KR102054737B1 - Positive electrode paste for cell - Google Patents

Abstract

The battery positive electrode paste which can shorten the drying time of a positive electrode mixture, without impairing coating property and the adhesiveness of a positive electrode mixture is provided. A positive electrode active material, a conductive agent, a solvent, and a copolymer are included, and the copolymer contains structural units of two specific structures.

Description

Battery positive electrode paste {POSITIVE ELECTRODE PASTE FOR CELL}

The present invention relates to a battery positive electrode paste.

The positive electrode for nonaqueous electrolyte batteries manufactures the positive electrode paste which disperse | distributed the positive electrode active material, the electrically conductive agent, and the binder in a solvent, apply | coats it continuously to the electrical power collectors, such as aluminum foil, and passes through the inside of a drying furnace, and volatilizes a solvent. It is manufactured. When the line speed of this electrode plate application | coating process is made high, since the time which a pole plate stays in a drying furnace becomes short, drying shortage arises.

In order to avoid this, a method of increasing the drying rate by increasing the temperature or air volume in the drying furnace is considered, but rapid drying lowers the adhesiveness of the positive electrode mixture layer or, if an organic solvent is used, the flammable gas concentration in the drying furnace. The problem arises that is too high.

Alternatively, a method of securing a residence time in the drying furnace by enlarging and drying the drying furnace is considered, but a problem arises in that a large amount of equipment investment is required.

As a method other than the above, it is considered that it is possible to shorten the drying time by increasing the mass ratio (hereinafter, the paste solid content) of the solids in the positive electrode paste, that is, by reducing the content of the solvent. However, in this case, since the viscosity of a paste increases, there exists a problem that coating property falls, for example, a breakage generate | occur | produces.

Patent Literature 1 discloses that dispersibility of the positive electrode paste can be improved by reducing the viscosity of the positive electrode paste by chemically bonding a monomer to the surface of the conductive agent, followed by heat polymerization and using the same for the positive electrode paste. However, in order to chemically bond the polymer to the surface of the conductive agent, it is generally thought that it is complicated and requires a process of several steps of the chemical reaction with respect to the conductive agent having poor handling with fine powder.

Patent Literature 2 shows that the dispersibility of the conductive agent in the positive electrode paste can be improved by adding a surfactant. However, before adding a conductive agent, it is essential to add a dispersant and to stir, whereby a plurality of kneading operations are performed, whereby a decrease in production efficiency is concerned.

Patent Document 3 describes that a dispersant is used to improve the fluidity of the positive electrode paste containing a large amount of a conductive agent having a large specific surface area. However, the comparative data which made clear the effect of viscosity reduction by this is not shown. In addition, there is only one type of dispersant used here, and it is unclear whether a viscosity reducing effect is obtained in all dispersants.

Japanese Patent Laid-Open No. 2002-100360 Japanese Patent Laid-Open No. 2002-151057 Japanese Patent Laid-Open No. 2005-197073

An object of this invention is to provide the battery positive electrode paste with high solid content which can shorten the drying time of a positive electrode mixture, without impairing the applicability | paintability of a positive electrode paste and the adhesiveness of the positive electrode mixture after application | coating.

MEANS TO SOLVE THE PROBLEM As a result of various examination, when the copolymer which has a specific structure as a dispersing agent is used, it is large in adhesiveness of the viscosity reduction effect of a positive electrode paste, and the adhesive material layer of the positive electrode obtained by apply | coating positive electrode paste by the difference of the structure. I found a car.

The constitution effect of this invention is demonstrated through technical idea. However, the mechanism is included in the estimation, and the right or wrong does not limit the present invention. In addition, this invention can be implemented in other various forms, without deviating from the mind or main characteristic. Therefore, embodiment or experimental example mentioned later is only a mere illustration at all points, and should not interpret it limitedly. In addition, all the deformation | transformation and a change which belong to the equal range of a claim are within the scope of this invention.

1st invention is a battery positive electrode paste containing a positive electrode active material, a electrically conductive agent, a solvent, and a copolymer, The said copolymer is represented by the structural unit (a) represented by following General formula (1), and following General formula (2) It is a battery positive electrode paste which is a copolymer containing a structural unit (b).

(In formula, R <^1> , R <^2> , R <^3> , R <^5> , R <^6> , R <^7> and R <^9> are the same or different, and represent a hydrogen atom, a methyl group, or an ethyl group, and R <^4> is a C8-C30 hydrocarbon group. R ⁸ represents a straight or branched alkylene group having 2 to 4 carbon atoms, X ¹ and X ² represent an oxygen atom or NH, and p represents a number of 1 to 50).

According to this invention, it is possible to provide the battery positive electrode paste with high solid content which can shorten the drying time of a positive electrode mixture, without impairing the applicability | paintability of a positive electrode paste and the adhesiveness of the positive electrode mixture after application | coating.

1 is a graph showing the relationship between the amount of copolymer added and paste viscosity.

The present invention provides a paste containing a positive electrode active material, a conductive agent, a solvent and a copolymer containing a structural unit (a) represented by the general formula (1) and a structural unit (b) represented by the general formula (2). By using it for manufacture of a positive electrode, the knowledge that it is possible to provide the battery positive electrode paste with high solid content which can shorten the drying time of a positive electrode mixture without impairing the applicability | paintability of a positive electrode paste and the adhesiveness of the positive electrode mixture after application | coating is possible. Based on.

Although the mechanism detail of the effect expression of this invention is not clear, the applicant estimates as follows. When the solid content of a positive electrode paste is made high, it is thought that the positive electrode active material and electrically conductive agent particle in a paste aggregate, form a network three-dimensionally, and thicken. As for the copolymer contained in the battery positive electrode paste of this invention, the structural unit (a) which has a hydrophobic group adsorb | sucks firmly to the surface of the particle | grains of a positive electrode active material or a conductive agent in a paste, and the structural unit (b) which has a polyoxyalkylene group is By causing a strong three-dimensional repulsive force between particles, it is thought that the effect of suppressing aggregation of the particles in the paste is reduced and the viscosity of the paste is lowered.

