JPH09115504A - Electrode for battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a battery on which dispersion of application weight is reduced by setting respective ones of an organic solvent quantity of an active material layer to form a battery electrode by covering an electric conductor surface, the moisture content, dospersion of application weight and a necessary rate of application density in a specific value. SOLUTION: An electric conductor surface is covered with an active material layer containing a conductive inorganic substance and a binder, and a battery electrode is formed. The content of an organic solvent in this active material layer is not more than 200ppm, and the moisture content is not more than 100ppm. When dispersion of application weight to satisfy a specific condition based on active material weight per cm<2> and average application weight is set not more than 4% and a rate of application density being density of the active material layer covering an electric conductor to average true density totaled by multiplying true density of respective materials to form the active material layer by a weight percent of the respective materials is set in 45 to 95%, an electrode for a battery on which dispersion of application weight is reduced is formed. Therefore, when this electrode is used, a high characteristic battery on which turbulence of a capacity balance between a positive electrode and a negative electrode is not caused can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery electrode and a method for manufacturing the same, and more particularly, to a battery electrode suitable for a secondary battery electrode and a method for easily manufacturing the battery electrode.

[0002]

2. Description of the Related Art Recently, as a large battery for electric vehicles,
Attention has been paid to lithium ion secondary batteries having excellent characteristics such as high energy density and high charge / discharge density.

Usually, this lithium ion secondary battery has an electrode and an electrolytic solution. Specific examples of the substance used for the electrode and the electrolytic solution are as follows.

[0004] Materials used for the positive electrode include lithium-containing composite oxides such as lithium cobalt oxide (LiC).
oO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickel oxide (LiNiO ₂ ) and the like.

Examples of the substance used for the negative electrode include carbon materials such as natural graphite, artificial graphite, non-graphitizable carbon (graphitic carbon), mesocarbon microbeads, pitch-based carbon fiber and vapor grown carbon fiber. .

Examples of the substance used in the electrolytic solution include a non-aqueous electrolytic solution in which a lithium salt and an organic solvent are mixed. Examples of the lithium salt include LiClO ₄ , LiPF ₆ , Li
BF _4, LiAsF _6, such as LiCF ₃ SO ₃ and the like. As the organic solvent, propylene carbonate,
Examples thereof include ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and mixtures thereof.

The lithium ion secondary battery composed of the above-mentioned substances is characterized by high energy density, excellent cycle characteristics, and high safety as compared with other batteries.

The electrodes of the above lithium ion secondary battery are generally manufactured as follows. That is, a solution obtained by dissolving a binder in an organic solvent is mixed with the above-mentioned lithium-containing oxide or carbon material to obtain a mixture, and this mixture is applied to a conductor sheet, for example, a metal sheet, and heated. It is produced by removing the organic solvent by drying.

However, in the above lithium ion secondary battery, the presence of impurities such as water causes a problem that the cycle life is significantly reduced. That is, if the electrode is not sufficiently dried in the manufacturing process, water and an organic solvent remain, which causes deterioration of the cycle characteristics of the battery.

When the electrode is heated and dried at a high temperature in order to remove these impurities, the conductor sheet is oxidized, the conductivity of the conductor is significantly lowered, and the internal resistance of the battery is increased. However, it may be a factor that shortens the cycle life of the battery or adversely affects the battery characteristics at high current density.

On the other hand, in this lithium ion secondary battery, especially a cylindrical battery, the positive electrode and the negative electrode are generally wound in a roll shape with a separator interposed therebetween. It is preferable that the capacities per unit area are equal. Here, the capacity per unit area is the capacity per unit weight of the positive electrode constituent material or the negative electrode constituent material obtained by a three-electrode type cell or a coin type cell in which the counter electrode is metallic lithium, and it is applied to the conductor. It is obtained from the weight of the electrode active material layer per unit area thus obtained. If the capacities per unit area of the facing positive electrode and the negative electrode are not equal, lithium deposits on the surface of the negative electrode, causing an explosion, and problems such as insufficient battery capacity.

There is a problem that unevenness in the coating weight and thickness of the electrode finds out the capacity balance between the positive electrode and the negative electrode, causes various problems such as the precipitation of lithium, and greatly affects the battery characteristics.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery electrode having a small variation in coating weight and a method for manufacturing the same.

An object of the present invention is to provide a method of manufacturing a battery electrode which has a small amount of residual water and a small amount of residual solvent and which can manufacture a battery electrode without oxidizing a conductor.

