JPH08250124A - Battery electrode - Google Patents

Abstract

PURPOSE: To provide an electrode for forming a battery excellent in a cycle property, a preservation characteristic, and safety, by binding an electrode active material, composed of a carbonaceous material, and a crosslinking polymer particle by an organic binder. CONSTITUTION: In a battery electrode wherein a carbonaceous material is adopted as electrode active material, the electrode active material and a crosslinking polymer particle are bound by an organic binder (polyvinyl alcohol, etc.,) to manufacture a battery electrode. The crosslinking polymer particle is a crosslinking particle wherein a crosslinking property polyvinyl monomer of about 2wt.% or more is used to be polymerized, divinyl benzene, etc., is used for crosslinking property monomer, and the particle diameter of a crosslinking particle and the mean particle diameter of the carbonaceous material are made about 0.03-5μm and about 0.1-50μm respectively. In addition, the crosslinking particle is used about 1-100 wt. parts to the carbonaceous material of 100 wt. parts. A battery, having excellent electric current efficiency, low overvoltage, small size, light weight, and excellent performance, can be obtained by using this electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has a cycle property, a storage property,
The present invention relates to an electrode for forming a battery having excellent safety. In particular, the present invention relates to an electrode suitable for a new secondary battery.

[0002]

2. Description of the Related Art In recent years, electronic devices have been remarkably reduced in size and weight, and accordingly, there has been a great demand for reduction in size and weight of batteries as power sources. Non-aqueous batteries have been attracting attention because it is impossible to meet the above requirements with conventional batteries using general aqueous electrolytes. Such non-aqueous batteries have excellent performance in terms of size and weight reduction, and primary batteries typified by lithium batteries and further lithium / titanium disulfide secondary batteries have been proposed, some of which have been proposed. Has already been put to practical use.

However, although such a non-aqueous battery is excellent in terms of performance such as high energy density and small size and light weight, it has this drawback in the field of secondary battery which is required to have output characteristics as compared with a water battery represented by a lead battery. This is one of the factors that hinder practical application. The reason why the non-aqueous battery is inferior in the output characteristics is that the ionic conductivity is high in the case of the aqueous electrolytic solution and usually has a value of the order of 10 ⁻¹ Ω ⁻¹ CM ⁻¹ , whereas that of the non-aqueous battery is 10 ⁻² to 10 ^{−. This} is because it has a low ionic conductivity of ⁴ Ω ^-1 CM ^-1 .

As one method for solving such a problem, it is conceivable to increase the electrode area, that is, to use a thin film or a large area electrode.

As a conventional method for forming an electrode, a method in which an electrode active material and an organic polymer are mixed and compression-molded is generally used. In the case of such a method, there is an advantage that the binder, which is an insulating material, has relatively little influence on the electrode active material, and the type and shape of the binder used are also limited, but on the other hand, it is not possible to manufacture a thin film / large area electrode. It's extremely difficult.

On the other hand, as a method for producing a thin film / large area electrode, after dispersing an electrode active material in a solvent solution of an organic polymer,
A method of forming an electrode by coating and drying is known. According to this method, a thin film and a large area electrode can be easily obtained, but on the other hand, the influence of the binder, which is an insulating material, on the electrode active material is significantly large, and when the electrode is assembled into a battery, for example, it is remarkable. This was not a practical method because the overvoltage increased.

As an aqueous binder, a water-soluble polymer such as carboxymethyl cellulose, polyvinyl alcohol, polyacrylic acid salt, starch or a styrene / butadiene latex having a high butadiene content and a high gel content is known (Japanese Patent Laid-Open Publication No. Hei 10 (1999) -242242). 5-7446
1). However, the water-soluble polymer is inferior in binder performance because it uniformly adheres to the surface of the electrode active material, and styrene / butadiene latex having a high gel content is not sufficient in binder performance, and therefore a large amount of binder must be used. However, there was a problem in the performance of the battery.
Thus, it was difficult to form an electrode for a high-performance battery, especially a secondary battery, only by binding the active material with the organic binder.

[0008]

On the basis of the above situation,
The present invention provides an electrode having excellent battery characteristics in a battery using a carbonaceous material as an electrode active material, mainly in a secondary battery.

[0009]

[Means for Solving the Problems] The present inventors diligently studied various water-based polymer latices, and by binding cross-linked polymer particles together with an electrode active material with an organic binder, the properties are high and particularly the cycle property is improved. The present invention has been achieved by finding that an excellent electrode can be obtained.

That is, the present invention is a battery electrode using a carbonaceous material as an electrode active material, wherein the electrode active material and the crosslinked polymer particles are bound by an organic binder. .

The present invention will be described in detail below.

