JP6845733B2 - Manufacturing method of electrodes for lithium-ion batteries - Google Patents

Description

The present invention relates to a method for manufacturing an electrode for a lithium ion battery.

In recent years, there has been an urgent need to reduce carbon dioxide emissions for environmental protection. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of secondary batteries for driving motors, which holds the key to their practical application, is enthusiastic. It is done. As a secondary battery, attention is focused on a lithium ion battery that can achieve high energy density and high output density.

Patent Document 1 describes a battery characterized in that an active material having a small particle size can be held on the surface layer of the active material layer of the electrode, and the active material layer contains an adhesive material as an electrode having an enhanced electrode structure. Electrodes for use are described.

JP-A-2007-280806

In the battery electrode described in Patent Document 1, it is necessary to separately add an adhesive material in addition to the active material in order to maintain the shape of the electrode. However, the energy density of the electrode is lowered by the amount of the adhesive material remaining in the electrode.

The present invention has been made in view of the above problems, and the electrode is manufactured so that the shape of the electrode can be maintained without using the adhesive material remaining on the electrode and the energy density of the electrode is not lowered. It is an object of the present invention to provide a method for manufacturing an electrode for a lithium ion battery, which can be used.

The present inventors have arrived at the present invention as a result of diligent studies to solve the above problems.
That is, the present invention is for a lithium ion battery having an electrode active material layer containing a coated electrode active material having a coating layer containing a coating resin on at least a part of the surface of the electrode active material that stores and releases lithium ions. A method for producing an electrode, which comprises a step of forming a mixture containing the coated electrode active material and an organic solvent, and the amount of the organic solvent contained in the mixture is applied to the coating layer of the coated electrode active material. It is 50 to 600 parts with respect to 100 parts of the total weight of the coating resin contained, and the absolute value of the difference between the solubility parameter of the organic solvent and the solubility parameter of the coating resin is 1.5 to 4. The present invention relates to a method for manufacturing an electrode for a lithium ion battery.

According to the method for manufacturing an electrode for a lithium ion battery of the present invention, the electrode can be manufactured so that the shape of the electrode can be maintained without using the adhesive material remaining on the electrode and the energy density of the electrode is not lowered. Can be done.
Further, since the shape of the electrode is stable, it is possible to prevent the shape of the electrode from collapsing during charging and discharging, and it is possible to manufacture an electrode having excellent cycle characteristics.

FIG. 1 is a photograph of the molded articles produced in Examples 1 to 3 and Comparative Example 1 after the shape evaluation test (1 month after immersion in the electrolytic solution).

Hereinafter, the present invention will be described in detail.
The method for producing an electrode for a lithium ion battery of the present invention comprises an electrode active material containing a coated electrode active material having a coating layer containing a coating resin on at least a part of the surface of the electrode active material that stores and releases lithium ions. A method for manufacturing an electrode for a lithium ion battery having a layer, which comprises a step of forming a mixture containing the coated electrode active material and an organic solvent, and the amount of the organic solvent contained in the mixture is the coating. The total weight of the coating resin contained in the coating layer of the electrode active material is 50 to 600 parts with respect to 100 parts, and the absolute value of the difference between the solubility parameter of the organic solvent and the solubility parameter of the coating resin is 1. It is characterized by being .5-4.

First, the components of the electrode for a lithium ion battery, which is the object manufactured by the present invention, will be described.
The electrode for a lithium ion battery has an electrode active material layer containing a coated electrode active material.
The coated electrode active material is an electrode active material having a coating layer on a part of the surface of the electrode active material. The coating layer contains a coating resin.
When the surface of the electrode active material is coated with a coating layer, it becomes easy to keep the distance between the electrode active materials constant, and it becomes easy to maintain the conductive path, which is preferable.
The electrode active material layer preferably has a thickness of 150 μm or more. The method for producing an electrode for a lithium ion battery of the present invention is suitable for forming an electrode active material layer having a thickness of 150 μm or more.

The electrode active material may be a positive electrode active material or a negative electrode active material. When the electrode active material is a positive electrode active material, the electrode for a lithium ion battery becomes a positive electrode, and when the electrode active material is a negative electrode active material, the electrode for a lithium ion battery becomes a negative electrode.

Examples of the positive electrode active material as the electrode active material include a composite oxide of lithium and a transition metal {composite oxide having one type of transition metal element (LiCoO ₂ , LiNiO ₂ , LiAlMnO ₄ , LiMnO ₂ and LiMn ₂ O _{4 and the} like). ), composite oxide transition metal element is two (e.g. _{LiFeMnO 4, LiNi 1-x Co} x O 2, LiMn 1-y Co y O 2, LiNi 1/3 Co 1/3 Al 1/3 O 2 different and _{LiNi 0.8 Co 0.15 Al 0.05 O 2} ) and a composite oxide transition metal element is three or more [e.g. LiMaM'bM''cO ₂ (M, M 'and M''are each It is a transition metal element and satisfies a + b + c = 1. For example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), etc.}, lithium-containing transition metal phosphate (for example, LiFePO ₄ , LiCoPO ₄ , LiMnPO _4). And LiNiPO ₄ ), transition metal oxides (eg MnO ₂ and V ₂ O ₅ ), transition metal sulfides (eg MoS ₂ and TiS ₂ ) and conductive polymers (eg polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p). -Phenylene and polyvinylcarbazole) and the like, and two or more kinds may be used in combination.
The lithium-containing transition metal phosphate may be one in which a part of the transition metal site is replaced with another transition metal.

As the negative electrode active material, the negative electrode active material includes carbon-based materials [for example, graphite, non-graphitizable carbon, amorphous carbon, fired resin (for example, phenol resin, furan resin, etc. fired and carbonized), coke, etc. (For example, pitch coke, needle coke, petroleum coke, etc.), silicon carbide and carbon fiber, etc.], conductive polymers (for example, polyacetylene and polypyrrole, etc.), metals (tin, silicon, aluminum, zirconium, titanium, etc.), metal oxides (Titanium oxides, lithium-titanium oxides, silicon oxides, etc.) and metal alloys (for example, lithium-tin alloys, lithium-silicon alloys, lithium-aluminum alloys, lithium-aluminum-manganese alloys, etc.) and carbon-based products. Examples include a mixture with a material.
Among the above-mentioned negative electrode active materials, those which do not contain lithium or lithium ions inside may be pre-doped with a part or all of the active materials containing lithium or lithium ions in advance.

The coating layer contains a coating resin. If necessary, a conductive auxiliary agent described later may be further contained.
The coated electrode active material is one in which a part or all of the surface of the electrode active material is coated with a coating layer containing a coating resin, and the coating resin forms an electrode active material layer. Unlike the binder (also called the electrode binder) that is added to fix the active material to the electrode slurry, which is the material for this purpose, it has already adhered to the surface of the electrode active material before forming the electrode active material layer. There is.