On the other hand, in order to produce a positive electrode, although a positive electrode paste needs to maintain favorable adhesiveness with aluminum foil etc. which are positive electrode collectors, since a dispersing agent acts on the interface of a positive electrode collector and a positive electrode mixture normally, adhesiveness falls. However, in the present invention, the copolymer has a dispersibility because the copolymer is firmly adsorbed on the surface of the particles of the positive electrode active material or the conductive agent in the paste by the structural unit (a), and the solubility of the copolymer in the solvent is controlled. It is suppressed that bleeding out to the positive electrode collector interface, adhesiveness becomes favorable, and positive electrode mixture peeling strength also becomes favorable. However, these are estimation and this invention is not limited to these mechanisms.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described concretely.

[Copolymer]

The copolymer used for this invention contains the structural unit (a) represented by the said General formula (1), and the structural unit (b) represented by the said General formula (2).

In the formula (1), R ¹ and R ² are preferably a hydrogen atom, and R ³ is a hydrogen atom or the like from the viewpoint of the viscosity reduction effect of the positive electrode paste and the ease of introduction of the structural unit (a) into the copolymer. A methyl group is preferable and a methyl group is more preferable. From the viewpoint of the viscosity reduction effect of the positive electrode paste and the maintenance of the positive electrode mixture peel strength, R ⁴ is preferably an alkyl group or an alkenyl group, and from the same viewpoint, the carbon number of R ⁴ is 8 or more, preferably 10 or more, and 12 or more. More preferably, from the same viewpoint, 26 or less are preferable, 22 or less are more preferable, and 20 or less are still more preferable. Putting these viewpoints together, 8-26 are preferable, as for carbon number of R <^4> , 10-22 are more preferable, and 12-20 are more preferable. Specific examples of R ⁴ include an octyl group, 2-ethylhexyl group, decyl group, lauryl group, myristyl group, cetyl group, stearyl group, oleyl group and behenyl group. From the viewpoint of ease of introduction of the structural unit (a) into the copolymer, X ¹ is preferably an oxygen atom.

In synthesize | combining the copolymer used for this invention, as a specific example of the monomer (henceforth a monomer (a)) which gives the said structural unit (a), 2-ethylhexyl (meth) acrylate and octyl (meth) Ester compounds such as acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, and behenyl (meth) acrylate; Amide compounds, such as 2-ethylhexyl (meth) acrylamide, octyl (meth) acrylamide, lauryl (meth) acrylamide, stearyl (meth) acrylamide, and behenyl (meth) acrylamide, are mentioned. Among them, lauryl (meth) acrylate, stearyl (meth) acrylate and behenyl (meth) acrylate from the viewpoint of the viscosity reduction effect of the positive electrode paste and the ease of introduction of the structural unit (a) into the copolymer. desirable. Among these monomers, one kind or two or more kinds can be used.

5 mass% or more is preferable from a viewpoint of the viscosity reduction effect of a positive electrode paste, and a positive electrode mixture peeling strength maintenance, and, as for the ratio of the structural unit (a) which occupies for the copolymer used for this invention, 10 mass% or more is more preferable. , 15 mass% or more is more preferable. Moreover, from a similar viewpoint, 90 mass% or less is preferable, 85 mass% or less is more preferable, 80 mass% or less is more preferable, and 72 mass% or less is still more preferable. Putting these viewpoints together, 5-90 mass% is preferable, as for the ratio of the structural unit (a) which occupies for the copolymer used for this invention, 10-85 mass% is more preferable, 15-80 mass% is further Preferably, 15-72 mass% is more preferable.

In the general formula (2), in view of the introduction of ease of structural units (b) of the positive electrode paste of the positive electrode active material and improved dispersion of the conductive agent and the copolymer, R ⁵ and R ⁶ are hydrogen atoms are preferred and, R ⁷ And R ⁹ is preferably a hydrogen atom or a methyl group, and more preferably a methyl group. From the same viewpoint, R ⁸ is preferably an ethylene group or a propylene group, and more preferably an ethylene group. From a viewpoint of the viscosity reduction effect of a positive electrode paste, and the ease of introduction of the structural unit (b) to a copolymer, 1 or more is preferable, as for p, 2 or more are more preferable, and 3 or more are more preferable. Moreover, from a similar viewpoint, 50 or less are preferable, 35 or less are more preferable, and 20 or less are more preferable. In total, 1 to 50 are preferable, as for p, 2 to 35 are more preferable, and 3 to 20 are more preferable. From the viewpoint of ease of introduction of the structural unit (b) into the copolymer, X ² is preferably an oxygen atom.

As a structural unit (b), the structure derived from a nonionic monomer, the structure which introduce | transduced the nonionic group after superposition | polymerization, etc. are mentioned.

In synthesizing the copolymer used in the present invention, as a monomer (hereinafter, also referred to as monomer (b)) to impart the structural unit (b), methoxy polyethylene glycol (meth) acrylate and methoxy poly (ethylene glycol / Propylene glycol) mono (meth) acrylate, ethoxy poly (ethylene glycol / propylene glycol) mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, 2-meth Methoxyethyl (meth) acrylamide, 2-ethoxyethyl (meth) acrylamide, 3-methoxypropyl (meth) acrylamide, and the like.

As a structural unit (b), the monomer represented by following General formula (3) from a viewpoint of the dispersibility improvement of a positive electrode active material and a conductive agent in a positive electrode paste is preferable.