[0015]

The invention according to claim 1 for solving the above-mentioned problems is characterized in that the surface of a conductor is coated with an active material layer containing a conductive inorganic substance and a binder. The content of the organic solvent in the active material layer is at most 200.
ppm, the water content in the active material layer is at most 100 ppm, the coating weight variation of the active material layer defined below is at most 4%, and the active material layer The ratio (unit:%) of the coating density defined below to the average true density defined in (4) is 45 to 95%.
Coating weight: weight of active material layer per square centimeter covering conductors variation in coating weight: [(average coating weight-coating weight) / average coating weight] x 100 Average true density: The true density of each material forming the active material layer is multiplied by the weight fraction of each material in the active material layer, and the sum is calculated. True density: Density of material itself Coating density: Covering conductor The density of the formed active material layer is the battery electrode according to claim 1, wherein the conductive inorganic material is a carbon material, and the invention according to claim 3 is The conductive inorganic substance is a battery electrode according to claim 1, wherein the conductive inorganic substance is a carbon material, and the active material layer is the carbon material. Further contains a lithium-containing oxide The battery electrode according to claim 1, wherein the invention comprises a binder, a conductive inorganic substance, and an organic solvent, and has a viscosity of 20 to 70 dPa.
A dispersion liquid adjusted to s is prepared, the dispersion liquid is applied to a conductor, and the dispersion liquid applied to the conductor is dried to obtain an active material layer-coated conductor. A method for producing an electrode for a battery, wherein the body is pressure-molded, and the invention according to claim 6 is characterized in that the dispersion liquid applied to the electric conductor contains oxygen having an oxygen concentration of at most 100 ppm. The method for manufacturing a battery electrode according to claim 5, wherein the battery electrode is dried in an atmosphere.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The battery electrode of the present invention and the method for producing the same will be described in detail below.

<Battery Electrode> The battery electrode of the present invention is
The surface of the conductor is coated with an active material layer obtained by dispersing a conductive inorganic substance in a binder.

The conductor is preferably a material having a function as a support for a battery electrode, chemical resistance, electrochemical stability and conductivity, and is usually formed of a metal such as copper, aluminum or iron. It Preferred metals for the conductor are copper and aluminum.

The form of the conductor is appropriately determined according to the form of the secondary battery, but is usually a thin sheet.

The active material layer coating the surface of the conductor is
A conductive inorganic substance is dispersed in a binder.

The conductive inorganic substance may be a conductive inorganic substance or a mixture of a conductive inorganic substance and a non-conductive inorganic substance. For example, a carbon material and a mixture thereof are preferable examples. Can be mentioned.

Here, the carbon material means a material which is substantially made of carbon. Examples of this carbon material include natural graphite, artificial graphite, non-graphitizable carbon, mesocarbon microbeads, PAN-based carbon fiber, cellulose-based carbon fiber, pitch-based carbon fiber, vapor-grown carbon fiber, and dehydrated PVA.
Examples include carbon-based fibers, lignin carbon fibers, glassy carbon fibers, activated carbon fibers, and the like. These can be used alone or in combination of two or more.

Examples of the binder for forming the active material layer include fluorinated resins such as polyvinylidene fluoride and polytetrafluoroethylene, polyolefins such as polyethylene and polypropylene, and copolymers thereof.

In the present invention, when the battery electrode is used as the negative electrode, the active material layer is used as the binder in the conductive inorganic material, particularly the carbon material, and further the vapor grown carbon fiber, preferably the graphitized vapor phase. Made of grown carbon fiber.

The vapor grown carbon fiber can be manufactured by a vapor growth method.

As a method for producing a vapor grown carbon fiber by the vapor growth method, there are a so-called substrate growth method and a fluidized vapor phase method.

In the substrate growth method, a catalyst metal such as a transition metal or a transition metal compound is supported on the substrate and a carbon source gas such as a hydrocarbon gas is circulated on the substrate while being heated to a high temperature, so that the surface of the substrate is covered. It is a method of producing carbon fibers, the fluidized vapor phase method does not use a substrate,
By vaporizing a metal compound capable of providing a catalytic metal source, such as a catalytic metal, and a carbon source, such as a carbon compound, such as a hydrocarbon, and flowing the same in a high-temperature reaction tube,
This is a method of generating carbon fibers in a space. The carbon source and the catalyst metal source may be the same compound, and examples of such a compound include metallocene such as ferrocene.

Specifically, Japanese Patent Laid-Open No. 52-107320
JP-A-57-117622, JP-A-58-156
No. 512, JP-A-58-180615 and JP-A-60-180
185818, JP-A-60-224815, JP-A-60-231821, JP-A-61-132630,
JP-A-61-13600, JP-A-61-13266
No. 3, JP-A-61-225319, JP-A-61-22
No. 5322, JP-A-61-225325, JP-A-61-225325
JP-A-225327, JP-A-61-225328, JP-A-61-2275425, JP-A-61-282427
And the vapor-grown carbon fibers produced by the methods described in JP-A-5-222609.

In the present invention, vapor-grown carbon fibers should be understood as a broad concept including graphitized vapor-grown carbon fibers. In the present invention, both graphitized vapor-grown carbon fiber and non-graphitized vapor-grown carbon fiber are suitable, but rather, graphitized vapor-grown carbon fiber is more preferable.