As the coating resin constituting the coating layer, a thermoplastic resin, a thermosetting resin, or the like can be used, and preferable ones are a vinyl resin, a urethane resin, a silicone resin, and a butadiene resin [styrene butadiene copolymer resin, Butadiene polymer {butadiene rubber, liquid polybutadiene, etc.}] can be mentioned. These resins are preferable because they can follow the volume change of the active material due to charging and discharging in the electrode.
As the coating resin, a vinyl resin is particularly preferable. As the coating resin, a coating resin having a liquid absorption rate of 10% or more when immersed in an electrolytic solution and a tensile elongation at break in a saturated liquid absorption state of 10% or more is more preferable.
In the present invention, the vinyl resin is a radical polymer of a monomer having an unsaturated double bond (also referred to as a monomer), and the monomer having an unsaturated double bond is an unsaturated hydrocarbon compound (also referred to as a monomer). The hydrogen atom may be substituted with a halogen atom), and includes an ester of a carboxylic acid having an unsaturated double bond and an ester of a carboxylic acid having an unsaturated double bond.

The liquid absorption rate when immersed in the electrolytic solution is calculated by the following formula by measuring the weight of the coating resin before and after immersion in the electrolytic solution.
Liquid absorption rate (%) = [(Weight of coating resin after immersion in electrolytic solution-Weight of coating resin before immersion in electrolytic solution) / Weight of coating resin before immersion in electrolytic solution] × 100
The electrolytic solution for determining the liquid absorption rate is preferably a mixed solvent in which ethylene carbonate (EC) and propylene carbonate (PC) are mixed in a volume ratio of EC: PC = 1: 1 and LiPF ₆ as an electrolyte is 1 mol / mol /. An electrolytic solution dissolved so as to have a concentration of L is used.
Immersion in the electrolytic solution for determining the liquid absorption rate is performed at 50 ° C. for 3 days. By immersing at 50 ° C. for 3 days, the coating resin is in a saturated liquid absorbing state. The saturated liquid absorbing state means a state in which the weight of the coating resin does not increase even if it is further immersed in the electrolytic solution.
The electrolytic solution used when manufacturing the lithium ion battery using the electrode for the lithium ion battery of the present invention is not limited to the above electrolytic solution, and other electrolytic solutions may be used.

When the liquid absorption rate is 10% or more, lithium ions can easily permeate the coating resin, so that the ion resistance in the electrode active material layer can be kept low. If the liquid absorption rate is less than 10%, the conductivity of lithium ions becomes low, and the performance as a lithium ion battery may not be sufficiently exhibited.
The liquid absorption rate is preferably 20% or more, and more preferably 30% or more.
The preferable upper limit value of the liquid absorption rate is 400%, and the more preferable upper limit value is 300%.

For the tensile elongation at break in the saturated liquid absorption state, the coating resin is punched out in a dumbbell shape and immersed in the electrolytic solution at 50 ° C. for 3 days in the same manner as the above measurement of the liquid absorption rate to saturate the coating resin. As a state, it can be measured according to ASTM D683 (test piece shape Type II). The tensile elongation at break is a value calculated by the following formula as the elongation at break until the test piece breaks in the tensile test.
Tensile breaking elongation (%) = [(Test piece length at break-Test piece length before test) / Test piece length before test] x 100

When the tensile elongation at break of the coating resin in the saturated liquid absorbing state is 10% or more, the coating resin has appropriate flexibility, and therefore, the coating resin is included due to the volume change of the electrode active material during charging and discharging. It becomes easy to suppress the peeling of the coating layer.
The tensile elongation at break is preferably 20% or more, and more preferably 30% or more.
Further, the preferable upper limit value of the tensile elongation at break is 400%, and the more preferable upper limit value is 300%.

Among the vinyl resins, the group consists of a monomer (a1) having a carboxyl group or an acid anhydride group and an unsaturated double bond, a monomer (a2) represented by the following general formula (1), vinylidene fluoride and acrylonitrile. It is preferably a polymer (A1) of a monomer composition containing at least one selected.
CH ₂ = C (R ¹ ) COOR ² (1)
[In the formula (1), R ¹ is a hydrogen atom or a methyl group, and R ² is a straight chain having 4 to 12 carbon atoms or a branched alkyl group having 3 to 36 carbon atoms. ]

Examples of the monomer (a1) having a carboxyl group or an acid anhydride group and an unsaturated double bond include monocarboxylic acids having 3 to 15 carbon atoms such as (meth) acrylic acid (a11), crotonic acid, and itaconic acid; Dicarboxylic acids having 4 to 24 carbon atoms such as (anhydrous) maleic acid, fumaric acid, (anhydrous) itaconic acid, citraconic acid, and mesaconic acid; trivalent to tetravalent or higher valences of 6 to 24 carbon atoms such as aconitic acid. A number of polycarboxylic acids and the like can be mentioned. Among these, (meth) acrylic acid (a11) is preferable, and methacrylic acid is more preferable.

In the monomer (a2) represented by the general formula (1), R ¹ represents a hydrogen atom or a methyl group. R ¹ is preferably a methyl group.
R ² is a linear or branched alkyl group having 4 to 12 carbon atoms, or is preferably a branched alkyl group having 13 to 36 carbon atoms.

(A21) ^{Ester compound in which R 2} 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 and an octyl group. Examples thereof include a nonyl group, a decyl group, an undecyl group and a dodecyl group.
The branched alkyl group having 4 to 12 carbon atoms includes a 1-methylpropyl group (sec-butyl group), a 2-methylpropyl group, a 1,1-dimethylethyl group (tert-butyl group), a 1-methylbutyl group, and 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-Mech Rudecyl 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-methylundesyl group, 3-methylundesyl group, 4-methylundesyl group, 5-methylundesyl group, 6-methylundesyl group, 7 -Methylundecyl group, 8-methylundesyl group, 9-methylundesyl group, 10-methylundesyl 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. Of these, a 2-ethylhexyl group is particularly preferable.

( ^{A22) Estel compound in which R 2} is a branched alkyl group having 13 to 36 carbon atoms As the branched alkyl group having 13 to 36 carbon atoms, a 1-alkylalkyl group [1-methyldodecyl group, 1-butyleicosyl group, 1-hexyl octadecyl group, 1-octyl hexadecyl group, 1-decyl tetradecyl group, 1-undecyl tridecyl group, etc.], 2-alkylalkyl group [2-methyldodecyl group, 2-hexyl octadecyl group, 2- Octyl hexadecyl group, 2-decyl tetradecyl group, 2-undecyl tridecyl group, 2-dodecyl hexadecyl group, 2-tridecyl pentadecyl group, 2-decyl octadecyl group, 2-tetradecyl octadecyl group, 2- Hexadecyl octadecyl group, 2-tetradecyl eikosyl group, 2-hexadecyl eikosyl group, etc.] 3-34-alkylalkyl groups (3-alkylalkyl groups, 4-alkylalkyl groups, 5-alkylalkyl groups, 32 -Alkylalkyl group, 33-alkylalkyl group, 34-alkylalkyl group, etc.), propylene oligomer (7 to 11 mer), ethylene / propylene (molar ratio 16/1 to 1/11) oligomer, isobutylene oligomer ( One or more branched alkyl groups such as residues obtained by removing hydroxyl groups from oxoalcohols obtained from 7 to 8 mer) and α-olefin (5 to 20 carbon atoms) oligomers (4 to 8 mer), etc. Examples thereof include mixed alkyl groups contained therein.

