JP6436101B2 - Electrode for electrochemical element and electrochemical element - Google Patents

Description

  The present invention relates to an electrode for an electrochemical element and an electrochemical element.

  Electrochemical elements such as lithium ion secondary batteries that are small and lightweight, have high energy density, and can be repeatedly charged and discharged are rapidly expanding their demands by taking advantage of their characteristics. Lithium ion secondary batteries are used in fields such as mobile phones, notebook personal computers, and electric vehicles because of their relatively high energy density.

  With the expansion and development of applications, these electrochemical elements are required to be further improved, such as lowering resistance, increasing capacity, improving mechanical properties and productivity. Under such circumstances, there is a demand for a more productive manufacturing method for electrochemical element electrodes, and various improvements have been made regarding the manufacturing method capable of high-speed molding and the materials for electrochemical element electrodes suitable for the manufacturing method. Has been done.

  An electrode for an electrochemical element is usually formed by laminating an electrode active material layer formed by binding an electrode active material and a conductive material used as necessary with a binder on a current collector. is there. In addition, an intermediate layer such as an adhesive layer for improving adhesion and a rust prevention layer for rust prevention is also provided between the electrode active material layer and the current collector.

  For example, Patent Document 1 discloses that a current collector made of copper that has been subjected to roughening treatment is subjected to rust prevention treatment, and then an electrode active material layer is formed using a slurry containing a negative electrode active material and a binder. .

  Patent Document 2 discloses that a conductive coating film formed by a conductive coating solution containing a polymer having a hydroxyl group and / or an amino acid and a conductive filler is formed on a current collector, and then an electrode active material and It is disclosed that an electrode active material layer is formed using a slurry containing a binder.

Japanese Patent No. 5090028 Japanese Patent No. 5134939

However, the electrode for an electrochemical element described in Patent Document 1 does not have sufficient adhesion between the current collector and the electrode active material layer. In addition, the electrochemical device including the electrode for an electrochemical device described in Patent Document 2 has not been sufficiently durable.
An object of the present invention is to provide an electrode for an electrochemical element and an electrochemical element that are excellent in adhesion between a current collector and an electrode active material layer and that are excellent in durability.

  As a result of intensive studies, the present inventor has found that the above object can be achieved by specifying a specific combination of the material contained in the intermediate layer and the composition of the binder contained in the electrode active material layer. It came to be completed.

That is, according to the present invention,
(1) An electrode for an electrochemical element in which an electrode active material layer containing an electrode active material and a binder is formed on a current collector, and an anchor layer containing a cationic compound is provided on the current collector. The binder has an acid group-containing monomer unit in an amount of 0.1 to 10% by weight, and the binder content in the electrode active material layer is 0.1 to 20 parts by weight based on 100 parts by weight of the electrode active material. Electrode for an electrochemical element that is part by weight,
(2) The electrode for electrochemical devices according to (1), wherein the cationic compound has a number average molecular weight of 10,000 to 2,000,000.
(3) The electrode for an electrochemical element according to (1) or (2), wherein the anchor layer has a thickness of 0.01 μm or more and less than 1 μm.
(4) The electrode for an electrochemical element according to any one of (1) to (3), wherein the acid group-containing monomer unit includes any of a carboxyl group, a sulfonic acid group, and a phosphoric acid group,
(5) An electrochemical element comprising the electrode for an electrochemical element according to any one of (1) to (4), a separator, and an electrolytic solution,
(6) The electrochemical device according to (5), wherein the electrochemical device is a lithium ion secondary battery,
Is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for electrochemical elements and electrochemical element which were excellent in the adhesive force of a collector and an electrode active material layer, and also excellent in durability can be provided.

  Hereinafter, the electrode for an electrochemical element of the present invention will be described. The electrode for an electrochemical device of the present invention is an electrode for an electrochemical device in which an electrode active material layer containing an electrode active material and a binder is formed on a current collector, and the electrode for the electrochemical device is cationic on the current collector. An anchor layer containing a compound, the binder has an acid group-containing monomer unit in an amount of 0.1 to 10% by weight, and the binder content in the electrode active material layer is 100 parts by weight of the electrode active material; It is 0.1-20 weight part with respect to it.

(Electrodes for electrochemical devices)
The electrode for an electrochemical device of the present invention can be obtained by forming an anchor layer on a current collector and further forming an electrode active material layer on the current collector on which the anchor layer is formed.

The material of the current collector is, for example, metal, carbon, conductive polymer, etc., and metal is preferably used. As the current collector metal, aluminum, platinum, nickel, tantalum, titanium, stainless steel, copper, other alloys and the like are usually used. Among these, it is preferable to use copper, aluminum, or an aluminum alloy in terms of conductivity and voltage resistance.
The thickness of the current collector is preferably 5 to 100 μm, more preferably 8 to 70 μm, and still more preferably 10 to 50 μm.