The vapor-grown carbon fiber before graphitization (hereinafter sometimes referred to as non-graphitized vapor-grown carbon fiber) usually has a specific surface area of at most 5 m ² / g.
, Preferably at most 3 m ² / g, more preferably at most 2 m ² / g. This non-graphitized vapor-grown carbon fiber has a specific surface area of at most 5 m ² /
When it is g, the object of the present invention can be achieved even better, the charge and discharge efficiency is high, and the cycle life is long. The specific surface area can be measured by a BET method.

The non-graphitized vapor grown carbon fiber is usually
Its average aspect ratio is 2 to 30, preferably 3
-20, more preferably 5-15. When the average aspect ratio of the non-graphitized vapor grown carbon fiber is 2 to 30, the object of the present invention can be better achieved.

The average aspect ratio of the non-graphitized vapor-grown carbon fiber was determined by taking a scanning electron micrograph of the non-graphitized vapor-grown carbon fiber and observing the scanning electron micrograph. 1,000 samples were randomly selected from the non-graphitized vapor-grown carbon fibers shown in Fig. 3, and the selected non-graphitized vapor-grown carbon fibers were assumed to be cylindrical bodies. It is determined by measuring the length and diameter of the grown carbon fiber, taking the length and diameter as the aspect ratio of each non-graphitized vapor grown carbon fiber, and averaging the aspect ratios of 1,000 samples.

The specific surface area is at most 5 m ² / g,
Suitable non-graphitized vapor-grown carbon fibers having an average aspect ratio of 2 to 30 have a carbon interplane distance of at most 0.1 mm.
338 nm, and even if the thickness of the carbon crystallite is small, it is 40
It can be obtained by cutting non-graphitized vapor grown carbon fiber having a diameter of 1 nm and a diameter of 1 to 10 μm by an appropriate cutting means. As the cutting means, a normal crushing means such as a ball mill, a roller mill, and a jet mill can be adopted, but the fibers are pressurized and compressed with a hybridizer or a high compressive force capable of breaking the fibers with a high impact force. Means are particularly preferred.

The non-graphitized vapor grown carbon fiber preferably used has an average diameter of usually 1 to 10 μm, preferably 2 to 5 μm. When the average diameter of the non-graphitized vapor-grown carbon fiber is within the range of 1 to 10 μm, the non-graphitized vapor-grown carbon fiber can be easily dispersed and the fibers can be easily contacted with each other.

On the other hand, as for the graphitized vapor grown carbon fiber, the non-vapor grown carbon fiber is 2,000 ° C. or higher, preferably 2,
It can be produced by heat treatment in the range of 000 ° C to 3,000 ° C.

An inert gas atmosphere is usually adopted as the atmosphere for the heat treatment. The heat treatment time is usually 5 minutes or more.

The specific surface area of the graphitized vapor grown carbon fiber is usually at most 5 m ² / g, preferably at most 3 m ² / g, more preferably at most 2 m ² / g. . When the specific surface area of the graphitized vapor grown carbon fiber is at most 5 m ² / g, the object of the present invention can be better achieved, the charge and discharge efficiency is high, and the cycle life is long. The method for measuring the specific surface area is as described above.

The graphitized vapor grown carbon fiber usually has an average aspect ratio of 2 to 30, preferably 3 to.
20, more preferably 5 to 15. When the average aspect ratio of the graphitized vapor grown carbon fiber is 2 to 30, the object of the present invention can be better achieved.

The method for measuring the average aspect ratio of the graphitized vapor grown carbon fiber is as described above.

The specific surface area is at most 5 m ² / g,
A suitable graphitized vapor grown carbon fiber having an average aspect ratio of 2 to 30 has a carbon network plane distance of at most 0.3.
38 nm, 40 n even if the thickness of the carbon crystallite is small
m by cutting a graphitized vapor grown carbon fiber having a diameter of 1 to 10 μm by an appropriate cutting means,
Obtainable. As the cutting means, a ball mill,
A usual crushing means such as a roller mill or a jet mill can be adopted, but a hybridizer capable of breaking the fiber with a high impact force or a means for pressurizing and compressing the fiber with a high compression force is particularly preferable.

The graphitized vapor grown carbon fiber usually has an average diameter in the range of 1 to 10 μm, preferably 2 to 5 μm.
Within the range. When the average diameter of the graphitized vapor grown carbon fiber is in the range of 1 to 10 μm, the graphitized vapor grown carbon fiber can be easily dispersed and the fibers can be easily contacted with each other.

The graphitized vapor-grown carbon fiber which is preferably used has a highly developed graphite structure, and in terms of the degree of development of the condensed cyclic carbon network plane, the carbon network plane distance (d _oo2 ) is Usually, it is at most 0.338 nm or less, preferably at most 0.337 nm, more preferably at most 0.3355 to 0.3365 nm.