The polymer (A1) preferably further contains an ester compound (a3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid.
Examples of the monohydric aliphatic alcohol having 1 to 3 carbon atoms constituting the ester compound (a3) include methanol, ethanol, 1-propanol and 2-propanol.

The content of the ester compound (a3) is preferably 10 to 60% by weight, preferably 15 to 55% by weight, based on the total weight of the polymer (A1) from the viewpoint of suppressing volume change of the electrode active material. Is more preferable, and 20 to 50% by weight is further preferable.

Further, the polymer (A1) may further contain a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group.
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.
Anionic monomers having a polymerizable unsaturated double bond and an anionic group are compounds obtained by combining these, and examples thereof include vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid and (meth) acrylic acid. Be done.
The (meth) acryloyl group means an acryloyl group and / or a methacryloyl group.
Examples of the cation constituting the salt (a4) of the anionic monomer include lithium ion, sodium ion, potassium ion, ammonium ion and the like.

When the salt (a4) of the anionic monomer is contained, the content thereof is preferably 0.1 to 15% by weight based on the total weight of the coating resin from the viewpoint of internal resistance and the like. It is more preferably ~ 15% by weight, and even more preferably 2-10% by weight.

As the polymer (A1), a polymer (A11) containing (meth) acrylic acid (a11) and an ester compound (a21), polyvinylidene fluoride and polyacrylonitrile are preferable.
The polymer (A11) more preferably further contains an ester compound (a3), particularly preferably methacrylic acid as the (meth) acrylic acid (a11) and 2-ethylhexyl methacrylate as the ester compound (a21). It is a copolymer of methacrylic acid, 2-ethylhexyl methacrylate and methyl methacrylate using methyl methacrylate as the ester compound (a3).

When the coating resin is a polymer (A11), the polymer (A11) includes (meth) acrylic acid (a11), the above-mentioned monomer (a2), a monovalent aliphatic alcohol having 1 to 3 carbon atoms, and (meth). ) A monomer composition containing an ester compound (a3) with acrylic acid and a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group used as necessary is polymerized. Therefore, the weight ratio of the monomer (a2) to the (meth) acrylic acid (a11) [the ester compound (a21) / the (meth) acrylic acid (a11)] is 10/90 to 90/10. Is preferable.
When the weight ratio of the monomer (a2) to the (meth) acrylic acid (a11) is 10/90 to 90/10, the polymer obtained by polymerizing the monomer (a2) has good adhesion to the electrode active material and is peeled off. It becomes difficult.
The weight ratio is preferably 30/70 to 85/15, more preferably 40/60 to 70/30.

Further, the monomer constituting the polymer (A1) includes a monomer (a1) having a carboxyl group or an acid anhydride group and an unsaturated double bond as long as the physical properties of the polymer (A1) are not impaired. A radically polymerizable monomer (a5) copolymerizable with the monomer (a2) represented by the general formula (1), vinylidene fluoride and acrylonitrile may be contained.
As the radically polymerizable monomer (a5), a monomer containing no active hydrogen is preferable, and the following monomers (a51) to (a58) can be used.

(A51) Hydro formed from a linear aliphatic monool having 13 to 20 carbon atoms, an alicyclic monool having 5 to 20 carbon atoms, or an aromatic aliphatic monool having 7 to 20 carbon atoms and (meth) acrylic acid. Calvir (meth) acrylate Examples of the monool include (i) linear aliphatic monool (tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecil alcohol, and araxyl alcohol. Etc.), (iii) alicyclic monool (cyclopentyl alcohol, cyclohexyl alcohol, cycloheptyl alcohol, cyclooctyl alcohol, etc.), (iii) aromatic aliphatic monool (benzyl alcohol, etc.) and a mixture of two or more thereof. Can be mentioned.

(A52) Poly (n = 2 to 30) Oxyalkylene (2 to 4 carbon atoms) Alkyl (1 to 18 carbon atoms) Ether (meth) Acrylate [Methanol ethylene oxide (hereinafter abbreviated as EO) 10 mol adduct (meth) ) Acrylate, methanol propylene oxide (hereinafter abbreviated as PO) 10 mol adduct (meth) acrylate, etc.]

(A53) Nitrogen-containing vinyl compound (a53-1) Amide group-containing vinyl compound (i) (Meta) acrylamide compound having 3 to 30 carbon atoms, such as N, N-dialkyl (1 to 6 carbon atoms) or dialalkyl (carbon number) 7 to 15) (meth) acrylamide (N, N-dimethylacrylamide, N, N-dibenzylacrylamide, etc.), diacetoneacrylamide (ii) Excluding the above (meth) acrylamide compound, containing an amide group having 4 to 20 carbon atoms Vinyl compounds such as N-methyl-N-vinylacetamide, cyclic amides [pyrrolidone compounds (6 to 13 carbon atoms, for example, N-vinylpyrrolidone)]

(A53-2) (Meta) Acrylate Compound (i) Dialkyl (1 to 4 Carbons) Aminoalkyl (1 to 4 Carbons) (Meta) Acrylate [N, N-Dimethylaminoethyl (Meta) Acrylate, N, N -Diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, morpholinoethyl (meth) acrylate, etc.]
(Ii) Quaternary ammonium group-containing (meth) acrylate {tertiary amino group-containing (meth) acrylate [N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, etc.] Compounds (quaternized with a quaternary agent such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate), etc.}

(A53-3) Heterocyclic-containing vinyl compound pyridine compound (7 to 14 carbon atoms, for example 2- or 4-vinylpyridine), imidazole compound (5 to 12 carbon atoms, for example N-vinylimidazole), pyrrole compound (carbon number) 6 to 13, for example N-vinylpyrrole), pyrrolidone compounds (6 to 13 carbon atoms, for example N-vinyl-2-pyrrolidone)

(A54) Vinyl Hydrocarbons (a54-1) Aliphatic Vinyl Hydrocarbons Olefins with 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.

(A54-2) Alicyclic vinyl hydrocarbons Cyclic unsaturated compounds having 4 to 18 or more carbon atoms, such as cycloalkene (eg, cyclohexene), (di) cycloalkene [eg, (di) cyclopentadiene], terpenes ( For example, pinene and limonene), inden

(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, and butyl. Styrene, phenylstyrene, cyclohexylstyrene, benzylstyrene

(A55) Vinyl Ester Aliphatic Vinyl Ester [Alkenyl ester of an aliphatic carboxylic acid (mono- or dicarboxylic acid) having 4 to 15 carbon atoms (for example, vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, etc. Vinyl methoxyacetate)]
Aromatic vinyl ester [containing 9 to 20 carbon atoms, for example, an alkenyl ester of an aromatic carboxylic acid (mono- or dicarboxylic acid) (for example, vinylbenzoate, diallylphthalate, methyl-4-vinylbenzoate), and an aromatic ring of an aliphatic carboxylic acid. Ester (eg acetoxystyrene)]