The crosslinked polymer particles in the present invention are crosslinked particles obtained by using 2% by weight or more, preferably 5% by weight or more, of a crosslinkable polyvinyl monomer (hereinafter referred to as a crosslinkable monomer). The polymerization method is not particularly limited, and the polymerization can be performed by emulsion polymerization, suspension polymerization, dispersion polymerization, microdispersion polymerization, or the like. An example of a preferable synthesis method is JP-A-1-315454. As the crosslinkable monomer, a polysubstituted vinyl aromatic compound typified by divinylbenzene, or a copolymer of two or more polyvalent acrylates or polyvalent methacrylates typified by ethylene glycol dimethacrylate or trimethylolpropane triacrylate. It is a compound having a double bond.
Here, butadiene is not included in the crosslinkable monomer. The monomer other than the crosslinkable monomer may be any monomer that can be copolymerized therewith, and specifically, styrene, α-methylstyrene, butadiene, methyl (meth) acrylate, butyl (meth) acrylate, (meth) acrylonitrile, hydroxy. Examples thereof include ethyl (meth) acrylate, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and (meth) acrylamide.

In the present invention, the crosslinkable polymer particles enter the space between the electrode active materials in the formation of the battery electrode and act as a spacer for preventing the aggregation of the active material, and it is speculated that this makes the electrode excellent in cycle performance. To be done. Further, in the porous polymer particles or hollow polymer particles according to the second embodiment of the present invention, by further containing an electrolyte solution component in the pores inside the crosslinked particles to improve the output characteristics of the battery electrode. Conceivable.

The particle size of the crosslinked particles in the present invention is 0.03.
It is preferable that it is smaller than ⅓ of the average particle diameter of the electrode active material used in the range of μm or more, specifically, 0.03 to 5 μm.
m, and more preferably 0.1 to 2 μm. Further, the shape of the crosslinked particles is preferably spherical, but amorphous particles obtained by crushing or crushing a resin can also be used.

The crosslinked particles in the present invention are more preferably porous particles or hollow particles. The method for producing the porous particles is not particularly limited, but for example, it can be obtained by suspension polymerization or microdispersion polymerization of a mixture of a monomer containing a crosslinkable monomer and an organic solvent. The pore size of the porous particles is preferably 0.01 to 0.1 μm. The method for producing the hollow particles is not particularly limited,
For example, Japanese Patent Publication No. 4-68324 or Japanese Patent Application Laid-Open No. 63-
It can be synthesized by the method described in 135409. The hollow particles preferably have an inner hole / outer hole ratio of 0.1 to 0.7. When the crosslinked particles in the present invention are more porous particles or hollow particles, not only a battery electrode having excellent cycleability but also a battery electrode having further excellent output characteristics can be obtained.

In the present invention, carbon material 1 which is an electrode active material
The amount of crosslinked particles is 1 to 100 parts by weight, preferably 3 to 70 parts by weight, and more preferably 5 to 50 parts by weight, based on 00 parts by weight. If the amount is more than 100 parts by weight, the amount of the active material is relatively decreased and the battery performance is deteriorated. Further, if it is less than 1 part by weight, no substantial effect can be seen.

In the present invention, an organic binder is used as a binder in order to bind a carbon material as an electrode active material and crosslinked particles to form an electrode component. As the organic binder, an aqueous dispersion of polymer particles typified by styrene / butadiene latex, an aqueous solution of a water-soluble polymer such as polyvinyl alcohol, carboxymethyl cellulose, or methyl cellulose or a low molecular weight substance, and further styrene butadiene rubber, nitrile rubber, fluororubber An organic solvent solution of a polymer such as silicone rubber or a low molecular weight substance can be used.

The average particle size of the carbonaceous material used in the present invention is 0.1 to 50 μm in terms of current efficiency and viscosity of the coating mixture.
Furthermore, 1-20 micrometers is preferable. If necessary, the carbonaceous material, the crosslinked particles and the organic binder are further mixed and kneaded with water, a solvent, a dispersant, a pH adjuster and a stabilizer, and then applied and coated on a substrate to form an electrode. Form. At this time, if necessary, it may be molded together with the current collector material, or alternatively, a current collector such as an aluminum foil or a copper foil may be used as the base material.

As the coating method, an arbitrary coater head such as a reverse roll method, a comma bar method, a gravure method or an air knife method can be used.

The battery electrode of the present invention can be used in both aqueous and non-aqueous batteries, but when used as the negative electrode of a non-aqueous battery, particularly excellent battery performance can be obtained.

In the case of assembling a non-aqueous battery using the secondary battery electrode of the present invention, the electrolyte of the non-aqueous electrolyte is not particularly limited, but as an example, LiClO ₄ , LiB
F ₄ , LiAsF ₆ , CF ₃ SO ₃ Li, LiPF ₆ , Li
I, LiAlCl ₄ , NaClO ₄ , NaBF ₄ , Na
I, (n-Bu) ₄ NClO ₄ , (n-Bu) ₄ NBF ₄ ,
Examples include KPF _{6 and the} like. Examples of the organic solvent of the electrolytic solution used include ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds,
Chlorinated hydrocarbons, esters, carbonates, nitro compounds, phosphoric acid ester compounds, sulfolane compounds and the like can be used. Among them, ethers, ketones, nitriles, chlorinated hydrocarbons , Carbonates, and sulfolane compounds are preferable.