(Anchor layer)
The electrode for an electrochemical element of the present invention includes an anchor layer. The anchor layer includes a cationic compound.

(Cationic compound)
As the cationic compound contained in the anchor layer, a primary amine compound, a secondary amine compound (imino group-containing compound), a tertiary amine compound, a compound modified with a cationizing agent, or the like can be used. Of these, an imino group-containing compound and a compound modified with a cationizing agent are preferable.

  An imino group-containing compound is a compound having an imino group, and the nitrogen atom of the imino group may be bonded to the same carbon atom by a double bond, or may be bonded to a separate carbon atom by a single bond. May be.

  As the imino group-containing compound, a low molecular imino group-containing compound or a high molecular imino group-containing compound may be used. Examples of the low molecular imino group-containing compound include chain imino group-containing compounds such as dimethylamine, diethylamine, and dipropylamine; cyclic imino group-containing compounds such as ethyleneimine, propyleneimine, pyrrolidine, piperidine, and piperazine. It is done. Examples of the polymer imino group-containing compound include polyethyleneimine; polyimineimine derivatives such as poly N-hydroxylethyleneimine and carboxymethylated polyethyleneimine / sodium salt; polypropyleneimine; polyN-2-dihydroxypropyleneimine And the like, and the like, and the like.

  Among these, a polymer imino group-containing compound is preferable, and polyethyleneimine is more preferable. Moreover, an imino group containing compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Examples of the compound modified with a cationizing agent include cationized cellulose and the like obtained by modifying a cellulose compound such as hydroxyethyl cellulose and carboxymethyl cellulose with a cationizing agent.
The number average molecular weight of the cationic compound is preferably 100 to 2,000,000, and more preferably 10,000 to 2,000,000.
The number average molecular weight of the cationic compound can be measured, for example, by gel permeation chromatography (GPC) using polystyrene as a standard substance.

  The method for forming the anchor layer is not particularly limited, but the anchor layer is formed by applying a coating solution for an anchor layer in which a cationic compound is dispersed or dissolved in a solvent such as water on a current collector and drying it. be able to. Further, the concentration can be appropriately adjusted according to the coating method of the cationic compound in the anchor layer coating solution.

  The method for applying the anchor layer coating solution is not particularly limited. For example, the anchor layer is formed on the current collector by a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a die coating method, a brush coating, or the like. Further, after forming an adhesive layer on the release paper, it may be transferred to a current collector.

  In addition, examples of the method for drying the anchor layer coating solution coated on the current collector include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. Can be mentioned. Of these, a drying method using hot air and a drying method using irradiation with far infrared rays are preferable. The drying temperature and the drying time are preferably a temperature and a time at which the solvent in the current collector coating adhesive coating solution coated on the current collector can be completely removed, and the drying temperature is usually 50 to 300 ° C., preferably 80 ~ 250 ° C. The drying time is usually 2 hours or less, preferably 5 seconds to 30 minutes.

  The thickness of the anchor layer is preferably 0.01 μm or more and less than 10 μm, more preferably 0.01 μm or more and 2 μm, from the viewpoint of obtaining an electrode having good adhesion to the electrode active material layer described later and low resistance. Less than, more preferably 0.01 μm or more and less than 1 μm.

(Electrode active material layer)
The electrode for an electrochemical element of the present invention includes an electrode active material layer, and the electrode active material layer includes an electrode active material, a binder, a thickener used as necessary, and a conductive additive. The binder content in the electrode active material layer is 0.1 to 20 parts by weight, preferably 0.2 to 15 parts by weight, more preferably 0.3 to 10 parts by weight, with respect to 100 parts by weight of the electrode active material. It is.

  The electrode active material layer is formed by applying and drying an electrode slurry containing an electrode active material, a binder, a thickener used as necessary, and a conductive auxiliary agent on the anchor layer of the current collector on which the anchor layer is formed. Is formed.

  The method for applying the electrode slurry onto the anchor layer formed on the current collector is not particularly limited. Examples thereof include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a comma direct coating, a slide die coating, and a brush coating method. Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 1 to 60 minutes, and the drying temperature is usually 40 to 180 ° C. The electrode active material layer may be formed by repeating application and drying of the electrode slurry a plurality of times.

  Here, the electrode slurry can be obtained by mixing an electrode active material, a binder, a thickener and a conductive aid used as necessary, and a solvent such as water.

  The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

(Electrode active material)
In the case where the electrochemical device is a lithium ion secondary battery, the electrode active material (positive electrode active material) of the positive electrode for the lithium ion secondary battery includes a metal oxide capable of reversibly doping and dedoping lithium ions. It is done. Examples of the metal oxide include lithium cobaltate, lithium nickelate, lithium manganate, and lithium iron phosphate. In addition, the positive electrode active material illustrated above may be used independently according to a use, and may be used in mixture of multiple types.