(A56) Vinyl Ether Aliphatic Vinyl Ether [3 to 15 carbon atoms, for example, vinyl alkyl (1 to 10 carbon atoms) ether (vinyl methyl ether, vinyl butyl ether, vinyl 2-ethylhexyl ether, etc.), vinyl alkoxy (1 to 6 carbon atoms) Alkyl (1 to 4 carbon atoms) ether (vinyl-2-methoxyethyl ether, methoxybutadiene, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxydiethyl ether, vinyl-2-ethyl Mercaptoethyl ether, etc.), Poly (2-4) (meth) allyloxyalkane (2 to 6 carbon atoms) (dialyloxyetane, trialiloxietan, tetraaryloxybutane, tetramethalyloxyetane, etc.)], Aromatic vinyl ether (8 to 20 carbon atoms, for example vinyl phenyl ether, phenoxystyrene)

(A57) Vinyl Ketone Aliphatic Vinyl Ketone (4 to 25 Carbons, For example, Vinyl Methyl Ketone, Vinyl Ethyl Ketone), Aromatic Vinyl Ketone (9 to 21, For example, Vinyl Phenyl Ketone)

(A58) Unsaturated Dicarboxylic Acid Diester An unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms, for example, a dialkyl fumarate (two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms). ), Dialkylmaleate (two alkyl groups are linear, branched or alicyclic groups with 1-22 carbon atoms)

Among those exemplified as (a5) above, (a51), (a52) and (a53) are preferable from the viewpoint of withstand voltage.

In the polymer (A11), a monomer (a1) having a carboxyl group or an acid anhydride group and an unsaturated double bond, a monomer (a2) represented by the above general formula (1), and 1 of 1 to 3 carbon atoms. An ester compound (a3) of a valent aliphatic alcohol and (meth) acrylic acid, a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group, and a radically polymerizable monomer (a5). ) Is 0.1 to 80% by weight in (a1), 0.1 to 99.9% by weight in (a2), and 0 to 60 in (a3), based on the weight of the polymer (A1). By weight%, (a4) is preferably 0 to 15% by weight, and (a5) is preferably 0 to 99.8% by weight.
When the content of the monomer is within the above range, the liquid absorbency into the non-aqueous electrolytic solution becomes good.

The preferred lower limit of the number average molecular weight of the polymer (A11) is 3,000, more preferably 50,000, still more preferably 60,000, and the preferred upper limit is 2,000,000, more preferably 1,500,000. , More preferably 1,000,000, particularly preferably 120,000.

The number average molecular weight of the polymer (A11) can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.
Equipment: Alliance GPC V2000 (manufactured by Waters)
Solvent: Ortodichlorobenzene Standard substance: Polystyrene detector: RI
Sample concentration: 3 mg / ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 in series (manufactured by Polymer Laboratories)
Column temperature: 135 ° C

The polymer (A11) is a known polymerization initiator {azo-based initiator [2,2'-azobis (2-methylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile, etc.)]. , Peroxide-based initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.)} by known polymerization methods (mass polymerization, solution polymerization, emulsification polymerization, suspension polymerization, etc.) Can be manufactured.
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 monomers from the viewpoint of adjusting the number average molecular weight to a preferable range. More preferably, it is 0.1 to 1.5% by weight, and the polymerization temperature and the polymerization time are adjusted according to the type of the polymerization initiator and the like, but the polymerization temperature is usually −5 to 150 ° C. (preferably 30 to 30 to 30 to 100% by weight). 120 ° C.), the reaction time is usually 0.1 to 50 hours (preferably 2 to 24 hours).

Solvents used in the case of solution polymerization include, for example, esters (2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (1 to 8 carbon atoms, such as methanol, ethanol and octanol), and hydrocarbons (carbon atoms). Examples thereof include 4 to 8, for example, n-butane, cyclohexane and toluene) and ketones (3 to 9 carbon atoms, for example, methyl ethyl ketone), and the amount used is the total amount of monomers from the viewpoint of adjusting the number average molecular weight to a preferable range. Based on the weight, it is usually 5 to 900% by weight, preferably 10 to 400% by weight, more preferably 30 to 300% by weight, and the monomer concentration is usually 10 to 95% by weight, preferably 20 to 90% by weight. More preferably, it is 30 to 80% by weight.

Examples of the dispersion medium in emulsification polymerization and suspension polymerization include water, alcohol (for example, ethanol), ester (for example, ethyl propionate), and light naphtha, and examples of emulsifier include higher fatty acid (10 to 24 carbon atoms) metal salt. (For example, sodium oleate and sodium stearate), higher alcohol (10 to 24 carbon atoms) sulfate ester metal salt (for example, sodium lauryl sulfate), tetramethyldecinediol ethoxylated, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. Can be mentioned. Further, polyvinyl alcohol, polyvinylpyrrolidone and the like may be added as stabilizers.
The monomer concentration of the solution or dispersion is usually 5 to 95% by weight, preferably 10 to 90% by weight, more preferably 15 to 85% by weight, and the amount of the polymerization initiator used is usually based on the total weight of the monomers. It is 0.01 to 5% by weight, preferably 0.05 to 2% by weight.
For 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. ..

Crosslinking agent (A') having a reactive functional group that reacts the polymer (A11) with a carboxyl group {preferably polyepoxy compound (a'1) [polyglycidyl ether (bisphenol A diglycidyl ether, propylene glycol diglycidyl ether) And glycerin triglycidyl ether, etc.) and polyglycidylamine (N, N-diglycidylaniline and 1,3-bis (N, N-diglycidylaminomethyl)), etc.] and / or polyol compound (a'2) (ethylene) A crosslinked polymer obtained by cross-linking with (glycol or the like)} may be used as a coating resin.

Examples of the method of cross-linking the polymer (A11) using the cross-linking agent (A') include a method of coating the electrode active material with the polymer (A1) and then cross-linking. Specifically, by mixing the electrode active material and a resin solution containing the polymer (A1) and removing the solvent, a coated electrode active material in which the electrode active material is coated with the polymer (A1) is produced, and then cross-linked. A solution containing the agent (A') is mixed with the coated electrode active material and heated to cause a solvent removal and a cross-linking reaction, and the polymer (A1) is cross-linked and coated by the cross-linking agent (A'). Examples thereof include a method in which a reaction that becomes a polymer is caused on the surface of the electrode active material.
The heating temperature is adjusted according to the type of the cross-linking agent, but is usually 70 ° C. or higher when the polyepoxy compound (a'1) is used as the cross-linking agent, and is usually 70 ° C. or higher when the polyol compound (a'2) is used. It is 120 ° C. or higher.

The polyvinylidene fluoride and polyacrylonitrile are obtained by polymerizing a monomer by a known method, but commercially available polyvinylidene fluoride and polyacrylonitrile may be used.

The coating layer may further contain a conductive auxiliary agent. Above all, when the electrode active material is a positive electrode active material, it is preferable to contain a conductive auxiliary agent.
The conductive auxiliary agent is selected from materials having conductivity, and specifically, carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), etc.], PAN-based carbon. Carbon fibers such as fibers and pitch-based carbon fibers, carbon nanofibers, carbon nanotubes, and metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.] can be used.
These conductive auxiliaries may be used alone or in combination of two or more. Moreover, you may use these alloys or metal oxides. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and mixtures thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is even more preferable. Further, as these conductive auxiliaries, a conductive material (a metal one among the above-mentioned conductive materials) may be coated around a particle-based ceramic material or a resin material by plating or the like. Polypropylene resin kneaded with graphene is also preferable as a conductive auxiliary agent.