Typical examples of these are tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, anisole, monoglyme, acetonitrile, propionitrile, 4-methyl-2-pentanone, butyronitrile, valeronitrile, benzonitrile, 1 , 2-
Examples thereof include dichloroethane, γ-butyrolactone, dimethoxyethane, methyl formate, propylene carbonate, ethylene carbonate, dimethylformamide, sulfolane, 3-methyl-sulfolane, trimethyl phosphate, triethyl phosphate, and mixed solvents thereof. However, it is not necessarily limited to these.

The positive electrode material to be used is not particularly limited, but for example, MnO ₂ , MoO ₃ , V
₂ O ₅ , V ₆ O ₁₃ , Fe ₂ O ₃ , Fe ₃ O ₄ , Li _(1-X) CoO
_{2, Li (1-X)} NiO 2, Li x Co y Sn z O 2, TiS 2,
_{TiS 3, MoS 3, FeS 2} , CuF 2, NiF inorganic compounds such as _2, carbon fluoride, graphite, vapor-grown carbon fiber and / or its pulverized product, PAN-based carbon fibers and /
Alternatively, pulverized products thereof, carbon materials such as pitch-based carbon fibers and / or pulverized products thereof, and conductive polymers such as polyacetylene and poly-p-phenylene.

In particular, Li _(1-X) CoO ₂ , Li _(1-X) Ni
O ₂ , Li _x Co _y Sn _z O ₂ , Li _(1-X) Co _(1-Y) Ni _y O
_When a lithium ion-containing composite oxide such as ₂ is used, both the positive and negative electrodes can be assembled in a discharged state, which is a preferable combination.

Further, if necessary, a separator, a current collector,
A battery is constructed using parts such as terminals and insulating plates. Further, the structure of the battery is not particularly limited, but a positive electrode, a negative electrode, if necessary, a paper-type battery having a separator in a single layer or a multilayer, or a positive electrode, a negative electrode, if necessary, a separator roll. An example is a form of a cylindrical battery that is wound into a shape.

[0026]

The present invention will be described in more detail with reference to the following examples.

Synthesis of Crosslinked Polymer Particles In the monomer composition shown in Table 1, other conditions are described in JP-A-1-315.
Crosslinked particles 1 to 5 were obtained in the same manner as in Example 1 of 454. The crosslinked particles 1 are non-crosslinked polymer particles.
Further, the crosslinked particles 5 are n-hexane 30 together with the monomer.
Then, the mixture was synthesized by adding parts to obtain porous particles having a pore size of 0.05 μm and a specific surface area of 15 m ² / g. Similarly, No in Table 1
In the monomer composition of 6, other conditions are Japanese Patent Publication No.
Crosslinked particles 6 were obtained in the same manner as in Example 1 of 4. The crosslinked particles 6 were single-hole hollow particles having an outer diameter of 0.45 μm and an inner hole diameter of 0.28 μm.

[0028]

[Table 1]

Electrode formation 100 parts by weight of needle coke crushed product (average particle size 12 μm) and 10 parts by weight of crosslinked particles (1) to (6), styrene / butadiene latex (made by Japan Synthetic Rubber Co., Ltd.) as an organic binder. # 0545) as a solid content, 6 parts by weight of a carboxymethyl cellulose aqueous solution as a thickener, 1 part by weight of a solid content, and 1 part by weight of 0.1N ammonia water were added, and mixed and defoamed to obtain an electrode coating liquid. . Using a 10 μm nickel foil as a base material, this coating solution was applied with a roll coater at 150 g /
m ² was applied and dried to obtain a negative electrode having a thickness of 145 μm. On the other hand, Li _1.03 Co _0.95 Sn _{0.042 having an} average particle size of 2 μm
100 parts by weight of O _2, 7.5 parts by weight of graphite powder, and 2.5 parts by weight of acetylene black are mixed, 50 parts by weight of a methyl isobutyl ketone solution of fluororubber (concentration 4% by weight) is added, and the mixture is stirred to form a coating liquid. did. Commercially available Al foil (thickness 1
5 μm) as a base material and this coating solution was applied and dried at 290 g / m ² to obtain a positive electrode having a thickness of 110 μm.

The negative electrode and the positive electrode are 0.9 × 5.5 cm
It was cut out and assembled into a lithium secondary battery. These are designated as Comparative Example 1 and Examples 1 to 5, respectively. Comparative Example 2
Is a battery assembled with electrodes formed without cross-linked particles. Charge this battery to 4.2V, 10mA
The cycle of discharging until 2.5 V was repeated. Table 2 shows the overvoltage, current efficiency, capacity retention rate in charge / discharge cycle, and capacity change under accelerated storage conditions of these batteries.

[0031]

[Table 2]

[0032]

EFFECT OF THE INVENTION The battery using the electrode of the present invention has excellent current efficiency, excellent capacity retention (cycle property), low overvoltage, and excellent high temperature retention performance. It is extremely useful for obtaining excellent batteries of.

Claims (2)

[Claims] 1. A battery electrode using a carbonaceous material as an electrode active material, wherein the electrode active material and crosslinked polymer particles are bound by an organic binder. 2. The battery electrode according to claim 1, wherein the crosslinked polymer particles are porous polymer particles or hollow polymer particles.