^{(R 5, R 6, R} 7 and R ⁹ in the formula are the same or different and are a hydrogen atom, a methyl group or an ethyl group, R ⁸ represents an alkylene group of a straight-chain or branched having 2 to 4, X ² Represents an oxygen atom or NH, p represents a number from 1 to 50)

In the formula (3), R ⁵ and R ⁶ are preferably hydrogen atoms from the viewpoint of improving the dispersibility of the positive electrode active material and the conductive agent in the positive electrode paste and the ease of introduction of the structural unit (b) into the copolymer, and R ⁷ is preferably R ^7. And R ⁹ is preferably a hydrogen atom or a methyl group, and more preferably a methyl group. From the same viewpoint, R ⁸ is preferably an ethylene group or a propylene group, and more preferably an ethylene group. From a viewpoint of the viscosity reduction effect of a positive electrode paste, and the ease of introduction of the structural unit (b) to a copolymer, 1 or more is preferable, as for p, 2 or more are more preferable, and 3 or more are more preferable. Moreover, from a similar viewpoint, 50 or less are preferable, 35 or less are more preferable, and 20 or less are more preferable. In total, 1 to 50 are preferable, as for p, 2 to 35 are more preferable, and 3 to 20 are more preferable. From the viewpoint of ease of introduction of the structural unit (b) into the copolymer, X ² is preferably an oxygen atom.

Among these monomers, one kind or two or more kinds can be used.

10 mass% or more is preferable from a viewpoint of the viscosity reduction effect of a positive electrode paste, and a positive electrode mixture peeling strength maintenance, and, as for the ratio of the structural unit (b) which occupies for the copolymer used for this invention, 15 mass% or more is more preferable. , 20 mass% or more is more preferable, and 23 mass% or more is more preferable. Moreover, from a similar viewpoint, 85 mass% or less is preferable, 80 mass% or less is more preferable, 75 mass% or less is more preferable. Putting these viewpoints together, 10-85 mass% is preferable, as for the ratio of the structural unit (b) which occupies for the copolymer used for this invention, 15-80 mass% is more preferable, 20-75 mass% is further Preferably, 23-75 mass% is more preferable.

The mass ratio (structural unit (a) / structural unit (b)) of the structural unit (a) and the structural unit (b) contained in the copolymer of the present invention is in view of the effect of reducing the viscosity of the positive electrode paste and maintaining the positive electrode mixture peel strength. , 0.1 or more is preferable, and 0.2 or more is more preferable. Moreover, 10.0 or less are preferable from a similar viewpoint, 5.4 or less are more preferable, 4.0 or less are more preferable, and 3.2 or less are more preferable. In summary, the mass ratio (structural unit (a) / structural unit (b)) of the structural unit (a) and the structural unit (b) included in the copolymer of the present invention is preferably 0.1 to 10.0, and 0.2 to 5.33 are more preferred, 0.2 to 4.0 are more preferred, and 0.2 to 3.2 are even more preferred.

The copolymer used for this invention can have structural units (c) other than the said structural unit (a) and the said structural unit (b). In synthesize | combining the copolymer used for this invention, if the monomer which gives a structural unit (c) (henceforth a monomer (c)) can be copolymerized with monomer (a) or monomer (b), there will be no restriction | limiting in particular, 1 type, or 2 or more types can be used.

Examples of the monomer (c) include acid monomers such as (meth) acrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, and (meth (Meth) acrylic acid esters, such as benzyl acrylate, cyclohexyl (meth) acrylate, isoboroyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, and dimethylaminoethyl (meth) acrylate; (Meth) acrylamides, such as (meth) acrylamide, dimethyl (meth) acrylamide, isopropyl (meth) acrylamide, and tert-butyl (meth) acrylamide; Styrenes such as styrene and p-methyl styrene and vinyl esters such as vinyl acetate; Vinyl pyridines such as 2-vinylpyridine; Vinyl pyrrolidones, such as vinyl pyrrolidone, etc. are mentioned.

In the copolymer of the present invention, the total content of the structural unit (a) and the structural unit (b) is preferably 40 mass% or more from the viewpoint of the viscosity reduction effect of the positive electrode paste and the maintenance of the positive electrode mixture peel strength, and 60 mass% The above is more preferable, 80 mass% or more is more preferable, 90 mass% or more is more preferable, 95 mass% or more is more preferable.

As for the ratio of the structural unit (c) which occupies for the copolymer used for this invention, 0-60 mass% is preferable from a viewpoint of the viscosity reduction effect of a positive electrode paste, and maintenance of positive electrode mixture peeling strength, and 0-40 mass% is more preferable. 0-30 mass% is more preferable, 0-20 mass% is still more preferable, 0-10 mass% is more preferable, 0-5 mass% is still more preferable. When the ratio of a structural unit (c) is 60 mass% or less, content in the paste of a structural unit (a) and a structural unit (b) is ensured, and the viscosity reduction effect of a positive electrode paste becomes higher.

In the battery positive electrode paste of the present invention, the content of the copolymer is preferably 0.02% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, from the viewpoint of the viscosity reduction effect of the positive electrode paste. 0.2 mass% or more is more preferable. Moreover, from a viewpoint of maintaining battery output, 1 mass% or less is preferable, 0.8 mass% or less is more preferable, 0.6 mass% or less is more preferable, 0.5 mass% or less is still more preferable. In summary, the content of the copolymer in the battery positive electrode paste of the present invention is preferably from 0.02 to 1 mass%, more preferably from 0.05 to 0.8 mass%, still more preferably from 0.1 to 0.6 mass%, 0.2-0.5 mass% is more preferable.

0.5 mass parts or more are preferable with respect to 100 mass parts of said conductive agents from a viewpoint of the viscosity reduction effect of a positive electrode paste, and, as for content of the said copolymer in the battery positive electrode paste of this invention, 1.5 mass parts or more are more preferable. 3 mass parts or more are more preferable, and 6 mass parts or more are more preferable. Moreover, from a viewpoint of maintaining battery output, 35 mass parts or less are preferable with respect to 100 mass parts of said electrically conductive agents, 30 mass parts or less are more preferable, 25 mass parts or less are more preferable, 20 mass parts or less are more preferable More preferred. In summary, the content of the copolymer in the battery positive electrode paste of the present invention is preferably 0.5 to 35 parts by mass, more preferably 1.5 to 30 parts by mass, still more preferably 3 to 25 parts by mass, 6 20 mass parts is more preferable.