The average particle size of the conductive auxiliary agent is not particularly limited, but is preferably 0.01 to 10 μm, preferably 0.02 to 5 μm, from the viewpoint of the electrical characteristics of the electrode for the lithium ion battery. More preferably, it is 0.03 to 1 μm. In the present specification, the particle size of the conductive auxiliary agent means the maximum distance L among the distances between arbitrary two points on the contour line of the particles formed by the conductive auxiliary agent. As the value of the "average particle size of the conductive auxiliary agent", the particle size of the particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of is adopted.

The shape (form) of the conductive auxiliary agent is not limited to the particle form, and may be a form other than the particle form, and may be, for example, a fibrous conductive auxiliary agent.
As the fibrous conductive auxiliary agent, the surface of a conductive fiber formed by uniformly dispersing a metal having good conductivity or graphite in a synthetic fiber, a metal fiber made of a metal such as stainless steel, or an organic fiber can be used. Examples thereof include conductive fibers coated with a metal, conductive fibers in which the surface of an organic substance is coated with a resin containing a conductive substance, and the like.
The average fiber diameter of the fibrous conductive auxiliary agent is preferably 0.1 to 20 μm.

When the coating layer contains a conductive auxiliary agent, the weight of the conductive auxiliary agent contained in the coating layer is preferably 15 to 75% by weight based on the total weight of the coating resin and the conductive auxiliary agent.
When the coating layer of the coated electrode active material contains a conductive auxiliary agent, even if the SEI film is formed on the surface of the electrode active material after precharging, it is activated by the effect of the conductive auxiliary agent contained in the coating layer. It is preferable because the conduction path between the substances can be maintained and the increase in resistance due to the formation of the SEI film can be suppressed, and it is more preferable that the ratio of the conductive auxiliary agent is in this range because the resistance can be easily suppressed.

For the coated electrode active material, for example, in a state where the electrode active material is placed in a universal mixer and stirred at 30 to 50 rpm, a coating resin solution containing a coating resin is added dropwise over 1 to 90 minutes, and further required. It can be obtained by mixing the conductive auxiliary agent accordingly, raising the temperature to 50 to 200 ° C. with stirring, reducing the pressure to 0.007 to 0.04 MPa, and then holding the mixture for 10 to 150 minutes.
The weight ratio of the electrode active material to the coating resin in the coated electrode active material is preferably electrode active material / coating resin = 90 / 10-99.99 / 0.01.

The method for producing an electrode for a lithium ion battery of the present invention includes a step of molding a mixture containing a coated electrode active material and an organic solvent, and comprises a solubility parameter of the organic solvent (hereinafter abbreviated as SP value) and a coating resin. The absolute value of the difference in the solubility parameter of is 1.5 to 4. If the absolute value of the difference between the SP value of the organic solvent and the SP value of the coating resin exceeds 4, the adhesive strength of the surface of the coated electrode active material is not sufficiently developed and the shape of the battery cannot be maintained. If the absolute value of the difference between the SP value of the organic solvent and the SP value of the coating resin is less than 1.5, the coating layer on the surface of the coated electrode active material will dissolve and disappear, so the shape of the battery should be maintained. I can't.

In the present invention, the SP value is calculated by the Fedors method. The SP value can be expressed by the following equation.
SP value (δ) = (ΔH / V) ^1/2
However, in the formula, ΔH represents the molar heat of vaporization (cal), and V represents the molar volume (cm ³ ).
Further, ΔH and V are the sum of the molar heats of vaporization (ΔH) of the atomic groups described in “POLYMER ENGINEERING AND SCIENCE, 1974, Vol. 14, No. 2, ROBERT F. FEDORS. The total molar volume (V) can be used.
Those with similar values are easy to mix with each other (high compatibility), and those with different values are difficult to mix.
The fact that the absolute value of the difference in the solubility parameter is in this range means that the organic solvent and the coating resin are easily mixed, and the coating resin easily absorbs the organic solvent and swells. That is, when a mixture is formed, a part of the coating resin contained in the coating layer is dissolved in an organic solvent, and adhesiveness is developed on the surface of the coating layer to obtain a mixture having physical properties suitable for molding.

The organic solvent used in the production method of the present invention is not limited as long as the absolute value of the difference between the SP value of the organic solvent and the SP value of the coating resin contained in the coating layer is 1.5 to 4, and the coating layer can be used. It can be selected according to the type of coating resin contained. Among them, an aprotic solvent can be preferably used from the viewpoint that it can be used for many coating resins.
The aprotic solvent is a solvent that does not have a hydrogen ion donating group (a group having a dissociative hydrogen atom, for example, an amino group, a hydroxyl group, and a thio group).
Examples of the solvent that can be preferably used as the organic solvent include nitrile compounds, amide compounds, sulfones and the like, and mixtures thereof.

Examples of the nitrile compound include acetonitrile, and examples of the amide compound include N, N-dimethylformamide (hereinafter, also referred to as DMF).
Examples of the sulfone include a chain sulfone such as dimethyl sulfone and diethyl sulfone, a cyclic sulfone such as sulfolane, and the like.
Of these, N, N-dimethylformamide (DMF) is preferred.

As the organic solvent in the present invention, a solvent other than the above-mentioned aprotic solvent can be used, and an aliphatic alcohol having 1 to 4 carbon atoms (ethanol or the like) can also be preferably used from the viewpoint of molding time and the like.

Further, as a preferable combination of the coating resin and the organic solvent contained in the coating layer of the coating electrode active material, a combination in which the coating resin is a vinyl resin and the organic solvent is N, N-dimethylformamide can be mentioned for coating. The resin is a polymer of a monomer composition containing a monomer (a1) having a carboxyl group or an acid anhydride group and an unsaturated double bond and a monomer (a2) represented by the general formula (1). A combination in which the organic solvent is N, N-dimethylformamide is more preferable.

The mixture preferably does not contain a binder. In the present invention, the binder is an electrode binder used for adhering active materials to each other and between the active material and the current collector in a lithium ion battery, and is a material for forming an electrode active material layer (the electrode active material and the electrode active material). It means a known material that is added and used as a binder to an electrode slurry which is a mixture containing a solvent.
Examples of such a binder include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene and polypropylene. The binder is contained as a binder solution dissolved in a solvent in the electrode slurry for forming the electrode active material layer, whereas the coating resin is also contained in the electrode slurry. It differs in that it is contained in the coating layer on the surface.

The mixture may contain a conductive material in addition to the above-mentioned conductive auxiliary agent contained in the coating layer. It is preferable to include a conductive material because it is easy to maintain a conductive path between active materials.
As the conductive material, the same conductive material as the above-mentioned conductive auxiliary agent contained in the coating layer can be used, and the preferred one is also the same.

