conditions were as follows: a blade-type lid was used as the pusher, the vertical movement speed was 1.0 mm / second, and the rotation speed was 1 rotation / hour.

[0155] <Measurement of shear adhesion> Based on JIS-Z8835 (Method for Measuring the Critical State Line (CSL) and Wall Failure Line (WYL) by One-Side Shear Test), the shear adhesion of the powder layer composed of coated cathode active material particles at a vertical pressure of 20 kPa was measured using a shear-type powder flowability measuring machine (Volution Powder Tester, manufactured by Mercury Scientific) by the rotating cell constant volume method.

[0156] <Measurement of the average envelope area and average envelope perimeter> 3000 coated cathode active material particles were observed using a particle size and shape distribution measuring instrument (PITA-1 manufactured by Seishin Enterprise Co., Ltd.). Using the software (Image Analysis) attached to the device, the envelope perimeter and envelope area were measured, and the average envelope perimeter and average envelope area were obtained. At this time, propylene carbonate was used as the dispersion medium. A sample solution prepared by dispersing 0.1 g of coated cathode active material particles in propylene carbonate was used.

[0157]

Table 1

[0158] [Preparation of Coated Negative Electrode Active Material Particles] (Example 7) (Formation of the First Coating Layer) 74.5 parts of HC (hard carbon powder, volume average particle diameter 25 μm, manufactured by JFE Chemical Corporation), which is a negative electrode active material particle, was placed in a high-speed mixer FS25 [manufactured by Earth Technica Co., Ltd.], a universal mixer, and while stirring at room temperature and 720 rpm, 57.6 parts (14.4 parts in terms of solid content) of a solution of a (meth)acrylic polymer (C1), which is a polymer compound, was added dropwise over 2 minutes, and stirring was continued for another 5 minutes. Next, while stirring, graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], which is a conductive assistant, was added in parts by weight described later over 2 minutes while being divided, and stirring was continued for 30 minutes.

[0159] (Formation of the Second Coating Layer) Furthermore, while stirring, acetylene black (AB) [manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm], which is a conductive assistant, was added in parts by weight described later over 2 minutes while being divided, and stirring was continued for 30 minutes. Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, then the temperature was raised to 140 °C while maintaining stirring and the degree of pressure reduction, and stirring, the degree of pressure reduction, and the temperature were maintained for 8 hours to distill off volatile components. The obtained powder was classified with a sieve having an opening of 100 μm to obtain coated negative electrode active material particles N-1. The total amount of graphite (UP) added in the formation of the first coating layer and acetylene black (AB) added in the formation of the second coating layer was made to be 11.1 parts by weight. The weight ratio of graphite (UP):acetylene black (AB) was made to be 7:2.

[0160] (Examples 8 to 15, Comparative Examples 4 to 8) Coated negative electrode active material particles N-2 to N-9 of the examples and coated negative electrode active material particles N'-1 to N'-5 of the comparative examples were obtained in the same manner as in Example 7, except that the parts by weight of the negative electrode active material particles, the polymer compound, and the conductive assistant were as described in Table 2, and the opening of the sieve was as described in Table 2. In Table 2, the parts by weight of the (meth)acrylic polymer (C1), which is a polymer compound, are shown as parts by weight in terms of solid content. As the conductive auxiliary agent, graphite (UP): acetylene black (AB) was added in a weight ratio of 7:2, similar to Example 7. Among the negative electrode active material particles in Table 2, HC(25) means hard carbon powder with a volume average particle diameter of 25 μm. HC(20) means hard carbon powder with a volume average particle diameter of 20 μm. HC(5) means hard carbon powder with a volume average particle diameter of 5 μm.

[0161] The Carr's fluidity index, internal friction angle, shear adhesion force, average envelope area, and average envelope perimeter of the coated negative electrode active material particles N-1 to N-9 of the examples and the coated negative electrode active material particles N'-1 to N'-5 of the comparative examples were measured in the same manner as the positive electrode active material particles. The results are shown in Table 2.