In the battery positive electrode paste of the present invention, the total of the content of the structural unit (a) and the structural unit (b) contained in the copolymer with respect to 100 parts by mass of the conductive agent is in view of the viscosity reduction effect of the positive electrode paste. 0.5 mass part or more is preferable, 1 mass part or more is more preferable, 2 mass parts or more are more preferable, 5 mass parts or more are still more preferable. Moreover, from a viewpoint of maintaining battery output, 30 mass parts or less are preferable, 25 mass parts or less are more preferable, 20 mass parts or less are more preferable, 15 mass parts or less are still more preferable. In summary, in the battery positive electrode paste of the present invention, the total of the content of the structural unit (a) and the structural unit (b) included in the copolymer with respect to 100 parts by mass of the conductive agent is 0.5 to 30. A mass part is preferable, 1-25 mass parts is more preferable, 2-20 mass parts is more preferable, 5-15 mass parts is still more preferable.

The synthesis | combining method of the copolymer of this invention is not specifically limited, The method used for superposition | polymerization of normal (meth) acrylic acid ester is used. For example, it is a free radical polymerization method, a living radical polymerization method, an anion polymerization method, a living anion polymerization method. For example, when using the free radical polymerization method, it can obtain by a well-known method, such as polymerizing the monomer component containing a monomer (a) and a monomer (b) by the solution polymerization method.

As a solvent used for solution polymerization, hydrocarbon (hexane, heptane), aromatic hydrocarbon (toluene, xylene, etc.), lower alcohol (ethanol, isopropanol, etc.), ketone (acetone, methyl ethyl ketone), ether (tetrahydro) Organic solvents, such as furan, diethylene glycol dimethyl ether), and N-methylpyrrolidone, can be used. The amount of solvent is preferably 0.5 to 10 times the mass ratio with respect to the whole monomer.

Although a well-known radical polymerization initiator can be used as a polymerization initiator, an azo type polymerization initiator, hydro peroxides, dialkyl peroxides, diacyl peroxide, ketone peroxide etc. are mentioned, for example. 0.01-5 mol% is preferable with respect to monomer component whole quantity, 0.01-3 mol% is more preferable, and its 0.01-1 mol% is especially preferable. It is preferable to perform a polymerization reaction at the temperature range of 60-180 degreeC under nitrogen stream, and the reaction time of 0.5 to 20 hours is preferable.

Moreover, a well-known chain transfer agent for adjusting molecular weight can be used. For example, mercapto compounds, such as isopropyl alcohol and mercaptoethanol, are mentioned.

In the copolymer of the present invention, the arrangement of the structural unit (a) and the structural unit (b) may be any of random, block or graft. Moreover, you may contain structural units other than these structural units.

 From the viewpoint of maintaining the positive electrode mixture peel strength, the weight average molecular weight of the copolymer is preferably 9000 or more, more preferably 1.50,000 or more, still more preferably 30,000 or more, and even more preferably 50,000 or more. Moreover, from a viewpoint of the viscosity reduction effect of a positive electrode paste, 1 million or less are preferable, 800,000 or less are more preferable, 600,000 or less are more preferable, and 500,000 or less are still more preferable. In summary, the weight average molecular weight of the copolymer is preferably from 90,000 to 1 million, more preferably from 1.50,000 to 800,000, still more preferably from 30,000 to 600,000, and even more preferably from 4.50,000 to 500,000. In addition, a weight average molecular weight is the value measured by GPC (gel permeation chromatography), and the detail of measurement conditions is as showing in an Example.

In the positive electrode paste of this invention, you may contain dispersing agents other than the said copolymer. In the positive electrode paste of this invention, 40 mass% or more is preferable, as for content of the said copolymer with respect to the sum total of the said copolymer and dispersing agents other than the said copolymer, 60 mass% or more is more preferable, 80 mass% The above is more preferable, and 100 mass% is more preferable.

[Positive electrode active material]

There is no restriction | limiting in particular if it is an inorganic compound, For example, the compound and lithium transition metal complex oxide which have an olivine structure can be used. As a compound having an olivine structure, a compound represented by the general formula Li _x M1 _s PO ₄ (wherein M1 is a 3d transition metal, 0 ≦ _x ≦ 2, 0.8 ≦ s ≦ 1.2) can be exemplified. You may coat and use amorphous carbon etc. to the compound which has an olivine structure. As the lithium transition metal composite oxide, lithium manganese oxide having a spinel structure, a lithium having a layered structure and represented by the general formula Li _x MO _{2 -δ} (wherein M is a transition metal, 0.4≤x≤1.2, 0≤δ≤0.5) And transition metal composite oxides. As said transition metal M, Co, Ni, or Mn can be included. The lithium transition metal composite oxide may further contain one or two or more elements selected from Al, Mn, Fe, Ni, Co, Cr, Ti, Zn, P, and B.

[Challenge]

As the conductive agent, it is preferable to use a carbon-based conductive agent. As the carbon-based conductive agent, carbon black such as acetylene black, furnace black, Ketjen black, graphite and the like can be used. You may use conductive polymers other than carbon system, such as polyaniline.

[Binder]

As the binder, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, polyacrylonitrile, or the like can be used alone or in combination.

[Positive electrode paste]

A positive electrode paste mixes, stirs, and prepares the above-mentioned copolymer, a positive electrode active material, a conductive agent, a binder, a solvent for solid content adjustment, and the like. In addition, you may add a dispersing agent, a functional material, etc. As the solvent, non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO) or water can be used. In addition, in the positive electrode paste of this invention, it is preferable to use a non-aqueous solvent, and it is more preferable to use NMP especially.