The blending ratio of each component contained in the mixture is such that the amount of the organic solvent is 50 to 600 parts with respect to 100 parts of the total weight of the coating resin contained in the coating layer of the coating electrode active material. If the amount of the organic solvent is less than 50 parts with respect to the total weight of 100 parts of the coating resin, the adhesive force on the surface of the coated electrode active material is not sufficiently developed and the shape of the battery cannot be maintained, and 600 parts are used. If it exceeds the limit, the coating layer on the surface of the coated electrode active material will dissolve, and the shape of the battery cannot be maintained.
Further, the blending ratio of the coated electrode active material and the organic solvent in the mixture is not limited as long as the blending ratio of the coating resin and the organic solvent contained in the coating layer of the coated electrode active material is a predetermined ratio. However, from the viewpoint of uniformity and the like, it is preferable that the coated electrode active material is 90 to 99% by weight and the organic solvent is 1 to 10% by weight based on the total weight of the coated electrode active material and the organic solvent.
When a conductive material is further contained, it is preferable that the conductive material is contained in an amount of 0 to 5% by weight.

In the method for producing an electrode for a lithium ion battery of the present invention, the above mixture is molded.
Any method may be used for molding as long as a mixture containing the coated electrode active material and the organic solvent can be molded.
For example, a method of filling a mixture in a mold and compression molding, and a method of molding by extrusion molding can be mentioned.

The compression molding can be performed by using an arbitrary pressurizing device such as a hydraulic press device and a pressurizing jig. For example, a mixture is placed in a cylindrical bottomed container, a round bar-shaped pressurizing jig having a diameter slightly smaller than the inner diameter of the cylinder is inserted from above, and the mixture is compressed by a pressurizing device to form a cylindrical shape. A molded body molded into the above is obtained.
By changing the shape of the pressurizing jig, a molded product having an arbitrary shape can be obtained.

As the compression condition in the compression molding, the pressure applied to the mixture is preferably 100 to 3000 MPa. The pressurization time is preferably 1 to 300 seconds.

The compression molding may be performed on the current collector. By arranging the mixture on the current collector and performing compression molding, an electrode active material layer can be obtained on the current collector.
The electrode active material layer obtained on the current collector can be used together with the current collector as an electrode for a lithium ion battery.

Examples of the material constituting the positive electrode current collector as the current collector include copper, aluminum, titanium, stainless steel, nickel, calcined carbon, a conductive polymer, and conductive glass. Further, as the positive electrode current collector, a resin current collector composed of a conductive agent and a resin may be used.

Examples of the material constituting the negative electrode current collector as the current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel and alloys thereof. Of these, copper is preferable from the viewpoint of weight reduction, corrosion resistance, and high conductivity. The negative electrode current collector may be a current collector made of fired carbon, a conductive polymer, conductive glass, or the like, or a resin current collector made of a conductive agent and a resin.

As the conductive agent constituting the resin current collector, the same as the conductive material which is an arbitrary component of the mixture can be preferably used for both the positive electrode current collector and the negative electrode current collector.
Examples of the resin constituting the resin current collector include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), and polytetra. Fluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylic nitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin, or a mixture thereof, etc. Can be mentioned.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferable, and polyethylene (PE), polypropylene (PP) and polymethylpentene are more preferable. (PMP).

By the above steps, an electrode for a lithium ion battery having an electrode active material layer can be manufactured.
The electrode active material layer obtained by the above step is contained in the coating layer of the coated electrode active material even though the binder for adhering the active materials to each other and the active material and the current collector is not used. The shape of the electrode active material layer can be maintained by the coating resin.

When manufacturing a lithium ion battery, the electrode for a lithium ion battery manufactured by the method for manufacturing an electrode for a lithium ion battery of the present invention is housed in a cell container together with a separator, and an electrolytic solution is injected into the electrode active material layer. It is preferable to impregnate the electrolytic solution.
As the electrode active material layer to be housed in the cell container, both the positive electrode for the lithium ion battery and the negative electrode for the lithium ion battery manufactured by the method for manufacturing the electrode for the lithium ion battery of the present invention may be used, or only one of them may be used. You may.
When only one is used, a known counter electrode can be used as the opposite electrode.

Since the obtained molded product maintains a constant shape, it is easy to handle, and the molded product can be easily stored in the cell container.
Further, as described above, when the electrode active material layer is obtained on the current collector, it is also possible to manufacture a lithium ion battery by using the electrode active material layer as an electrode together with the current collector. ..

As the separator, a porous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and a porous polypropylene, a non-woven fabric made of synthetic fibers (polyester fiber, aramid fiber, etc.) or glass fiber, and silica on the surface thereof. , Known separators for lithium-ion batteries, such as those to which ceramic fine particles such as alumina and titania are attached.

As the electrolytic solution, an electrolytic solution containing an electrolyte and a non-aqueous solvent, which is used in the production of a known lithium ion battery, can be used.

As the electrolyte, those used in ordinary electrolytes can be used, and preferred ones are lithium salt-based electrolytes of inorganic acids such as _{LiPF 6} , LiBF ₄ , LiSbF ₆ , _{LiAsF 6} and LiClO _4. A sulfonylimide-based electrolyte having fluorine atoms such as LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) _{2 , and fluorine atoms such as LiC (CF 3} SO ₂ ) ₃ Examples thereof include sulfonylmethide electrolytes having.

As the non-aqueous solvent used for the electrolytic solution, a lactone compound, a cyclic carbonate ester, a chain carbonate ester and a mixed solvent thereof are preferable from the viewpoint of the output of the lithium ion battery and charge / discharge cycle characteristics, and the cyclic carbonate and cyclic. A mixed solvent of carbonic acid ester and chain carbonate is more preferable, and most preferable is propylene carbonate (PC), a mixed solution of ethylene carbonate (EC) and propylene carbonate (PC), ethylene carbonate (EC) and dimethyl carbonate ( A mixed solution of DMC) and a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC).

The concentration of the above-mentioned electrolyte contained in the electrolytic solution is preferably 0.3 to 3M from the viewpoint of battery characteristics at low temperature and the like.

Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples as long as the gist of the present invention is not deviated. Unless otherwise specified, parts mean parts by weight and% means% by weight.

<Production Example 1: Preparation of coating resin (A-1) and its solution>
407.9 parts of DMF was charged into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas introduction tube, and the temperature was raised to 75 ° C. Next, a monomer compounding solution containing 242.8 parts of methacrylic acid, 97.1 parts of methyl methacrylate, 242.8 parts of 2-ethylhexyl methacrylate, and 116.5 parts of DMF, and 2,2'-azobis (2,4-dimethyl). 1.7 parts of valeronitrile) and 4.7 parts of 2,2'-azobis (2-methylbutyronitrile) dissolved in 58.3 parts of DMF and an initiator solution were added to the four-necked flask while blowing nitrogen into the flask. Under stirring, radical polymerization was carried out by continuously dropping with a dropping funnel over 2 hours. After completion of the dropping, the reaction was continued at 75 ° C. for 3 hours. Then, the temperature was raised to 80 ° C. and the reaction was continued for 3 hours to obtain a copolymer solution having a resin concentration of 50%. 789.8 parts of DMF was added thereto to obtain a coating resin solution (A'-1) having a resin solid content concentration of 30% by weight.
The SP value of the coating resin contained in the coating resin solution is 10.1.