The carbon network plane distance can be measured by the Gakushin method, which is obtained from X-ray diffraction as described in "Carbon Technology I", Science and Technology Publishing, 1970, p. 55.

The graphitized vapor-grown carbon fiber which is preferably used is such that the thickness of the condensed cyclic carbon network planes, that is, the carbon crystallite thickness (L _c ) is usually at least 40 n.
m, preferably at least 60 nm, more preferably at least 80 nm.

The thickness of this carbon crystallite is "Carbon Technology I".
X described on page 55 of Science and Technology Publishing Co., Ltd., published in 1970.
It can be measured by the Gakushin method obtained from line diffraction.

The graphitized vapor grown carbon fiber preferably used has a preferable spin density of at most 8 × 10 ¹⁸ spins / s, more preferably at most 7 × 10 ¹⁸ spins, as measured by electron spin resonance absorption method. / s.

This spin density can be measured by electron spin resonance.

When the battery electrode of the present invention is used as a positive electrode, the active material layer comprises the binder, the conductive inorganic material, especially the carbon material and the lithium-containing oxide.

As the lithium-containing oxide, lithium cobalt oxide (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickel oxide (LiNiO ₂ ).
₂ ) and so on.

When the battery electrode is the negative electrode, the content of the conductive inorganic substance in the active material layer is usually 85 to 97% by weight, preferably 87 to 95% by weight. When the battery electrode is the positive electrode, the content ratio of the conductive inorganic substance in the active material layer is usually 3 to 15% by weight, preferably 4 to 8%.
% By weight, and the content ratio of the lithium-containing oxide is usually 8
It is 0 to 95% by weight, preferably 85 to 92% by weight. Appropriate numerical values are selected for the content of the conductive inorganic substance and the content of the lithium-containing oxide from the above range so that the total amount becomes 100%.

What is important in the present invention is the organic solvent content, the water content, the variation in coating weight, and the ratio of the coating density to the average true density of the active material layer.

The battery electrode of the present invention can be manufactured by the method described below. At that time, the coating liquid for forming the active material layer applied to the conductor is dried,
The present inventors have found that the amount of residual organic solvent and the amount of moisture deteriorate the cycle characteristics of the secondary battery due to insufficient drying. At the same time, the present inventors also noticed that variations in the coating weight of the active material layer coating the surface of the conductor and the ratio of the coating density to the average true density have a great influence on the cycle characteristics of the secondary battery. The battery electrode of this invention is based on the above findings of the inventors.

What is important in the battery electrode of the present invention is that the content of the organic solvent in the active material layer is at most 200.
ppm, preferably at most 100 ppm, more preferably at most 50 ppm. When the content of the organic solvent remaining in the active material layer exceeds 200 ppm, the cycle characteristics of the secondary battery using the battery electrode of the present invention are particularly deteriorated, and the content of the organic solvent is 200 pp.
If it is up to m, the cycle characteristics of the secondary battery do not deteriorate so much as to be a problem in practical use. The water content in the active material layer is at most 100 ppm, preferably at most 50 ppm, and more preferably at most 3 ppm.
It is 0 ppm. When the content of water remaining in the active material layer exceeds 100 ppm, the cycle characteristics of the secondary battery using the battery electrode of the present invention are particularly deteriorated. If the content of water is up to 100 ppm, the secondary The cycle characteristics of the battery do not deteriorate so much as to pose a practical problem.

The content of the organic solvent and the content of the water can be determined by quantitative analysis using a mass spectrometer.

In the battery electrode of the present invention, the variation in the coating weight of the active material layer coating the surface of the conductor is at most 4%, preferably at most 3%, and more preferably at most 2%. is important.

Here, the meaning of the coating weight is as follows. That is, the coating weight is the weight per square centimeter of the active material layer coated on the conductor. Make sure that the area of the battery electrode on which the active material layer exists is the same.
Cut into equal parts, measure the weight (A) of each cut piece,
After that, the weight (B) of the remaining conductor after removing the active material layer from the conductor is measured, and (A)-(B) is divided by the electrode area to obtain the coating weight of each piece.

In the battery electrode of the present invention, the ratio (unit:%) of the coating density defined below to the average true density of the active material layer formed on the surface of the conductor is 45 to 9:
5%, preferably 50 to 92%, more preferably 60
It is important to be ~ 87%.

Here, the true density means a physical chemistry experimental method (19
55, published by Zenkabo Co., Ltd.), and is defined as the individual densities of the conductive inorganic substance and the binder forming the active material layer, which are measured by the method described on page 154. The average true density is the above-mentioned method. Determined by multiplying the individual densities of the conductive inorganic substance and the binder forming the active material layer measured in 1. by the weight fractions of the conductive inorganic substance and the binder in the active material layer, respectively, and adding them up. Is defined as

In the present invention, the active material layer formed on the surface of the conductor has the above-mentioned specific organic solvent content, water content, variation in coating weight, and ratio of coating density to average true density. A battery electrode capable of prolonging the cycle life of a secondary battery only when it is within a specific range can be realized.