  As the negative electrode active material (negative electrode active material) as the counter electrode of the positive electrode for a lithium ion secondary battery, for example, low crystalline carbon (non-graphitizable carbon, non-graphitizable carbon, pyrolytic carbon, etc.) Crystalline carbon), graphite (natural graphite, artificial graphite), alloy materials such as tin and silicon, oxides such as silicon oxide, tin oxide, and lithium titanate. In addition, the negative electrode active material illustrated above may be used independently according to a use suitably, and multiple types may be mixed and used for it.

  The shape of the electrode active material of the electrode for a lithium ion secondary battery is preferably a granulated particle. When the shape of the particles is granular, a higher-density electrode can be formed during electrode molding.

  The volume average particle diameter of the electrode active material of the electrode for a lithium ion secondary battery is usually 0.1 to 100 μm, preferably 0.5 to 50 μm, more preferably 0.8 to 30 μm for both the positive electrode and the negative electrode.

  Examples of the negative electrode active material preferably used when the electrochemical element is a lithium ion capacitor include low crystalline carbon (amorphous carbon such as graphitizable carbon, non-graphitizable carbon, and pyrolytic carbon). ), Graphite (natural graphite, artificial graphite) and the like, and negative electrode active materials formed of carbon.

  In addition, as the positive electrode active material when the electrochemical element is a lithium ion capacitor, any material can be used as long as it can reversibly carry lithium ions and anions such as tetrafluoroborate. Specifically, an allotrope of carbon can be preferably used. Specific examples of the allotrope of carbon include activated carbon, polyacene (PAS), carbon whisker, carbon nanotube, and graphite.

(binder)
The binder used in the present invention is a component for adhering electrode active materials to each other, and is usually used in the form of a solution or dispersion in which polymer particles having binding properties are dissolved or dispersed in a solvent such as water.

  Examples of the binder used in the present invention include diene polymers and acrylic polymers.

(Diene polymer)
The diene polymer is a polymer containing monomer units obtained by polymerizing conjugated dienes such as butadiene and isoprene. The proportion of monomer units obtained by polymerizing conjugated diene in the diene polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. Examples of the polymer include homopolymers of conjugated dienes such as polybutadiene and polyisoprene; and copolymers of monomers that are copolymerizable with conjugated dienes. Examples of the copolymerizable monomer include α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid and methacrylic acid; styrene, chlorostyrene, vinyltoluene, and t-butyl. Styrene monomers such as styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinylbenzene; olefins such as ethylene, propylene; vinyl chloride, vinylidene chloride Halogen atom-containing monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, etc .; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; methyl vinyl ketone, ethyl vinyl Vinyl ketones such as ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole.

(Acrylic polymer)
The acrylic polymer is a polymer containing a monomer unit obtained by polymerizing an acrylic ester and / or a methacrylic ester. The proportion of monomer units obtained by polymerizing acrylic acid ester and / or methacrylic acid ester in the acrylic polymer is usually 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more. . Examples of the polymer include homopolymers of acrylic acid esters and / or methacrylic acid esters, and copolymers with monomers copolymerizable therewith. Examples of the copolymerizable monomer include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; two or more carbons such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate. -Carboxylic acid ester having a carbon double bond; styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, vinyl benzoate methyl, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, Styrene monomers such as divinylbenzene; Amide monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropane sulfonic acid; α, β-defect such as acrylonitrile and methacrylonitrile Nitrile compounds; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; monomers containing halogen atoms such as vinyl chloride and vinylidene chloride; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate Vinyl esters such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; N-vinyl pyrrolidone, vinyl Heterocycle-containing vinyl compounds such as pyridine and vinylimidazole can be mentioned.

  Among these, since it is excellent in adhesiveness, a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, and an acrylic polymer are preferable, and a styrene-butadiene copolymer and an acrylic polymer are more preferable.

(Acid group-containing monomer)
The binder used in the present invention further contains an acid group-containing monomer unit. Examples of the acid group-containing monomer that leads to the acid group-containing monomer unit include -COOH group (carboxyl group); -SO ₃ H group (sulfonic acid group); -PO ₃ H ₂ group and -PO (OH ) (OR) groups (wherein R represents a hydrocarbon group) or the like; monomers having an acid group such as;

  Examples of the monomer having a carboxyl group include monocarboxylic acids, dicarboxylic acids, dicarboxylic acid anhydrides, and derivatives thereof. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, crotonic acid, 2-ethylacrylic acid, and isocrotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and methylmaleic acid. Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride and the like.

  Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamide-2. -Methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, 2- (N-acryloyl) amino-2-methyl-1,3-propane-disulfonic acid and the like. In the present invention, “(meth) acryl” means “acryl” or “methacryl”.