[0162]

Table 2

[0163] [Fabrication of positive electrode] (Fabrication of conductive resin collector for positive electrode) Using a twin-screw extruder, 28 parts of random polypropylene [polypropylene resin, trade name "Sun Allomer PC630S", manufactured by Sun Allomer Co., Ltd.], 67 parts of acetylene black [conductive filler, Denka Black powder, manufactured by Denka Co., Ltd.], and 5 parts of dispersant [trade name "Yumex 1001", manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200 °C and 200 rpm to obtain a conductive resin composition for positive electrode. The obtained conductive resin composition for positive electrode was passed through a T-die extrusion film forming machine and stretched and rolled to obtain a conductive film for resin collector for positive electrode with a film thickness of 100 μm. Next, after cutting the obtained conductive film for resin collector for positive electrode to a size of 17.0 cm × 17.0 cm, a resin collector for positive electrode with a terminal for current extraction (5 mm × 3 cm) connected was fabricated.

[0164] (Fabrication of electrolyte) An electrolyte solution was prepared by dissolving LiN(FSO2)2 at a ratio of 2.0 mol / L in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1:1).

[0165] (Example 16) 42 parts of the electrolyte solution and 4.2 parts of carbon fiber [Donacarb Mild S-243 manufactured by Osaka Gas Chemical Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS / cm] were mixed at 2000 rpm for 5 minutes using a planetary stirring type mixing and kneading device {Avatori Rentaro [manufactured by Shinki Co., Ltd.]}, and then 30 parts of the above electrolyte solution and 206 parts of the above coated positive electrode active material particles P-1 were added. Thereafter, further mixing was carried out at 2000 rpm for 2 minutes using Avatori Rentaro, and after adding 20 parts of the above electrolyte solution, stirring by Avatori Rentaro was carried out at 2000 rpm for 1 minute. After further adding 2.3 parts of the above electrolyte solution, stirring by Avatori Rentaro was carried out at 2000 rpm for 2 minutes to prepare a positive electrode slurry. The obtained positive electrode slurry was applied to one side of a positive electrode resin current collector so that the basis weight was 235 mg / cm 2 and pressed at a pressure of 1.4 MPa for about 10 seconds to prepare a positive electrode for a lithium ion battery (16.2 cm × 16.2 cm) with a thickness of 1 mm of a positive electrode active material layer in which the positive electrode slurry was crimped.

[0166] (Examples 17 to 21, Comparative Examples 9 to 11) Positive electrodes of Examples 17 to 21 and Comparative Examples 9 to 11 were prepared in the same manner as in Example 16, except that coated positive electrode active material particles P-2 to P-6 or coated positive electrode active material particles P'-1 to P'-3 were used instead of the coated positive electrode active material particles P-1.

[0167] (Measurement of electrode angle, disintegration volume, defect rate and surface roughness) The fabricated electrode was cut into a size of 19×11×1 mm. Using a one-shot 3D shape measuring machine "VR-3200" (manufactured by Keyence), the image of the electrode piece after cutting was acquired at a magnification of 12 times. Note that although the thickness of the electrode piece of the above size is 1 mm, this means that the thickness of only the positive electrode active material layer is 1 mm. Using the one-shot 3D shape measuring machine "VR-3200" (manufactured by Keyence), the electrode angle, collapse volume, defect rate, and surface roughness were measured by the following methods. The results are shown in Table 3.

[0168] Among the cross-sections of the positive electrode active material layer, the average value of the angles of the corners in contact with the current collector was measured as the electrode angle. Compared with a rectangular parallelepiped of size 19×11×1 mm, the volume of the part where the positive electrode active material layer was chipped off in the electrode piece after cutting was measured as the collapse volume. The percentage of the collapse volume with respect to the volume of the rectangular parallelepiped of size 19×11×1 mm (209 mm 3 ) was calculated as the defect rate. Among the surfaces of the positive electrode active material layer, the arithmetic mean roughness Ra measured in accordance with JIS-B0601:2001 was measured by the one-shot 3D shape measuring machine "VR-3200" (manufactured by Keyence) as the surface roughness of the surface opposite to the surface in contact with the current collector.