<Battery Electrode Manufacturing Method> The battery electrode of the present invention is roughly prepared by preparing a dispersion liquid containing an active material layer, coating the dispersion liquid on the surface of a conductor, and A battery electrode can be formed by drying the dispersion applied on the surface to prepare an electrode, press-molding the obtained electrode, and then cutting the electrode into a shape suitable for a secondary battery.

The dispersion has a viscosity of 20 to 70 dPa.s, preferably 25 to 60 dPa.s, obtained by mixing the binder, the conductive inorganic substance and the organic solvent.
s, more preferably 35 to 50 dPa · s. When forming a battery electrode that is a positive electrode, it is preferable that the dispersion liquid further contains a lithium-containing oxide.

Here, when the viscosity of the dispersion liquid is adjusted within the above range, the dispersion of the coating weight of the active material layer covering the surface of the conductor becomes extremely small, and the layer thickness of the active material layer is reduced. The variation is also extremely small, and the battery electrode of the present invention can be suitably manufactured. In other words, when the viscosity of the dispersion liquid exceeds the upper limit value, the thickness of the active material layer varies greatly, and the coating weight also increases, and when the viscosity of the dispersion liquid falls below the lower limit value, it is practically sufficient. It becomes impossible to form a layer of the active material layer having a sufficient coating weight and coating density on the conductor.

Here, the viscosity of the dispersion liquid can be adjusted by adjusting the addition amount of the organic solvent. As this organic solvent, a non-aqueous polar solvent is preferable, and for example, N-methyl-2-pyrrolidone is preferable.

In the method of the present invention, the dispersion liquid adjusted to a predetermined viscosity is applied to the surface of the conductor.

The conductor is as described in the section of <Battery electrode>.

The thickness and application area of the dispersion liquid applied to the metal sheet are appropriately determined according to the scale of the secondary battery.

As a method for applying the dispersion liquid, brush coating,
Appropriate means such as dipping, coater coating, and spray coating are adopted.

After applying the dispersion on the surface of the conductor, the dispersion is dried. During this drying, the drying atmosphere is adjusted so that the oxygen concentration is at most 100 ppm, preferably at most 80 ppm.
It is preferable to use a deoxygenated atmosphere adjusted to ppm, more preferably 50 ppm. When the oxygen content in the atmosphere is within the above range, there is an advantage that the oxidation of the conductor can be remarkably suppressed even in the drying at a high temperature, which is preferable. The time for drying in the deoxygenated atmosphere is usually 5 to 60 minutes, preferably 10 to
40 minutes. The temperature during drying is usually 10
The temperature is 0 to 180 ° C, preferably 120 to 160 ° C.

As a more preferable mode of drying, there can be mentioned a multi-stage drying process in which preliminary drying is carried out at a low temperature in a low temperature air atmosphere, and then main drying is carried out at a high temperature in the deoxidized atmosphere. The multi-stage drying has an advantage that a relatively large amount of water and an organic solvent can be removed at the time of preliminary drying at a low temperature, so that the main drying time at a high temperature can be shortened.

The temperature for predrying is usually 80.
-120 degreeC, Preferably it is 95-115 degreeC. The predrying time is usually 5 to 20 minutes, preferably 10 to 15 minutes.

The temperature in the main drying is usually 100.
-180 degreeC, Preferably it is 120-160 degreeC. The main drying time is usually 2 to 20 minutes, preferably 5 to 10 minutes.

After the drying treatment, the obtained crude electrode body is further pressure-treated. As the pressure processing device, for example, a device such as a press machine or a roll press machine is used.

When a roll press is used as the pressure treatment device, pressing is performed with a clearance of 40 to 60% less than the thickness of the electrode laminate in which the surface of the conductor is coated with the active material layer. Is good.

<Secondary Battery> A secondary battery is formed from the battery electrode of the present invention and the non-aqueous electrolyte.

The non-aqueous electrolyte solution has a predetermined concentration of lithium salt.

As the lithium salt, LiClO ₄ ,
LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ S
O _{3 and the} like can be mentioned, and one of these can be used alone, or two or more of these can be used in combination. Of these, LiPF ₆ is preferable.

The concentration of the lithium salt is usually 0.8-
The amount is 2.0 mol / liter, preferably 1 to 1.8 mol / liter, and more preferably 1.2 to 1.7 mol / liter. When the concentration of the lithium salt is within the above range, there is an advantage that the secondary battery is excellent in cycle characteristics under high temperature and low temperature.

Further, the non-aqueous electrolytic solution contains lithium salt at a ratio of 0.8 to 2.0 mol / liter, represented by the following general formula (Formula 1).
It is contained in the organic carbonate compound represented by.