<Production Example 2: Preparation of coating resin (A-2) and its solution>
83 parts of DMF and 17 parts of methanol were placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas introduction tube, and the temperature was raised to 68 ° C. Next, 29.1 parts of methacrylic acid, 29.1 parts of butyl methacrylate, 349.7 parts of 2-ethylhexyl methacrylate, 174.8 parts of an acrylate having a branched alkyl group having 24 carbon atoms (2-decyltetradecyl methacrylate), DMF 52. Four parts of a monomer mixture containing 1 part and 10.7 parts of methanol and an initiator solution prepared by dissolving 0.263 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) in 34.2 parts of DMF. While blowing nitrogen into the mouth flask, radical polymerization was carried out by continuously dropping the mixture over 4 hours with a dropping funnel under stirring. After completion of the dropping, an initiator solution prepared by dissolving 0.583 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) in 26 parts of ethyl acetate was continuously added over 2 hours using a dropping funnel. Further, the polymerization was continued at the boiling point for 4 hours. After removing the solvent and obtaining 582 parts of the resin, 1,360 parts of isopropanol was added to obtain a coating resin solution (A'-2) containing a copolymer at a resin concentration of 30% by weight.
The SP value of the coating resin contained in the coating resin solution is 9.5.

<Production Example 3: Preparation of coating resin (A-3) and its solution>
In a four-necked flask equipped with a stirrer, thermometer, reflux condenser and nitrogen gas introduction tube, 400 parts of DMF and 100 parts of acrylonitrile, 0.2 parts of 2,2'-azobis (2,4-dimethylvaleronitrile), Add 0.4 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) and 0.1 part of octyl mercaptan, raise the temperature to 60 ° C, and blow nitrogen into a four-necked flask at 60 ° C. The polymerization was continued for 4 hours. Then, the temperature was raised to 80 ° C., and the polymerization was further continued at 80 ° C. for 6 hours. After removing the solvent and obtaining 582 parts of the resin, 1,360 parts of isopropanol was added to obtain a coating resin solution (A'-3) containing polyacrylonitrile at a resin concentration of 30% by weight.
The SP value of polyacrylonitrile is 15.4.

<Production Example 4: Preparation of electrolyte>
_{LiPF 6} was dissolved in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC) at a ratio of 1 mol / L to prepare an electrolytic solution for a lithium ion battery.

<Example 1>
100 parts of non-graphitizable carbon powder (average particle size 20 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by EarthTechnica Co., Ltd.] and stirred at room temperature at 720 rpm, and the coating obtained in Production Example 1 was obtained. 3.0 parts of the resin solution (A'-1) for use was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 6.1 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], which is a conductive auxiliary agent, was added in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 8 hours to distill off the volatile components. .. The obtained powder was classified by a sieve having a mesh size of 212 μm to obtain a coated negative electrode active material (P-1).

A mixture is prepared by mixing 100 parts of the coated negative electrode active material (P-1) and 5 parts of N, N-dimethylformamide (DMF), and the mixture is placed in a pressure jig and compression-molded to form a mixture. Then, the molded product was further allowed to stand in a vacuum dryer set at 110 ° C. to evaporate DMF to prepare a molded product as a negative electrode active material layer having a thickness of 400 μm.
The organic solvent contained in the mixture is DMF, and its SP value is 12.0.
The absolute value of the difference in SP value between the coating resin and the organic solvent (DMF) is 1.9.
Further, the amount of the organic solvent is 594 parts with respect to the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Example 2>
A coated negative electrode active material was prepared in the same manner as in Example 1 except that the amount of the coating resin solution used for producing the coated negative electrode active material was changed from 3.0 parts to 10.0 parts, and subsequently molded. The body was made.
The amount of the organic solvent is 182 parts based on the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Example 3>
A coated negative electrode active material was prepared in the same manner as in Example 1 except that the amount of the coating resin solution used for producing the coated negative electrode active material was changed from 3.0 parts to 16.7 parts, followed by molding. The body was made.
The amount of the organic solvent is 111 parts with respect to 100 parts of the total weight of the coating resin contained in the coating layer of the coating electrode active material.

<Example 4>
A coated negative electrode active material was prepared in the same manner as in Example 1 except that the amount of the coating layer resin solution used for producing the coated negative electrode active material was changed from 3.0 parts to 34.5 parts, followed by molding. The body was made.
The amount of the organic solvent is 56 parts with respect to 100 parts of the total weight of the coating resin contained in the coating layer of the coating electrode active material.

<Example 5>
100 parts of non-graphitizable carbon powder (average particle size 20 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by EarthTechnica Co., Ltd.] and stirred at room temperature at 720 rpm, and the coating obtained in Production Example 2 was obtained. 3.0 parts of the resin solution (A'-2) for use was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 6.1 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], which is a conductive auxiliary agent, was added in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 8 hours to distill off the volatile components. .. The obtained powder was classified by a sieve having a mesh size of 212 μm to obtain a coated negative electrode active material (P-5).

100 parts of this coated negative electrode active material (P-5) and 5 parts of N, N-dimethylformamide (DMF) are mixed to prepare a mixture, and this mixture is placed in a pressure jig and compression-molded to form a mixture. Then, DMF was evaporated in the same manner as in Example 1 to prepare a molded product having a thickness of 400 μm, which was a negative electrode active material layer.
The absolute value of the difference in SP value between the coating resin and the organic solvent (DMF) is 2.5.
Further, the amount of the organic solvent is 594 parts with respect to the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Example 6>
100 parts of non-graphitizable carbon powder (average particle size 20 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by EarthTechnica Co., Ltd.] and stirred at room temperature at 720 rpm, and the coating obtained in Production Example 3 was obtained. 3.0 parts of the resin solution (A'-3) for use was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 6.1 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], which is a conductive auxiliary agent, was added in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 8 hours to distill off the volatile components. .. The obtained powder was classified by a sieve having a mesh size of 212 μm to obtain a coated negative electrode active material (P-6).

100 parts of this coated negative electrode active material (P-6) and 5 parts of N, N-dimethylformamide (DMF) are mixed to prepare a mixture, and this mixture is placed in a pressure jig and compression-molded to form a mixture. Then, DMF was evaporated in the same manner as in Example 1 to prepare a molded product having a thickness of 400 μm, which was a negative electrode active material layer.
The absolute value of the difference in SP value between the coating resin and the organic solvent (DMF) is 3.4.
Further, the amount of the organic solvent is 594 parts with respect to the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Example 7>
1 part of polyvinylidene fluoride (KF polymer manufactured by Kureha Corporation, SP value is 9.1) and 99 parts of DMF, which are coating resins, are placed in a flask and heated and stirred at 120 ° C. for 10 hours for coating containing polyvinylidene fluoride. A resin solution (A'-4) was obtained.
100 parts of non-graphitizable carbon powder (average particle size 20 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by EarthTechnica Co., Ltd.], and the coating resin solution (A'-) was stirred at room temperature and 720 rpm. 4) 90.0 parts were added dropwise over 10 minutes, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 6.1 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], which is a conductive auxiliary agent, was added in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 15 hours to distill off the volatile components. .. The obtained powder was classified by a sieve having a mesh size of 212 μm to obtain a coated negative electrode active material (P-7).