Examples of the monomer having a phosphate group such as —PO ₃ H ₂ group and —PO (OH) (OR) group (R represents a hydrocarbon group) include, for example, phosphate-2- (meth) acryloyloxy phosphate Examples include ethyl, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (meth) acryloyloxyethyl phosphate. In the present invention, “(meth) acryloyl” means “acryloyl” or “methacryloyl”.
Moreover, the salt of the monomer mentioned above can also be used as an acid group-containing monomer.

  Moreover, an acid group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. For example, different types of monomers containing the same type of acidic group may be used in combination. Further, for example, monomers containing different types of acidic groups may be used in combination.

  The content of the acid group-containing monomer unit in the binder used in the present invention is 0.1 to 10% by weight, preferably 0.2 to 9% by weight, and more preferably 0.3 to 8% by weight.

(Thickener)
The electrode active material layer of the present invention may contain a thickener as necessary. Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. Among these, it is preferable to use carboxymethylcellulose, ammonium salt of carboxymethylcellulose, and alkali metal salt. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”.

  The content of the thickener in the electrode active material layer is preferably in a range that does not affect the battery characteristics, preferably 0.1 to 5 parts by weight, more preferably 0.2 to 100 parts by weight with respect to 100 parts by weight of the electrode active material. 4 parts by weight, more preferably 0.3 to 3 parts by weight.

(Conductive aid)
The electrode active material layer of the present invention may contain a conductive additive as necessary. The conductive auxiliary agent is not particularly limited as long as it is a conductive material, but a conductive particulate material is preferable. For example, conductive carbon black such as furnace black, acetylene black, and ketjen black; natural And graphite such as graphite and artificial graphite; and carbon fibers such as polyacrylonitrile-based carbon fiber, pitch-based carbon fiber, and vapor grown carbon fiber. The average particle diameter when the conductive assistant is a particulate material is not particularly limited, but is preferably smaller than the average particle diameter of the electrode active material, from the viewpoint of expressing sufficient conductivity with a smaller amount of use. The thickness is preferably 0.001 to 10 μm, more preferably 0.05 to 5 μm, and still more preferably 0.1 to 1 μm.

(Electrochemical element)
Examples of usage of the electrode for an electrochemical element of the present invention include a lithium ion secondary battery and a lithium ion capacitor using such an electrode, and a lithium ion secondary battery is preferable. For example, a lithium ion secondary battery uses an electrode for an electrochemical element obtained as described above as at least one of a positive electrode and a negative electrode, and further includes a separator and an electrolytic solution.

  As the separator, for example, a polyolefin resin such as polyethylene or polypropylene, or a microporous film or nonwoven fabric containing an aromatic polyamide resin; a porous resin coat containing an inorganic ceramic powder;

  The thickness of the separator is preferably 0.5 to 40 μm, more preferably from the viewpoint of reducing resistance due to the separator in the lithium ion secondary battery and excellent workability when manufacturing the lithium ion secondary battery. It is 1-30 micrometers, More preferably, it is 1-25 micrometers.

(Electrolyte)
The electrolytic solution is not particularly limited. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. These can be used alone or in admixture of two or more. The amount of the supporting electrolyte is usually 1 wt. % Or more, preferably 5 wt. % Or more, and usually 30 wt. % Or less, preferably 20 wt. % Or less. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the battery are degraded.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Usually, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfolane and dimethyl sulfoxide Sulfur-containing compounds are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used alone or in admixture of two or more. Moreover, it is also possible to use an electrolyte containing an additive. The additive is preferably a carbonate compound such as vinylene carbonate (VC).

Examples of the electrolytic solution other than the above include a gel polymer electrolyte in which a polymer electrolyte such as polyethylene oxide and polyacrylonitrile is impregnated with the electrolytic solution, lithium sulfide, LiI, Li ₃ N, Li ₂ S—P ₂ S ₅ glass ceramic, etc. An inorganic solid electrolyte can be mentioned.

  A lithium ion secondary battery is obtained by stacking a negative electrode and a positive electrode through a separator, winding this according to the shape of the battery, folding it into a battery container, pouring the electrolyte into the battery container and sealing it. It is done. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode for electrochemical elements and electrochemical element which were excellent in the adhesive force of a collector and an electrode active material layer, and also excellent in durability can be provided.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily changed without departing from the gist and equivalent scope of the present invention. Can be implemented. In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified.

  In Examples and Comparative Examples, adhesion, durability, and low temperature characteristics were evaluated as follows.

(1) Adhesiveness (1-1) Peel strength The electrodes for lithium ion secondary batteries produced in Examples and Comparative Examples were cut into rectangles having a length of 100 mm and a width of 10 mm to form test pieces, with the electrode active material layer surface facing down. Measure the stress when cellophane tape (as defined in JIS Z1522) is applied to the surface of the electrode active material layer, and one end of the current collector having the anchor layer is pulled in the vertical direction at a pulling speed of 50 mm / min. (The cellophane tape is fixed to the test stand.) The measurement was performed three times, the average value was obtained and this was taken as the peel strength, and the results are shown in Tables 1 and 2. The higher the peel strength, the greater the binding force of the electrode active material layer to the anchor layer, that is, the higher the adhesion strength.