[0079]

Embedded image

(However, R ¹ and R ² each represent an alkyl group, which may be the same or different from each other, and R ¹ and R ² jointly form an oxygen atom and a carbon atom which are adjacent to each other. To form a ring.) As the organic carbonic acid compound represented by the general formula (Formula 1), propylene carbonate, ethylene carbonate,
Methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, etc. are mentioned.

The non-aqueous electrolyte in the secondary battery may be used by selecting one kind of the organic carbonic acid compounds, but preferably, at least three kinds of mixed solvents selected from the above organic carbonic acid compounds. The mixed solvent is not particularly limited as long as it is a mixture of three or more kinds of solvents selected from the organic carbonic acid compound, but a preferable mixed solvent is a mixed solvent composed of ethylene carbonate, propylene carbonate and diethyl carbonate, Examples of the mixed solvent include propylene carbonate, ethylene carbonate, and dimethyl carbonate, mixed solvent including ethylene carbonate, dimethyl carbonate, and diethyl carbonate, mixed solvent including propylene carbonate, ethylene carbonate, dimethyl carbonate, and diethyl carbonate. As a more preferable mixed solvent, a mixed solvent of three kinds consisting of ethylene carbonate, propylene carbonate and diethyl carbonate can be mentioned. In addition, in these mixed solvents,
Other additives or other organic solvents may be added.

When a mixed solvent of three kinds consisting of ethylene carbonate, propylene carbonate and diethyl carbonate is adopted, the mixing ratio of these is ethylene carbonate: propylene carbonate: diethyl carbonate = 2-5: 0.5-3.0 : 2.5 to 7.5
(Volume ratio) is preferable.

If the components of the organic solvent are three or more, the object of the present invention can be achieved well, and the advantage of high ionic conductivity even at low temperature is produced.

The non-aqueous electrolytic solution of the present invention can be obtained after the lithium salt is mixed in the organic solvent and stirred.

A secondary battery to which the battery electrode of the present invention is applied may be formed by the positive electrode which is the battery electrode of the present invention, the negative electrode which is the battery electrode of the present invention, and the non-aqueous electrolyte. it can.

In this secondary battery, it is preferable that the positive electrode and the negative electrode have the same capacity per unit area. The capacity per unit area is the capacity per unit weight of the active material layer obtained by a three-electrode type cell or a coin-type cell in which the counter electrode is metallic lithium, and the capacity per unit area provided on the conductor. It is calculated from the weight of the material layer.

Examples of the shape of the secondary battery using the non-aqueous electrolyte solution include button type secondary batteries, cylindrical type secondary batteries, square type secondary batteries, coin type secondary batteries and the like.

The cylindrical secondary battery is manufactured as follows.

The positive electrode and the negative electrode are rolled up with a separator made of a porous polypropylene sheet interposed therebetween. The roll is placed in a cylindrical battery can and the negative electrode lead wire is welded to the bottom of the can. Next, a positive electrode lead wire is welded to a positive electrode cap having a rupture disk, a closing lid, and a gasket. The electrolytic solution is put into the battery can, and the positive electrode cap is caulked to the opening of the negative electrode can. As a result, a cylindrical non-aqueous electrolyte secondary battery is obtained.

In the prismatic secondary battery, the same roll-shaped roll as in the cylindrical secondary battery is flattened, and the flattened product is housed in a prismatic can, or a positive electrode and a negative electrode to which lead wires are connected are attached. It can be produced by, for example, accommodating a laminate obtained by laminating it in a sandwich shape via a separator in a square can.

[0091]

【Example】

(Example 1) (1) Production of negative electrode A negative electrode was produced as follows. That is, 30 g of polyvinylidene fluoride (PVDF) was dissolved in 420 ml of N-methyl-2-pyrrolidone. In the obtained solution, graphitized vapor grown carbon fiber (average diameter; 2 μm, average fiber length; 20 μm, specific surface area; 1.8 m ² / g, carbon network plane distance d ₀₀₂ ; 0.3361 nm, carbon crystallite Thickness L
_c ; 120 nm, spin density; 7 × 10 ¹⁸ spins / s) 2
70 g was added and sufficiently dispersed with an ultrasonic disperser to obtain a dispersion liquid.

The dispersion was passed through a 40-mesh sieve and filtered. The filtered dispersion is
Vacuum degassing was performed at 0 mmHg. The dispersion viscosity at this time was 50 dPa · s.

A copper sheet (thickness: 10 μm,
It was applied to both sides (width 200 mm, length 3 m). The coated copper sheet is subjected to a dew point of −50 ° C. and an oxygen concentration of 50 ppm.
By drying at 150 ° C. for 15 minutes in an argon gas atmosphere, an electrode laminate in which the surface of the conductor was coated with the active material layer was obtained. The content ratio of the graphitized vapor-grown carbon fibers in the active material layer was 90% by weight.

The battery electrode, which is the negative electrode, was obtained by further cutting the above-mentioned electrode laminate into predetermined dimensions.