[0169]

Table 3

[0170] The larger the electrode angle, the less the electrode defect, which means excellent formability. The smaller the value of the defect rate, the less the electrode defect, which means excellent formability. The smaller the value of the surface roughness, the smoother the surface of the electrode. As shown in Table 3, the positive electrode of the example was excellent in formability (low defect rate) and had a smooth surface.

[0171] [Fabrication of negative electrode] (Fabrication of resin current collector for negative electrode) Using a twin-screw extruder, 28 parts of block polypropylene [polyolefin resin, trade name "Sun Allomer PC684S", manufactured by Sun Allomer Co., Ltd.], 67 parts of nickel powder [conductive filler, nickel powder Type255, manufactured by Vale Japan Co., Ltd.] and 5 parts of dispersant [trade name "Yumex 1001", manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200 °C and 200 rpm to obtain a conductive resin composition for the negative electrode used for the first resin current collector layer. Using a twin-screw extruder, 28 parts of block polypropylene [polyolefin resin, trade name "Sun Allomer PC684S", manufactured by Sun Allomer Co., Ltd.], 67 parts of carbon nanotubes [conductive filler, trade name: "FloTube9000", manufactured by CNano] and 5 parts of dispersant [trade name "Yumex 1001", manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200 °C and 200 rpm to obtain a conductive resin composition for the negative electrode used for the second resin current collector layer. The conductive resin composition for the negative electrode used for the obtained first resin current collector layer and the conductive resin composition for the negative electrode used for the second resin current collector layer were passed through a co-extrusion film forming machine and stretched and rolled to obtain a conductive film for the resin current collector for the negative electrode provided with a first resin current collector layer having a film thickness of 50 μm and a second resin current collector layer having a film thickness of 50 μm. Next, the obtained conductive film for the resin current collector for the negative electrode was cut to a size of 17.0 cm × 17.0 cm, nickel vapor deposition was performed on one side (the surface of the first resin current collector layer), and a negative electrode resin current collector (N-1) connected with a terminal for current extraction (5 mm × 3 cm) was produced.

[0172] (Example 22) 150 parts of the above electrolytic solution and 4.2 parts of carbon fiber [Donacarb Mild S-243 manufactured by Osaka Gas Chemical Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS / cm] were mixed at 2000 rpm for 5 minutes using a planetary stirring type mixing and kneading device {Avatori Rentaro [manufactured by Shinchi Co., Ltd.]}. Subsequently, after adding 50 parts of the above electrolytic solution and 206 parts of the above coated negative electrode active material particles N-1, it was further mixed at 2000 rpm for 2 minutes using Avatori Rentaro, and 20 parts of the above electrolytic solution were further added. Subsequently, agitation was performed by Awatari Rentaro at 2000 rpm for 1 minute, and after further adding 2.3 parts of the above electrolytic solution, agitation was performed by Awatari Rentaro at 2000 rpm for 2 minutes to mix, and a negative electrode slurry was prepared. The obtained negative electrode slurry was applied to one side (the surface of the first resin current collector layer) of the negative electrode resin current collector so that the mass per unit area of the active material was 90 mg / cm 2 and pressed at a pressure of 1.4 MPa for about 10 seconds to produce a negative electrode for a lithium-ion battery (16.2 cm × 16.2 cm) with a thickness of 1 mm of a negative electrode active material layer in which the negative electrode slurry was pressure-bonded.

[0173] (Examples 23 to 30, Comparative Examples 12 to 16) Negative electrodes of Examples 23 to 30 and Comparative Examples 12 to 16 were produced in the same manner as in Example 22, except that coated negative electrode active material particles N-2 to N-9 or coated negative electrode active material particles N'-1 to N'-5 were used instead of the coated negative electrode active material particles N-1.

[0174] The produced electrode was cut into a size of 19 × 11 × 1 mm. Using a one-shot 3D shape measuring machine "VR-3200" (manufactured by Keyence), an image of the electrode piece after cutting was acquired at a magnification of 12 times. Note that the electrode piece of the above size has a thickness of 1 mm, which means that only the thickness of the negative electrode active material layer is 1 mm. Using a one-shot 3D shape measuring machine "VR-3200" (manufactured by Keyence), the electrode angle, disintegration volume, defect rate, and surface roughness were measured in the same manner as for the positive electrode. The results are shown in Table 4.