(2) Durability (2-1) Peel strength after measurement of high-temperature cycle characteristics After evaluation of (2-2), the lithium ion secondary battery of an 800 mAh wound cell was disassembled and vacuumed at 60 ° C. for 24 hours. Dried. Thereafter, the electrode for the lithium ion secondary battery is cut into a rectangle having a length of 100 mm and a width of 10 mm to obtain a test piece, and a cellophane tape (as defined in JIS Z1522) is formed on the surface of the electrode active material layer with the electrode active material layer side down. The one end of the current collector having the anchor layer was pulled in the vertical direction and pulled at a pulling speed of 50 mm / min, and the stress was measured (note that the cellophane tape was fixed to the test stand). The measurement was performed three times, the average value was obtained and this was taken as the peel strength, and the results are shown in Tables 1 and 2. The higher the peel strength, the greater the binding force of the electrode active material layer to the anchor layer, that is, the higher the adhesion strength.

(2-2) High-temperature cycle characteristics After the lithium-ion secondary battery of the 800 mAh wound-type cell produced in Examples and Comparative Examples was allowed to stand for 24 hours in an environment at 25 ° C, Charge / discharge operation was performed by charging at 4.2 V and 0.1 C and discharging at 3.0 V and 0.1 C, and the initial capacity C ₀ was measured. Furthermore, charging / discharging was repeated under an environment of 60 ° C., and the capacity C ₁ after 1000 cycles was measured. The high-temperature cycle characteristics were evaluated by the capacity retention rate represented by ΔC = C ₁ / C ₀ × 100 (%), and the results are shown in Tables 1 and 2. It shows that it is excellent in a lifetime characteristic, so that this value is high.

(2-3) Cell volume change before and after the cycle After allowing the lithium ion secondary battery of the 800 mAh wound-type cell produced in the examples and comparative examples to stand in an environment of 25 ° C. for 24 hours, Under the environment, after charging / discharging operation by charging at 4.2V, 0.1C, discharging at 3.0V, 0.1C, the wound type cell was immersed in liquid paraffin, and the volume V ₀ was set. It was measured. Furthermore, charging and discharging were repeated under an environment of 60 ° C., the wound cell after 1000 cycles was immersed in liquid paraffin, and its volume V ₁ was measured. The cell volume change ΔV (%) before and after the high-temperature cycle characteristics was evaluated at (V ₁ −V ₀ ) / V ₀ × 100, and the results are shown in Tables 1 and 2. It shows that it is excellent in gas generation | occurrence | production suppression, so that this value is small.

(3) Low temperature characteristics (3-1) Low temperature output characteristics The 800 mAh wound type lithium ion secondary battery produced in the examples and comparative examples was allowed to stand for 24 hours in an environment of 25 ° C, Under the environment, 4.2 V, 0.1 C, and 5 hours of charging were performed, and the voltage V ₀ at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., and the voltage V ₁ 15 seconds after the start of discharge was measured. The low temperature characteristics were evaluated by a voltage change represented by ΔV = V ₀ −V ₁ , and the results are shown in Tables 1 and 2. It shows that it is excellent in a low temperature characteristic, so that this value is small.

  Moreover, the number average molecular weight of the cationic compound used in the Examples and Comparative Examples was measured by the following method.

(Measurement of number average molecular weight)
The cationic compound was dissolved in dimethylformamide to prepare a 1% solution. Using this as a measurement sample, GPC measurement was performed using polystyrene as a standard substance, and using a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide as a developing solvent.
The GPC measuring device is HLC-8220GPC (manufactured by Tosoh Corporation), the detector is HLC-8320GPC RI detector (manufactured by Tosoh Corporation), and the measuring column is TSKgel SuperHZM-M (manufactured by Tosoh Corporation). Measurement was performed at 40 ° C., a developing solvent flow rate of 0.6 mL / min, and a sample injection amount of 20 μl.

Example 1
(Manufacture of anchor layer)
Polyethyleneimine (Epomin, Nippon Shokubai Co., Ltd., number average molecular weight 700,000, 30% solid content aqueous solution) is discharged from a die onto a 12 μm thick copper current collector as a cationic compound, at a molding speed of 30 m / min. The current collector was applied on one side and dried at 120 ° C. for 5 minutes to form an anchor layer having a thickness of 0.5 μm.