100 parts of this coated negative electrode active material (P-7) and 5 parts of N, N-dimethylformamide (DMF) are mixed to prepare a mixture, and this mixture is placed in a pressure jig and compression-molded to form a mixture. Then, DMF was evaporated in the same manner as in Example 1 to prepare a molded product having a thickness of 400 μm, which was a negative electrode active material layer.
The absolute value of the difference in SP value between the coating resin and the organic solvent (DMF) is 2.9.
Further, the amount of the organic solvent is 594 parts with respect to the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Example 8>
A mixture is prepared by mixing 100 parts of the coated negative electrode active material (P-1) produced in Example 1 and 5 parts of ethanol, and this mixture is placed in a pressure jig and compression-molded to form and mold. Ethanol was evaporated and dried by allowing the product to stand in a vacuum dryer set at 80 ° C. to prepare a molded product as a negative electrode active material layer having a thickness of 400 μm.
The SP value of ethanol is 12.6, and the absolute value of the difference in SP value between the coating resin and the organic solvent (ethanol) is 2.5.
Further, the amount of the organic solvent is 594 parts with respect to the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Comparative example 1>
In Example 1, as the organic solvent to be mixed with the coated negative electrode active material, ethylene carbonate (EC) and propylene carbonate, which are the solvents of the electrolytic solution prepared in Production Example 4, were used instead of 5 parts of N, N-dimethylformamide (DMF). A mixture was prepared using 5 parts of the mixed solvent (volume ratio 1: 1) of (PC), and a molded product was prepared in the same manner as in Example 1.
The SP value of the mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC) is 14.2, and the absolute value of the difference in SP value between the coating resin and the organic solvent is 4. It is 0.1.
Further, the amount of the organic solvent is 594 parts with respect to the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Comparative example 2>
10 parts of polytetrafluoroethylene (3M Japan's Dyneon PTFE micropowder, SP value is 6.2) and 90 parts of DMF are placed in a flask, heated and stirred at 120 ° C. for 6 hours, and a coating resin solution containing polytetrafluoroethylene. (AH'-1) was obtained.
100 parts of non-graphitizable carbon powder (average particle size 20 μm) was placed in a universal mixer high-speed mixer FS25 [manufactured by EarthTechnica Co., Ltd.], and the coating resin solution (AH'-) was stirred at room temperature and 720 rpm. 1) 90.0 parts were added dropwise over 10 minutes, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 6.1 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], which is a conductive auxiliary agent, was added in 2 minutes while being divided, and stirring was continued for 30 minutes. Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 15 hours to distill off the volatile components. .. The obtained powder was classified by a sieve having a mesh size of 212 μm to obtain a coated negative electrode active material (PH-1).

100 parts of this coated negative electrode active material (PH-1) and 5 parts of N, N-dimethylformamide (DMF) are mixed to prepare a mixture, and this mixture is placed in a pressure jig and compression molded. Then, a molded product was produced in the same manner as in Example 1.
The absolute value of the difference in SP value between the coating resin solution and the organic solvent (DMF) is 5.8.
The amount of the organic solvent is 64 parts based on the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Comparative example 3>
A mixture was prepared by mixing in the same manner as in Example 1 except that 5 parts of DMF were changed to 6 parts of DMF, and this mixture was placed in a pressure jig and compression molded. The shape could not be maintained and a molded product could not be obtained. The amount of the organic solvent is 713 parts based on the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Comparative example 4>
A mixture was prepared by mixing in the same manner as in Example 1 except that 5 parts of DMF were changed to 0.3 part of DMF, and this mixture was placed in a pressure jig and compression molded, but it was taken out from the pressure jig. The mixture was unable to maintain its shape and a molded product could not be obtained. The amount of the organic solvent is 36 parts based on the total weight of 100 parts of the coating resin contained in the coating layer of the coating electrode active material.

<Shape evaluation test>
The molded products prepared in Examples 1 to 8 and Comparative Examples 1 and 2 were immersed in an electrolytic solution (electrolyte solution prepared in Production Example 4) placed in a closed container, allowed to stand in a reduced pressure environment, and in the electrolytic solution. It was visually observed whether the shape of the molded product could be maintained.
FIG. 1 is a photograph of the molded articles produced in Examples 1 to 3 and Comparative Example 1 after the shape evaluation test (1 month after immersion in the electrolytic solution).
The molded product of Comparative Example 1 began to lose its shape immediately during the depressurization operation, and could hardly maintain its shape after 1 hour. On the other hand, the molded articles of Examples 1 to 3 did not lose their shape at room temperature for 1 month or more, and could maintain their shape.
The molded products of Examples 4 to 8 did not lose their shape at room temperature for 1 month or more and could retain their shape, and the molded products of Comparative Example 2 could hardly maintain their shape after 1 hour.
Good shape retention in the electrolytic solution means that the shape retention of the electrode active material layer after the electrolytic solution is injected into the battery container is excellent. If the shape-retaining property of the electrode active material layer is excellent, defects in the electrode active material layer are unlikely to occur and internal resistance does not increase, so that the electrode can be made into an electrode having excellent cycle characteristics.

The method for manufacturing an electrode for a lithium ion battery of the present invention is, in particular, a method for manufacturing an electrode for a lithium ion battery used for manufacturing a lithium ion secondary battery used for a mobile phone, a personal computer, a hybrid vehicle, an electric vehicle, and the like. It is useful as.

Claims (5)

A method for manufacturing an electrode for a lithium ion battery, which has an electrode active material layer containing a coated electrode active material having a coating layer containing a coating resin on at least a part of the surface of the electrode active material that occludes and releases lithium ions. hand,
It has a step of molding a mixture containing the coated electrode active material and an organic solvent.
The amount of the organic solvent contained in the mixture is 50 to 600 parts with respect to 100 parts of the total weight of the coating resin contained in the coating layer of the coating electrode active material.
A method for manufacturing an electrode for a lithium ion battery, wherein the absolute value of the difference between the solubility parameter of the organic solvent and the solubility parameter of the coating resin is 1.5 to 4. The method for producing an electrode for a lithium ion battery according to claim 1, wherein the organic solvent is N, N-dimethylformamide. The coating resin comprises a group consisting of a monomer (a1) having a carboxyl group or an acid anhydride group and an unsaturated double bond, a monomer (a2) represented by the following general formula (1), vinylidene fluoride and acrylonitrile. The method for producing an electrode for a lithium ion battery according to claim 1 or 2, which is a polymer (A1) of a monomer composition containing at least one selected.
CH ₂ = C (R ¹ ) COOR ² (1)
[In the formula (1), R ¹ is a hydrogen atom or a methyl group, and R ² is a straight chain having 4 to 12 carbon atoms or a branched alkyl group having 3 to 36 carbon atoms. ] Any of claims 1 to 3 in which the weight ratio of the electrode active material to the coating resin in the coated electrode active material is electrode active material / coating resin = 90 / 10-99.99 / 0.01. The method for manufacturing an electrode for a lithium ion battery described in. The method for manufacturing an electrode for a lithium ion battery according to any one of claims 1 to 4, wherein the electrode active material layer has a thickness of 150 μm or more.

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