A planetary mixer, a bead mill, a jet mill, etc. can be used for mixing and stirring. Moreover, these can also be used together.

At the time of material input, you may input while rotating a stirring blade. Thereby, it is possible to suppress the mechanical load of a stirring apparatus, to suppress the material volume in a stirring container, and to premix each material. Moreover, you may divide and input into multiple times, without putting all the quantity. Thereby, the mechanical load of a stirring apparatus can be suppressed.

The copolymer of the present invention may be used after being dissolved in a non-aqueous solvent or a solvent such as water in advance, even if used as a solid. According to Patent Literature 2, in order to avoid aggregation of fluorinated binders by fibrosis, it is essential to add the dispersing agent before adding the binder. However, in the copolymer according to the present invention, a solvent in the positive electrode paste and Since the affinity of the binder component is very high, it may be thrown in any step during the kneading step, and it is also possible to knead a plurality of times before and after copolymer addition. For example, by injecting a copolymer early in the kneading step, the viscosity of the paste is lowered, the mechanical load and the required energy of the kneading device are reduced, and the solid content of the paste can be made higher. When the copolymer is added at the end of the kneading process or just before the completion of the paste, in the kneading process until the copolymer is mixed, the paste viscosity is maintained high and a strong shear stress is applied to the paste, whereby the dispersion state of the paste It is preferable because it improves. Thus, in order to obtain the target paste, the copolymer of this invention can be thrown in at the arbitrary stage of a kneading process. Moreover, since only a powder component, such as a positive electrode active material and a electrically conductive agent, may be mixed at the same time, it may generate a lump, and you may introduce | transduce at the stage where each material became a paste state. For example, you may inject with a binder or a solvent before putting a powdery material, or after mixing some or all of a binder or a solvent with a powdery material. Or you may mix previously with the solution of a binder.

[Positive electrode]

A positive electrode coats the said positive electrode paste on electrical power collectors, such as aluminum foil, and produces it by drying it. In order to raise the density of a positive electrode, you may perform compaction with a press.

A die head, a comma reverse roll, a direct roll, a gravure roll, etc. can be used for application | coating of a positive electrode paste. Drying after application | coating can be performed individually or in combination with heating, airflow, infrared irradiation, etc.

Pressing of a positive electrode can be performed by a roll press machine etc.

Example

Hereinafter, although the Example and comparative example of this invention are shown, this invention is not limited to this.

The detail of the copolymer and homopolymer used for the following example and the comparative example is shown to Tables 1-6. Here, the symbol of the raw material used for the Tables 1-6 and the following Examples is as follows.

LMA: Lauryl methacrylate (manufactured by Mitsubishi Gas Chemical Co., Ltd., product number: GE-410) (R ⁴ : C ₁₂ H ₂₅ )

SMA: Stearyl methacrylate (manufactured by Shinnakamura Chemical Co., Ltd., product number: NK-ester S) (R ⁴ : C ₁₈ H ₃₇ )

BHMA: Behenyl methacrylate (manufactured by Shinnakamura Chemical Co., Ltd., product number: NK-ester BH) (R ⁴ : C ₂₂ H ₄₅ )

PEG (2) MA: Methoxypolyethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product number: NK-ester M-20G, average added mole number of ethylene oxide p: 2)

PEG (9) MA: Methoxypolyethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product number: NK-ester M-90G, average added mole number of ethylene oxide p: 9)

PEG (23) MA: methoxy polyethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product number: NK-ester TM-230G, average added mole number of ethylene oxide p: 23)

MAA: Methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.)

MPD: 3-mercapto-1,2-propanediol (manufactured by Wako Pure Chemical Industries, Ltd.)

N-DM: dodecyl mercaptan (manufactured by Toyo Chemical Co., Ltd.)

NMP: N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.)

Hexane: n-hexane (manufactured by Wako Pure Chemical Industries, Ltd.)

V-65B: 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)

Synthesis Example 1 of Copolymer

As a "initial monomer solution for initial injection," a mixed solution containing 3 g of SMA, 14 g of PEG (23) MA, 3 g of MAA, and 17 g of NMP was prepared. As a "dropping monomer liquid," a mixed solution containing 27 g of SMA, 126 g of PEG (23) MA, 27 g of MAA, and 153 g of NMP mixed liquid was prepared. As a "initiator liquid," a mixed solution containing 0.6 g of V-65B and 3 g of NMP was prepared. As a "dropping initiator liquid," a mixed solution containing 5.4 g of V-65B and 27 g of NMP was prepared.

Into the separable flask (reactor) provided with a reflux tube, a stirring device, a thermometer, and a nitrogen introduction tube, the entire amount of the "initial unit monomer solution" is introduced, nitrogen is replaced in the reactor, and the temperature in the tank (the temperature of the input raw material) ) Was heated to 65 ° C. After the temperature in the tank reached 65 ° C, the entire amount of the "initiator liquid" was added to the tank while the tank was stirred. Subsequently, the said "dropping monomer liquid" and the "dropping initiator liquid" were dripped at the same time over 3 hours. After completion of dropping, the mixture was further stirred at 65 ° C for 1 hour. Subsequently, the temperature in the tank was raised to 75 ° C. over about 30 minutes while the stirring was continued, and after the temperature was raised, the inside of the tank was further stirred for 2 hours. Subsequently, the tank internal temperature was cooled to 40 degrees C or less in the water bath. In order to adjust concentration, NMP was added and mixed in the tank and the NMP solution of copolymer A was obtained. The non volatile matter of the copolymer A solution was 40 mass%, and the weight average molecular weight of copolymer A was 55000.

Synthesis Example 2 of Copolymer

It is the same as that of the synthesis example 1 of the said copolymer except the composition of the "initial monomer liquid for initial injection", the "monomer for dropping", the "initiator liquid", and the "dropping initiator liquid" was changed according to description of Table 1, respectively. By the method, copolymers B to AE were synthesized. In addition, in the synthesis | combination of copolymer H, J, K, and AE, the batch polymerization method which initially injected all the monomers and all the initiators was employ | adopted.