(Manufacture of binder for negative electrode)
In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene (hereinafter sometimes referred to as “BD”), 3.5 parts of itaconic acid, and 62.5 of styrene (hereinafter sometimes referred to as “ST”). 1 part, 2-hydroxyethyl acrylate (hereinafter sometimes referred to as “β-HEA”), 0.4 part sodium dodecylbenzenesulfonate as an emulsifier, 150 parts ion-exchanged water, and potassium persulfate as a polymerization initiator 0 .5 parts was added, and after sufficiently stirring, the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion reached 96%, the reaction was stopped by cooling to obtain a mixture containing particulate negative electrode binder (styrene-butadiene copolymer (SBR)). After adding 5% aqueous sodium hydroxide solution to the mixture containing the particulate negative electrode binder and adjusting to pH 8, the unreacted monomer is removed by heating under reduced pressure, and then cooled to 30 ° C or lower. An aqueous dispersion containing the desired particulate negative electrode binder was obtained.

(Manufacture of negative electrode slurry)
Artificial graphite (average particle diameter: 15.6 μm) 100 parts, 2% aqueous solution of carboxymethyl cellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd .; hereinafter sometimes referred to as “CMC-Na salt”) as a thickener. The solid content was 1 part, and the solid content concentration was adjusted to 68% with ion-exchanged water, followed by mixing at 25 ° C. for 60 minutes. Further, the solid content was adjusted to 62% with ion-exchanged water, and further mixed at 25 ° C. for 15 minutes. In the mixed solution, 1.5 parts of the particulate negative electrode binder in an amount corresponding to the solid content and ion-exchanged water were added, adjusted to a final solid content concentration of 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry having good fluidity.

(Manufacture of negative electrodes for lithium ion secondary batteries)
On the copper current collector having the anchor layer, the negative electrode slurry obtained above was applied with a comma coater so that the film thickness after drying was about 150 μm, and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material before pressing. The negative electrode original fabric before pressing was rolled with a roll press to obtain a negative electrode for a lithium ion secondary battery after pressing (hereinafter, also referred to as “negative electrode”) having a negative electrode composition layer thickness of 80 μm.

(Production of slurry for positive electrode and positive electrode for lithium ion secondary battery)
92 parts of LiCoO ₂ (hereinafter sometimes referred to as “LCO”) as the positive electrode active material and 2 parts of solid content of polyvinylidene fluoride (PVDF; “KF-1100” manufactured by Kureha Chemical Co., Ltd.) as the binder for the positive electrode In addition, 6 parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) and 20 parts of N-methylpyrrolidone were added and mixed with a planetary mixer to obtain a slurry for a positive electrode. This positive electrode slurry is applied to an aluminum foil having a thickness of 18 μm, dried at 120 ° C. for 30 minutes, and then roll-pressed to form a positive electrode for a lithium ion secondary battery having a thickness of 60 μm (hereinafter, referred to as “positive electrode”). )

(Preparation of separator)
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by dry method, porosity 55%) was cut out to 55 × 5.5 cm ² .

(Manufacture of lithium ion secondary batteries)
Cut out positive electrode after pressing obtained above in 49 × 5 cm ^2, were placed separator was cut into 55 × 5.5cm ² thereon. Furthermore, the obtained negative electrode after pressing was cut out to 50 × 5.2 cm ² , and this was arranged on the separator so that the surface on the negative electrode active material layer side faces the separator. This was wound with a winding machine to obtain a wound body. The wound body is pressed at 60 ° C. and 0.5 MPa to form a flat body, and is wrapped with an aluminum packaging exterior as a battery exterior, and an electrolytic solution (solvent: EC / DEC / VC = 68.5 / 30/1. 5 volume ratio, electrolyte: 1M LiPF ₆ ) was injected so as not to leave air, and in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and 800 mAh A wound type lithium ion secondary battery was manufactured.

(Example 2)
Production of anchor layer, production of negative electrode slurry, production of negative electrode in the same manner as in Example 1 except that the amount of itaconic acid was 0.2 parts and the amount of styrene was 63.8 parts in the production of the negative electrode binder. And the lithium ion secondary battery was manufactured.

Example 3
In the production of the negative electrode binder, the anchor layer was produced in the same manner as in Example 1 except that the amount of 1,3-butadiene was 30 parts, the amount of itaconic acid was 9.5 parts, and the amount of styrene was 59.5 parts. The production of slurry for negative electrode, the production of negative electrode and the production of lithium ion secondary battery were carried out.

(Example 4)
In the production of the negative electrode slurry, the production of the anchor layer, the production of the negative electrode, and the lithium ion secondary were the same as in Example 1 except that the amount of the particulate negative electrode binder used was 0.2 parts in terms of solid content. The battery was manufactured.

(Example 5)
In the production of the negative electrode slurry, the anchor layer, the negative electrode, and the lithium ion secondary battery were produced in the same manner as in Example 1 except that the amount of the particulate binder was 18 parts in terms of solid content. .