(2) Evaluation of Electrode The electrode laminate prepared in (1) above was evaluated. Even if this electrode laminate itself is evaluated as follows, the evaluation is equivalent to the evaluation of the characteristics of the negative electrode obtained by further cutting the electrode laminate.

The electrode laminate was made 39 mm wide and 45 mm long.
After cutting to 0 mm, the amount of residual solvent and the amount of water in the electrode were quantitatively analyzed by a mass spectrometer (manufactured by Nikkiso Co., Ltd .; MA-200).

After the quantitative analysis, the electrode was pressure-molded by a roll press machine with a clearance of 55% reduction with respect to the thickness of the electrode laminate. With respect to the electrode after pressure molding, the dispersion of the coating weight and the ratio of the coating density to the average true density were measured by the method described. Table 1 shows the results.

Example 2 (1) Production of Positive Electrode A positive electrode was produced as follows. PVDF 30g N
A solution was obtained by dissolving in 325 ml of methyl-2-pyrrolidone.

Next, 445 g of LiMn ₂ O ₄ , 15 g of artificial graphite and 10 g of acetylene black were mixed and sufficiently dispersed by an ultrasonic disperser to obtain a dispersion liquid.

The dispersion was passed through a 40-mesh sieve and the dispersion was filtered. The filtered dispersion is
Vacuum degassing was performed at 0 mmHg. The viscosity of the dispersion liquid at this time was 48 dPa · s.

The dispersion was applied to both sides of an aluminum sheet (thickness 20 μm, width 200 mm, length 3 m). The coated aluminum sheet is preliminarily dried in an air atmosphere at 110 ° C., and then dried at 150 ° C. in an argon gas atmosphere having a dew point of −50 ° C. and an oxygen concentration of 50 ppm.
After drying for minutes, an electrode laminate in which the surface of the conductor was coated with the active material layer was obtained. The content ratio of the conductive inorganic substances (artificial graphite and acetylene black) in this active material layer was 5% by weight, and the content ratio of LiMn ₂ O ₄ was 89% by weight.

The battery electrode serving as the positive electrode was obtained by further cutting the above electrode laminate to a predetermined size.

(2) Evaluation of Electrode As in Example 1, the amount of residual solvent in the electrode, the amount of water, the variation in coating weight, and the ratio of the coating density to the average true density were measured. The measurement results are shown in Table 1.

Example 3 (1) Preparation of Cylindrical Battery Using the electrode prepared in Example 1 as a negative electrode and the electrode prepared in Example 2 as a positive electrode, a cylindrical battery was prepared as follows.

First, the electrode laminate prepared in (1) of Example 1 was cut into a width of 39 mm and a length of 450 mm, which was used as a negative electrode.

Similarly, the electrode laminate produced in (1) of Example 2 was cut into a width of 38 mm and a length of 430 mm,
This was used as the positive electrode.

The positive electrode and the negative electrode were wound up in a roll shape with a porous propylene sheet separator interposed therebetween. This roll-shaped roll is 16 mm in diameter and 50 mm in height.
And the negative electrode lead wire was welded to the bottom of the can. Next, a positive electrode lead wire was welded to a positive electrode cap having a rupture disk, a closing lid, and a gasket. In the battery can, a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) (volume ratio; EC / PC / DEC =) was added so that LiPF ₆ had a concentration of 1.3 mol. An electrolytic solution prepared by dissolving in 3/1/6) was put, and the positive electrode cap was caulked in the opening of the negative electrode can. As a result, a cylindrical secondary battery was obtained.

(2) Cycle test with cylindrical battery Charge / discharge current of 600 mA, charge / discharge voltage of 2.5 to 4.2
As V, the charging / discharging of the cylindrical secondary battery was performed 100 cycles. The measurement temperature at this time was 21 ° C. The discharge capacities at the first cycle, the 50th cycle and the 100th cycle were measured, and the results are shown in Table 2.

Example 4 (1) Preparation of Electrode (Negative Electrode) Using the same dispersion liquid (viscosity 50 dPa · S) prepared in (1) of Example 1 as shown in FIG. The copper coating was continuously applied onto the copper box 3 (thickness 10 μm, width 200 mm, length about 300 m) by the die coater 1. The inside of the work chamber 2 was an atmosphere of dry air with a dew point of −55 ° C.

After coating the surface with a coating speed of 20 cm / min and continuously passing it through the first drying chamber 4 (temperature: 105 ° C., effective length: 2 m), the surface-coated copper was rolled by a roll 5 with a copper box interposed. Invert and apply the dispersion to the back with the same thickness as the front,
It was passed through the second drying chamber 6 (temperature 110 ° C., effective length 2 m).

Further, the temperature of 155 ° C. and the effective length of 5 m
Drying chamber 7 (using 99.999% nitrogen and having two upper and lower rolls 8 and 9 having a gap to allow a coated copper box to pass therethrough in order to keep airtightness) is passed through. Then, it was cut into 39 mm in width by a slitter 10 and wound into four long electrodes. The wound material was further passed through a press roll 11 and wound.