Synthesis Example of Single Polymer

Into a separable flask (reactor) provided with a reflux tube, a stirring device, a thermometer, and a nitrogen inlet tube, a total amount of a mixed solution (monomer solution for initial charge) containing 200 g of SMA and 180 g of hexane was added, and the inside of the reactor was filled with nitrogen. Substituted and heated the tank internal temperature (injection raw material temperature) to 65 degreeC. After the temperature in the tank reached 65 ° C, a mixed solution (initiator solution) containing 2.2 g of V-65B and 20 g of hexane was added while stirring the inside of the tank. Furthermore, after stirring the inside of a tank at 65 degreeC for 5 hours, the tank internal temperature was cooled to 40 degrees C or less in the water bath. To the hexane solution of the obtained homopolymer Q, ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) having a volume ratio of 10 times was placed in a beaker, and the solution of the obtained homopolymer Q was added dropwise into the beaker while stirring the inside of the beaker. The precipitated solid was separated by filtration and dried at 10 Pa and 80 ° C for 12 hours in a reduced pressure drier to obtain homopolymer Q. The weight average molecular weight of homopolymer Q was 69000. 90 g of NMP was added to the obtained 10 g of homopolymer Q and stirred at 80 ° C. for 30 minutes. However, since it was not dissolved, a positive electrode paste using homopolymer Q could not be produced.

[Measurement of Nonvolatile Matter]

The nonvolatile content of the copolymer solution was measured as follows. 10 g of dry anhydrous sodium sulfate and a glass rod are put into a chaale, and the total mass thereof is measured to be W ₃ (g). In addition, 2 g of NMP solutions of the copolymers obtained in Synthesis Examples 1 and 2 of the copolymer as a sample are placed in this chaale, and the total mass thereof is measured to be W ₁ (g). In Shaale, dry anhydrous sodium sulfate and the sample are mixed with the glass rod, and in Shaale, dry anhydrous sodium sulfate and the sample and the glass rod mixed with the glass rod are put at 140 ° C. under reduced pressure dryer (under nitrogen stream, pressure 40 Iii) Dry the entire Shale for 12 hours. By measuring the total mass after drying of Petri dish, and the W ₂ (g). The value obtained by following Formula was called non volatile matter.

Nonvolatile matter (mass%) = 100- (W ₁ -W ₂ ) / (W ₁ -W ₃ ) × 100

[Measurement of Weight Average Molecular Weight of Copolymer and Homopolymer]

The weight average molecular weight of the copolymer was measured by the GPC method. Detailed conditions are as follows.

Measuring device: HLC-8320GPC (manufactured by Tosoh Corporation)

Column: α-M + α-M (manufactured by Tosoh Corporation)

Column temperature: 40 ℃

Detector: Differential Refractive Index

Eluent: N, N-dimethylformamide (DMF) solution of 60 mmol / L H ₃ PO ₄ and 50 mmol / L LiBr

Flow rate: 1ml / min

Standard samples used for the calibration curve: Monodisperse polystyrene manufactured by Tosoh Corporation 5.26 × 10 ² , 1.02 × 10 ⁵ , 8.42 × 10 ⁶ ; Nishi-Go-Kyo Monodispersed Polystyrene 4.0 × 10 ³ , 3.0 × 10 ⁴ , 9.0 × 10 ⁵ (numbers are each molecular weight)

Sample solution: DMF solution containing 0.5 wt% solids of copolymer

Injection volume of sample solution: 100 μl

However, about the copolymer O, P, AB, AC, AD, AE, and homopolymer Q, since it did not melt | dissolve in DMF, the following conditions were employ | adopted.

Measuring device: HLC-8220GPC (manufactured by Tosoh Corporation)

Column: GMHXL + GMHXL (Tosoh Corporation)

Column temperature: 40 ℃

Detector: Differential Refractive Index

Eluent: 50mmol tetrahydrofuran (THF) solution of LCH ₃ COOH

Flow rate: 1ml / min

Standard samples used for the calibration curve: Monodisperse polystyrene manufactured by Tosoh Corporation 5.26 × 10 ² , 1.02 × 10 ⁵ , 8.42 × 10 ⁶ ; Nishi-Go-Kyo Monodispersed Polystyrene 4.0 × 10 ³ , 3.0 × 10 ⁴ , 9.0 × 10 ⁵ (numbers are each molecular weight)

Sample solution: THF solution containing 0.2wt% solids of copolymer or homopolymer

Injection volume of sample solution: 100 μl

[Production and Evaluation of Positive Electrode Paste and Positive Electrode]

The symbol of the material used for the positive electrode paste which concerns on a following example and a comparative example is as follows.

· LiMO _2: lithium-transition metal composite oxide, the _{composition: LiNi 1/3 Mn 1/} 3 Co 1/3 O 2 (D50: 6.5㎛, BET specific surface area: 0.7㎡ / g)

LiMn ₂ O ₄ : lithium manganese oxide, composition: LiMn ₂ O ₄ (D50: 18 μm, BET specific surface area: 0.2 m 2 / g)

LiFePO ₄ : lithium iron phosphate, composition: LiFePO ₄ (D50: 10 μm, BET specific surface area: 10.5 m 2 / g)

Powdered product: Acetylene black (Denki Chemical Co., Ltd. make, product name: Denka black powdered product)

FX35: Acetylene black (manufactured by Denki Chemical Co., Ltd., product name: Denka Black FX-35)

HS100: Acetylene black (manufactured by Denki Chemical Co., Ltd., product name: Denka Black HS-100)

[Production of Positive Electrode Paste]

The positive electrode paste was produced using the copolymer shown in Tables 2-5, a positive electrode active material, a electrically conductive agent, and polyvinylidene fluoride (PVDF) as a binder, and NMP as a non-aqueous solvent. In Tables 7 to 9 and 11, a 12% NMP solution of Kureha Co. # 1100 was used as the PVDF, and in Table 10, an 8% NMP solution of Arkema Co., Ltd. Garner HSV900 was used as the PVDF. In addition, the mass ratio of the positive electrode active material, the binder, and the conductive agent was set to 90: 5: 5 (solid content conversion). The positive electrode paste was produced through the kneading process using a multi blender mill by adjusting solid content (mass%) by adjusting the quantity of the said non-aqueous solvent. Here, solid content (mass%) of a positive electrode paste is solid content mass% of the material containing the copolymer, a positive electrode active material, a electrically conductive agent, and a binder which a positive electrode paste contains.