[0175] [Table 4]

[0176] As shown in Table 4, the negative electrodes of the examples were excellent in formability (low defect rate) and had a smooth surface.

[0177] [Fabrication of Lithium-Ion Single Battery for Positive Electrode Evaluation] (Example 31) A positive electrode for manufacturing a lithium-ion battery used in Example 31 was fabricated in the same manner as in Example 16, except that the basis weight of the positive electrode slurry was 100 mg and the thickness of the positive electrode active material layer was 420 μm. A lithium-ion single battery for positive electrode evaluation according to Example 31 was fabricated by combining the above positive electrode for manufacturing a lithium-ion battery and a negative electrode for manufacturing a lithium-ion battery (negative electrode containing coated negative electrode active material particles N-7) used in Example 43 described later via a separator (Celgard #3501).

[0178] [Fabrication of Lithium-Ion Battery Module for Positive Electrode Evaluation] Two lithium-ion single batteries according to Example 31 were stacked such that the positive electrode current collector of one single battery and the negative electrode current collector of the other single battery overlapped, and they were sandwiched between two commercially available heat-sealable aluminum laminate films. Three sides of the outer periphery of the aluminum laminate film were heat-sealed, and the remaining one side was vacuum-sealed and adhered to obtain a lithium-ion battery module for positive electrode evaluation according to Example 31.

[0179] (Examples 32 to 36, Comparative Examples 17 to 19) The basis weight of the slurry for the positive electrode was 100 mg / cm 2 and a positive electrode for manufacturing a lithium-ion battery used in Examples 32 to 36 and Comparative Examples 17 to 19 was fabricated in the same manner as in Examples 17 to 21 or Comparative Examples 9 to 11, except that the thickness of the positive electrode active material layer was 420 μm. A lithium-ion single battery for positive electrode evaluation and a lithium-ion battery module for positive electrode evaluation according to Examples 32 to 36 and Comparative Examples 17 to 19 were fabricated in the same manner as in Example 31, except that the above positive electrode for manufacturing a lithium-ion battery was used.

[0180] [Measurement of Discharge Capacity Retention Rate (50 Cycles)] (Cycle Test) Regarding the lithium-ion batteries for positive electrode evaluation and the lithium-ion battery modules for positive electrode evaluation manufactured in each example and comparative example, at 25°C, using a charge-discharge measurement device "Battery Analyzer 1470 type" [manufactured by Toyo Technica Co., Ltd.], they were charged to 4.2V at a current of 0.1C, and after a 10-minute rest, discharged to 2.5V at a current of 0.1C, and this charge-discharge cycle was repeated 50 times.

[0181] (Measurement of DC resistance value (DCR)) Regarding the lithium-ion batteries for positive electrode evaluation and the lithium-ion battery modules for positive electrode evaluation used in the measurement of discharge capacity retention rate, the DC resistance value at the first cycle (initial DCR) and the DC resistance value after 50 cycles (DCR (50 cycles)) were measured. The initial DCR was calculated from the voltage drop during the first 10 seconds from the start of discharge in the first cycle, and the 50-cycle DCR was calculated from the voltage drop during the first 10 seconds from the start of discharge in the 50th cycle. The results are shown in Table 5.

[0182] (Measurement of discharge capacity retention rate) The battery capacity at the first charge during the cycle test (initial discharge capacity) and the battery capacity at the 50th charge (discharge capacity retention rate (50 cycles)) were measured. The discharge capacity retention rate was calculated from the following formula. The results are shown in Table 5. Note that the larger the numerical value, the less the battery deterioration. Discharge capacity retention rate (%) = (Discharge capacity at the 50th cycle / Discharge capacity at the first cycle) × 100

[0183]

Table 5

[0184] As shown in Table 5, the lithium-ion single cells for positive electrode evaluation and the lithium-ion battery modules for positive electrode evaluation in the examples had a high discharge capacity retention rate (50 cycles) and less battery deterioration.