(Example 6)
In the production of the negative electrode binder, in the same manner as in Example 1, except that sodium styrenesulfonate (hereinafter sometimes referred to as “NaSS”) was used instead of itaconic acid, production of the anchor layer and production of the negative electrode slurry were performed. The negative electrode and the lithium ion secondary battery were manufactured.

(Example 7)
In the production of the negative electrode binder, except that methyl-2-methacryloyloxyethyl phosphate was used instead of itaconic acid, the production of the anchor layer, the production of the negative electrode slurry, the production of the negative electrode, and lithium were performed in the same manner as in Example 1. An ion secondary battery was manufactured.

(Example 8)
In the production of the anchor layer, as in Example 1, except that carboxymethylated polyethyleneimine sodium salt (number average molecular weight 50000, solid content concentration 3% aqueous solution) was used as the cationic compound instead of polyethyleneimine. Production of a slurry, production of a negative electrode, and production of a lithium ion secondary battery were performed.

Example 9
In the production of the anchor layer, as in Example 1, except that cationized cellulose (poise C-60H, number average molecular weight 600000, solid content concentration 3% aqueous solution) was used as the cationic compound instead of polyethyleneimine. Production of a slurry, production of a negative electrode, and production of a lithium ion secondary battery were performed.

(Example 10)
(Manufacture of anchor layer)
Polyethyleneimine (epomine, manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 700,000, 30% solid content aqueous solution) is discharged from a die onto an aluminum current collector having a thickness of 18 μm as a cationic compound, and at a molding speed of 30 m / min. The current collector was applied on one side and dried at 120 ° C. for 5 minutes to form an anchor layer having a thickness of 0.5 μm.

(Manufacture of binder for positive electrode)
In a 5 MPa pressure vessel with a stirrer, 76 parts of 2-ethylhexyl acrylate (hereinafter sometimes referred to as “2-EHA”), 4.0 parts of itaconic acid, and 20 parts of acrylonitrile (hereinafter sometimes referred to as “AN”). Then, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator were stirred sufficiently, and then heated to 50 ° C. to initiate polymerization. . When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing particulate positive electrode binder (acrylic polymer (ACL)). After adding 5% aqueous sodium hydroxide solution to the mixture containing the particulate positive electrode binder and adjusting the pH to 8, the unreacted monomer is removed by heating under reduced pressure, and then cooled to 30 ° C or lower. Thus, an aqueous dispersion containing a desired positive electrode binder was obtained.

(Production of positive electrode slurry)
To a planetary mixer with a disper, add 100 parts of LCO as a positive electrode active material, 1 part of a 2% aqueous solution of CMC-Na salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a viscosity-imparting agent. After adjusting the solid content concentration to 60% with exchange water, the mixture was mixed at 25 ° C. for 60 minutes. Next, after adjusting to 57% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC, and the liquid mixture was obtained.

  3 parts of the positive electrode binder (based on solid content) produced above and ion-exchanged water were added to the mixed solution, adjusted to a final solid content concentration of 54%, and mixed for another 10 minutes. This was defoamed under reduced pressure to obtain a positive electrode slurry having good fluidity.

  The positive electrode slurry was applied onto the aluminum current collector having the anchor layer with a comma coater so that the film thickness after drying was about 150 μm, and dried. This drying was performed by transporting the aluminum foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the positive electrode. The positive electrode raw material before pressing was rolled by a roll press to obtain a positive electrode after pressing with a positive electrode active material layer having a thickness of 80 μm.

(Manufacture of negative electrode slurry and lithium ion secondary battery negative electrode)
Artificial graphite as the negative electrode active material (average particle size: 24.5 μm, graphite interlayer distance ((002) plane spacing (d value): 0.354 nm by X-ray diffraction method) 96 parts, styrene-butadiene copolymer latex ( BM-400B) is 3.0 parts in terms of solid content, and 1.5 parts of a carboxymethylcellulose 1.5% aqueous solution (DN-800H: manufactured by Daicel Chemical Industries) as a dispersant is mixed in 1.0 part in terms of solid content. Further, ion exchange water was added so as to have a solid content concentration of 50%, and mixed and dispersed to obtain a negative electrode slurry, which was applied to a copper foil having a thickness of 18 μm and dried at 120 ° C. for 30 minutes. Thereafter, roll pressing was performed to obtain a negative electrode having a thickness of 50 μm.

(Preparation of separator)
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by dry method, porosity 55%) was cut out to 55 × 5.5 cm ² .

(Manufacture of lithium ion secondary batteries)
Cut out positive electrode after pressing obtained above in 49 × 5 cm ^2, were placed separator was cut into 55 × 5.5cm ² thereon. Furthermore, the obtained negative electrode after pressing was cut out to 50 × 5.2 cm ² , and this was arranged on the separator so that the surface on the negative electrode active material layer side faces the separator. This was wound with a winding machine to obtain a wound body. The wound body is pressed at 60 ° C. and 0.5 MPa to form a flat body, and is wrapped with an aluminum packaging exterior as a battery exterior, and an electrolytic solution (solvent: EC / DEC / VC = 68.5 / 30/1. 5 volume ratio, electrolyte: 1M LiPF ₆ ) was injected so as not to leave air, and in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and 800 mAh A wound type lithium ion secondary battery was manufactured.