[Measurement of Viscosity of Positive Electrode Paste]

The viscosity of the positive electrode paste was measured using a rheometer. Reo Stress 6000 manufactured by HAAKE Corporation was used as the measuring device for the rheometer, and a parallel plate having a diameter of 35 mm was used as the measuring rotor. The measurement temperature was 25 degreeC, and the sequence which measured the path | route from the shear rate 0.0001s ^-1 to 1000s- ¹ and the return route from 1000s- ¹ to 0.0001s- ¹ over successive 200 seconds was implemented. As a representative value of the viscosity, the value at the shear rate of 10s ⁻¹ of the air path was defined as the paste viscosity.

For each Example, except that the copolymer of the present invention was not added, the viscosity of the positive electrode paste according to the corresponding comparative example having the same composition was defined as "paste viscosity R", and in the following formula, the viscosity was reduced by addition of the copolymer. The reduction rate was calculated and the effect was compared.

Viscosity reduction rate (%) = {([paste viscosity R]-[paste viscosity]) / (paste viscosity R)} x 100

The results of the viscosity and the viscosity reduction rate are shown in Tables 7 to 10.

[Coatingability Test of Positive Electrode Paste]

In this test, the gap of the doctor blade was appropriately adjusted on one side of an aluminum foil having a thickness of 20 µm so that the mass of the positive electrode mixture after drying was 17 mg / cm 2, and the positive electrode paste was applied.

As a result, the elongation of the positive electrode paste was poor, and the coating workability defect "is" was regarded as the exposure (cutting) of the aluminum foil visible on the coating surface except for the end portion. The results of the coating workability test are shown in Tables 7 to 10 together.

[Measurement of Drying Time of Positive Electrode Paste]

Among the positive electrodes immediately after the coating, the positive electrodes according to some examples and comparative examples were measured for mass before drying and for each fixed time after loading on a hot plate at 60 ° C. The time point when no mass change was seen was regarded as the end of drying, and was referred to as drying time. Table 11 shows the measurement results of the drying time.

[Measurement of Peel Strength of Positive Electrode]

Using the positive electrode after the cutting, a mending tape (manufactured by Scotch, product number: MP-18S) was applied to the surface of the positive electrode mixture layer, and about 2.3 cm / s so that the angle between the surface of the tape and the positive electrode was 180 °. Tensile was stretched at a speed and the stress at that time was measured using a push pull gauge (DIGITAL FORCE GAUGE DPS-2, manufactured by IMADA). The average value of the measured value was computed except the part where the value of peeling start and peeling end is unstable, and it was called peeling strength. The measurement results of the peel strength are shown in Tables 7 to 10.

[Test Results and Discussion]

[Faste Solids, Drying Speed and Drying Time]

From Example 4 and Comparative Examples 1 and 2, it can be seen that the positive electrode paste having a high solid content has a short drying time after application, regardless of the presence or absence of a copolymer.

For this reason, it turns out that the time required for drying can be shortened by lowering the content rate of NMP in paste, ie, raising solid content of a positive electrode paste.

Paste Solid Content and Paste Viscosity

As can be seen by comparing Comparative Examples 1 and 2, it can be seen that when the paste solid content is made high, breakage occurs during coating. This breakage of the positive electrode can be explained by the lack of fluidity of the paste, that is, the high viscosity.

The positive electrode paste of Example 4 has a high paste solid content in the same manner as in Comparative Example 2, but by adding Copolymer A, the paste viscosity can be lowered to the same as in Comparative Example 1, whereby the breakage during application of the positive electrode is eliminated. It can be seen that it can be solved.

[Confirmation of Paste Viscosity Reduction Effect]

In Examples 4 and 7 to 10 and Comparative Examples 2 to 6 corresponding to each, even when various positive electrode active materials and conductive agents were used, the effect of reducing the paste viscosity by copolymer A can be confirmed. Since the absolute value of paste viscosity changes with the kind of positive electrode material and paste solid content, in order to confirm the effect of addition of copolymer A, it is reasonable to compare the viscosity reduction rate instead of the absolute value of viscosity. From the result of a viscosity reduction rate, the paste viscosity reduction effect by addition of copolymer A is confirmed also in any paste. The viscosity reduction rate of the battery positive electrode paste which concerns on this invention is larger than zero.

[Added Copolymer]

1 plots the positive electrode paste viscosity for Examples 1 to 6 and Comparative Example 2. FIG. As can be seen from FIG. 1, it can be seen that the viscosity of the paste decreases as the amount of the copolymer added increases. However, since the viscosity reduction effect suitable for the addition amount is hard to be acquired, so that the addition amount of a copolymer increases, 1-16% of the addition amount of a copolymer is preferable at the mass ratio of a electrically conductive agent.

[Mass Ratio of Structural Unit (a) and Structural Unit (b)]

From Examples 35 to 37 and Reference Example 3, it can be seen that when the mass ratio (a) / (b) of the structural unit (a) and the structural unit (b) is a large value, a copolymer that is difficult to obtain a paste reduction effect exists. have. This is considered to be due to the small effect of suppressing the aggregation of particles in the paste due to the strong steric repulsion between the particles caused by the structural unit (b) because the proportion of the structural unit (b) is too small in the copolymer. . For this reason, the mass ratio (a) / (b) of a structural unit (a) and a structural unit (b) may be not too large.