[0185] [Fabrication of lithium-ion single cells for negative electrode evaluation] (Example 37) The basis weight of the negative electrode slurry was 48 mg / cm2 A negative electrode for manufacturing a lithium-ion battery used in Example 37 was produced in the same manner as in Example 22, except that the thickness of the negative electrode active material layer was set to 580 μm. The negative electrode for manufacturing a lithium-ion battery and the positive electrode for manufacturing a lithium-ion battery used in Example 32 (a positive electrode containing coated positive electrode active material particles P-2) were combined via a separator (Celgard #3501) to produce a lithium-ion single battery for negative electrode evaluation according to Example 37.

[0186] [Fabrication of Lithium-Ion Battery Module for Negative Electrode Evaluation] Two lithium-ion single batteries according to Example 37 were stacked such that the positive electrode current collector of one single battery and the negative electrode current collector of the other single battery overlapped, and the stack was sandwiched between two commercially available heat-sealable aluminum laminate films. Three sides of the outer periphery of the aluminum laminate film were heat-sealed, and the remaining one side was vacuum-sealed and adhered to obtain a lithium-ion battery module for negative electrode evaluation according to Example 37.

[0187] (Examples 38 to 45, Comparative Examples 20 to 24) The basis weight of the slurry for the negative electrode was 48 mg / cm 2 A negative electrode for manufacturing a lithium-ion battery used in Examples 38 to 45 and Comparative Examples 20 to 24 was produced in the same manner as in Examples 23 to 30 or Comparative Examples 12 to 16, except that the thickness of the negative electrode active material layer was set to 580 μm. A lithium-ion single battery for negative electrode evaluation and a lithium-ion battery module for negative electrode evaluation according to Examples 38 to 45 and Comparative Examples 20 to 24 were produced in the same manner as in Example 37, except that the negative electrode for manufacturing a lithium-ion battery described above was used.

[0188] (Cycle Test) For the lithium-ion batteries for negative electrode evaluation and the lithium-ion battery modules for negative electrode evaluation manufactured in each Example and Comparative Example, the initial DCR, DCR (50 cycles), and discharge capacity retention rate (50 cycles) were measured in the same manner as for the lithium-ion single batteries for positive electrode evaluation and the lithium-ion battery modules for positive electrode evaluation. The results are shown in Table 6.

[0189]

Table 6

[0190] As shown in Table 6, the lithium-ion single battery for negative electrode evaluation and the lithium-ion battery module for negative electrode evaluation in the examples had a high discharge capacity retention rate (50 cycles) and little battery deterioration.

Industrial Applicability

[0191] The coated electrode active material particles for a lithium-ion battery of the present invention are particularly useful as coated electrode active material particles for a lithium-ion battery used for mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims

1. A coated electrode active material particle for a lithium-ion battery, wherein at least a part of the surface of the electrode active material particle is coated with a coating layer containing a polymer compound and a conductive assistant, and the Carr's flowability index is 55 to 65.

2. The coated electrode active material particle for a lithium-ion battery according to Claim 1, wherein the internal friction angle is 38.9° or more.

3. The coated electrode active material particle for a lithium-ion battery according to Claim 1, wherein the shear adhesion force of a powder layer composed of the coated electrode active material particle for a lithium-ion battery at a vertical pressure of 20 kPa in a shear test based on JIS-Z8835 is 620 Pa or more.

4. The average envelope area is 30 μm ２ The coated electrode active material particles for a lithium ion battery according to claim 1, wherein the average envelope area is 30 μm or less, and / or the average envelope perimeter is 20 μm or less.

5. An electrode for a lithium-ion battery comprising the coated electrode active material particle for a lithium-ion battery according to any one of Claims 1 to 4.

6. A lithium-ion single cell comprising the electrode for a lithium-ion battery according to Claim 5.

7. A battery module in which a plurality of the lithium-ion single cells according to Claim 6 are stacked.

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