(Comparative Example 1)
In the production of the negative electrode binder, the anchor layer was produced in the same manner as in Example 1, except that the amount of 1,3-butadiene was 30 parts, the amount of itaconic acid was 11.0 parts, and the amount of styrene was 58 parts. Slurry production, negative electrode production and lithium ion secondary battery production were carried out.

(Comparative Example 2)
In the production of the negative electrode slurry, the production of the anchor layer, the production of the negative electrode, and the lithium ion secondary battery was the same as in Example 1 except that the amount of the particulate negative electrode binder used was 22 parts in terms of solid content. Manufactured.

(Comparative Example 3)
In the production of the negative electrode binder, the amount of 1,3-butadiene was 30 parts, the amount of itaconic acid was 11.0 parts, and the amount of styrene was 58 parts. An anchor layer, a negative electrode, and a lithium ion secondary battery were manufactured in the same manner as in Example 1 except that the amount was 22 parts in terms of solid content.

(Comparative Example 4)
In the production of the binder for the negative electrode, the anchor layer was produced in the same manner as in Example 1, except that itaconic acid was not used and the amount of 1,3-butadiene was 34 parts and the amount of styrene was 65 parts. , Negative electrode, and lithium ion secondary battery.

(Comparative Example 5)
In the production of the anchor layer, except for using polyacrylic acid sodium salt without using a cationic compound, the production of the slurry for the negative electrode, the production of the negative electrode, and the production of the lithium ion secondary battery were performed in the same manner as in Example 1. It was.

(Comparative Example 6)
(Manufacture of anchor layer)
100 parts of carbon material (graphite / carbon black = 80/20) as a conductive filler is added to an aqueous solution in which 5 parts of a dispersant (polyvinyl alcohol) is dissolved in 80 parts of ion-exchanged water, and polyethylene is added as a cationic compound. An anchor layer slurry was prepared by adding 2 parts of imine (epomine, manufactured by Nippon Shokubai Co., Ltd., number average molecular weight 700,000, solid content concentration 30% aqueous solution) in an amount equivalent to solid content. The anchor layer slurry was discharged from a die onto a 12 μm thick copper current collector, applied to one side of the current collector at a molding speed of 30 m / min, and dried at 120 ° C. for 5 minutes to obtain a thickness of 0 An anchor layer of 0.5 μm was formed.
Except for using a copper current collector having an anchor layer containing the conductive filler, a negative electrode slurry, a negative electrode, and a lithium ion secondary battery were manufactured in the same manner as in Example 1.

(Comparative Example 7)
In the production of the anchor layer, except for forming the anchor layer having a thickness of 3 μm, the production of the slurry for the negative electrode, the production of the negative electrode, and the production of the lithium ion secondary battery were performed in the same manner as in Comparative Example 6.

  As shown in Tables 1 and 2, an electrode for an electrochemical device, in which an electrode active material layer containing an electrode active material and a binder is formed on a current collector, the cationic current on the current collector An anchor layer containing a compound, the binder has an acid group-containing monomer unit in an amount of 0.1 to 10% by weight, and the binder content in the electrode active material layer is 100 parts by weight of the electrode active material; On the other hand, the adhesion of the electrode for an electrochemical element, which is 0.1 to 20 parts by weight, was good, and the durability and low-temperature characteristics of a lithium ion secondary battery using this electrode for an electrochemical element were good. .

Claims (6)

An electrode for an electrochemical element in which an electrode active material layer containing an electrode active material and a binder is formed on a current collector,
On the current collector, having an anchor layer containing only a cationic compound,
The binder has an acid group-containing monomer unit in an amount of 0.1 to 10% by weight, and the content ratio of the binder in the electrode active material layer is 0.1 to 20 parts by weight with respect to 100 parts by weight of the electrode active material. An electrode for an electrochemical element.   The electrode for an electrochemical element according to claim 1, wherein the cationic compound has a number average molecular weight of 10,000 to 2,000,000.   The electrode for an electrochemical element according to claim 1 or 2, wherein the anchor layer has a thickness of 0.01 µm or more and less than 1 µm.   The electrode for electrochemical devices according to any one of claims 1 to 3, wherein the acid group-containing monomer unit includes any of a carboxyl group, a sulfonic acid group, and a phosphoric acid group.   The electrochemical element containing the electrode for electrochemical elements as described in any one of Claims 1-4, a separator, and electrolyte solution. The electrochemical device according to claim 5, wherein the electrochemical device is a lithium ion secondary battery.