Moreover, even if it is a copolymer which is hard to acquire a paste reduction effect, a paste reduction effect is exhibited by increasing content of the copolymer in a paste.

[Type of binder]

The Example and comparative example shown in Table 4 are a result of changing the binder in paste into PVDF of a higher molecular weight type. Since the positive electrode mixture peeling strength can be improved by high molecular weight binder, it is preferable. It is especially preferable when a positive electrode is produced using a bulky positive electrode active material, a finely divided positive electrode active material, a carbon-coated positive electrode active material, and the like.

Also in the case of changing the kind of binder in Table 4, the effect of paste viscosity reduction by addition of a copolymer is confirmed.

In addition, from the comparison between Example 3 and Example 50 and the comparison between Example 24 and Example 51, it can be seen that, as the binder in the paste, a lower molecular weight type can obtain a better paste viscosity reducing effect. Therefore, as long as the problem does not arise in the positive electrode mixture peeling strength, the binder in the paste has a lower molecular weight type.

In addition, it can be seen from Comparative Examples 7 and 8 that there is a copolymer in which a paste viscosity reducing effect is not obtained.

From these, it turns out that the structure of a copolymer is very important for the effect of reducing paste viscosity and ensuring peeling strength of a positive electrode mixture. The detail is considered as follows.

Since the comparative examples 7, 8 are copolymers which do not contain a structural unit (a), it is thought that the adsorption action | action to a positive electrode active material or a conductive agent is not enough. At the same time, it is considered that the unadsorbed copolymer is adsorbed onto the PVDF and the adhesion between the positive electrode mixture and the aluminum foil is lowered.

In addition, although not shown here, the present inventors confirmed that the paste viscosity reduction effect was not expressed even when the copolymer used for the comparative examples 7, 8 was added in large quantities.

As described above, according to the present invention, it is possible to provide a battery positive electrode paste having a high solid content which can shorten the drying time of the positive electrode mixture without impairing the coating property of the positive electrode paste or the adhesion of the positive electrode mixture after coating. It is possible.

Although this invention was demonstrated in detail with reference to the specific aspect, it is clear for those skilled in the art for various changes and correction to be possible, without leaving | separating the mind and range of this invention.

In addition, this application is based on the JP Patent application (2012-085003) of an application on April 3, 2012, The whole is taken in into consideration. In addition, all references cited herein are incorporated as a whole.

Claims (18)

A battery positive electrode paste comprising a copolymer as a positive electrode active material, a conductive agent, a solvent, a binder, and a dispersant, wherein the copolymer is represented by a structural unit (a) represented by the following general formula (1) and the following general formula (2) It is a copolymer containing the structural unit (b) used, The mass ratio (structural unit (a) / structural unit (b)) of a structural unit (a) and a structural unit (b) is 0.1-5.4, and content of the said copolymer is The battery positive electrode paste which is 30 mass parts or less with respect to 100 mass parts of said electrically conductive agents.

(In formula, R ¹ , R ² , R ³ , R ⁵ , R ⁶ , R ⁷ and R ⁹ are the same or different and represent a hydrogen atom, a methyl group or an ethyl group, and R ⁴ represents a hydrocarbon group having 12 to 22 carbon atoms. , R ⁸ represents a straight or branched alkylene group of 2 to 4 carbon atoms, X ¹ , X ² represents an oxygen atom or NH, p represents a number of 1 to 50) The method of claim 1,
The battery positive electrode paste whose weight average molecular weights of the said copolymer are 9,000-100 million. The method according to claim 1 or 2,
A battery positive electrode paste, wherein the binder is any one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, and polyacrylonitrile. The method according to claim 1 or 2,
The battery positive electrode paste whose total of content of a structural unit (a) and a structural unit (b) is 40 mass% or more in the said copolymer. The method according to claim 1 or 2,
The battery positive electrode paste whose content of the said copolymer is 0.5-25 mass parts with respect to 100 mass parts of said electrically conductive agents. The method according to claim 1 or 2,
The battery positive electrode paste whose content of a structural unit (a) is 5 mass% or more and 90 mass% or less in the said copolymer. The method according to claim 1 or 2,
The battery positive electrode paste whose content of a structural unit (b) is 10 mass% or more and 85 mass% or less in the said copolymer. The method according to claim 1 or 2,
A battery positive electrode paste, wherein the solvent is any one of N-methyl-2-pyrrolidone, dimethylformamide, dimethyl sulfoxide or water. The method according to claim 1 or 2,
The battery positive electrode paste whose p of the said General formula (2) is 1 or more and 35 or less. The method according to claim 1 or 2,
The battery positive electrode paste whose X <^1> of the said General formula (1) is an oxygen atom. The method according to claim 1 or 2,
The battery positive electrode paste whose R <^3> of the said General formula (1) is a hydrogen atom or a methyl group. The method according to claim 1 or 2,
The battery positive electrode paste whose R <^1> and R <^2> of the said General formula (1) is a hydrogen atom. The method according to claim 1 or 2,
The battery positive electrode paste whose X <^2> of the said General formula (2) is an oxygen atom. The method according to claim 1 or 2,
The battery positive electrode paste whose R <^7> of the said General formula (2) is a hydrogen atom or a methyl group. The method according to claim 1 or 2,
The battery positive electrode paste whose R <^5> and R <^6> of the said General formula (2) is a hydrogen atom. The method according to claim 1 or 2,
The battery positive electrode paste whose R <^8> of the said General formula (2) is an ethylene group or a propylene group. The method according to claim 1 or 2,
The battery positive electrode paste whose viscosity reduction rate of the said battery positive electrode paste is larger than zero. The method according to claim 1 or 2,
The battery positive electrode paste whose content of the said copolymer in the said battery positive electrode paste is 0.02 mass% or more and 1 mass% or less.

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