(2) Preparation of Electrode (Positive Electrode) The same dispersion liquid as in (1) of Example 2 was applied to aluminum foil (thickness: 20 μm).
m, width 200 mm, length about 300 mm) (1)
Coating and press roll application were carried out under exactly the same conditions as in the production of the negative electrode of Example 1 to produce four long electrodes.

(3) Evaluation of Electrode The amount of residual solvent, water content, electrode thickness, electrode weight and coating density of the electrodes prepared in (1) and (2) above were measured in the same manner as in Example 1. . It was confirmed that the measured values were substantially the same as those in Example 1 and Example 2 in Table 1.

Comparative Example 1 (1) Preparation of Electrode A dispersion was prepared in the same manner as in Example 1 to prepare a copper sheet (thickness 1
0 μm, width 200 mm, length 3 m).
The copper sheet was dried at 140 ° C. in an air atmosphere. After drying, an electrode was obtained.

When the electrode was observed after drying, the uncoated portion of the copper sheet turned reddish brown (oxidized). It was not qualified as an electrode.

Comparative Example 2 (1) Preparation of Electrode A dispersion was prepared in the same manner as in Example 1 to prepare a copper sheet (thickness 1
0 μm, width 200 mm, length 3 m).
The copper sheet was dried at 110 ° C. in an air atmosphere. After drying, an electrode was obtained.

(2) Evaluation of Electrode As in Example 1, the amount of residual solvent in the electrode, the amount of water, the variation in coating weight, and the ratio of the coating density to the average true density were measured.

The measurement results are shown in Table 1.

Comparative Example 3 (1) Preparation of Electrode An electrode was prepared as follows. That is, 30 g of polyvinylidene fluoride (PVDF) was dissolved in 300 ml of N-methyl-2-pyrrolidone. In the obtained solution, graphitized vapor grown carbon fiber (average diameter; 2 μm, average fiber length; 20 μm, specific surface area; 1.8 m ² / g, carbon network plane distance d ₀₀₂ ; 0.3361 nm, carbon crystallite Thickness L
_c ; 120 nm, spin density; 7 × 10 ¹⁸ spins / s) 2
70 g was added and sufficiently dispersed with an ultrasonic disperser to obtain a dispersion liquid.

The dispersion was filtered through a 40-mesh screen and filtered. The filtered dispersion is
Vacuum degassing was performed at 0 mmHg. The viscosity of the dispersion liquid at this time was 80 dPa · s.

A copper sheet (thickness: 10 μm,
It was applied to both sides (width 200 mm, length 3 m). The coated copper sheet is subjected to a dew point of −50 ° C. and an oxygen concentration of 50 ppm.
Under an argon gas atmosphere at 150 ° C. After drying, an electrode laminate was obtained in which the surface of the conductor was coated with the active material layer. The content ratio of the graphitized vapor grown carbon fiber in this active material layer was 90% by weight.

(2) Evaluation of Electrode As in Example 1, the amount of residual solvent in the electrode, the amount of water, the variation in coating weight, and the ratio of the coating density to the average true density were measured.

The measurement results are shown in Table 1.

Comparative Example 4 (1) Preparation of Electrode A positive electrode was prepared as follows. 30 g of polyvinylidene fluoride (PVDF) was added to N-methyl-2-pyrrolidone 4
It was dissolved in 50 ml to obtain a solution.

Next, 445 g of LiMn ₂ O ₄ , 15 g of artificial graphite and 10 g of acetylene black were mixed and sufficiently dispersed by an ultrasonic disperser to obtain a dispersion liquid.

The dispersion was filtered through a 40-mesh sieve and the dispersion was filtered. The filtered dispersion is
Vacuum degassing was performed at 0 mmHg. The viscosity of the dispersion liquid at this time was 15 dPa · s.

The dispersion was applied to both sides of an aluminum sheet (thickness 20 μm, width 200 mm, length 3 m). The coated aluminum sheet is pre-dried in an air atmosphere at 110 ° C., and then 150 ° C. in an argon gas atmosphere having a dew point of −50 ° C. and an oxygen concentration of 50 ppm.
And dried. After drying, an electrode laminate was obtained in which the surface of the conductor was coated with the active material layer. The content ratio of the conductive inorganic substances (artificial graphite and acetylene black) in this active material layer was 5% by weight, and the content ratio of LiMn ₂ O ₄ was 89% by weight.

(2) Evaluation of Electrode As in Example 1, the amount of residual solvent in the electrode, the amount of water, the dispersion of the coating weight, and the ratio of the coating density to the average true density were measured.

The measurement results are shown in Table 1.

Comparative Example 5 (1) Preparation of Cylindrical Battery A cylindrical battery was prepared in the same manner as in Example 3 except that the electrode prepared in Comparative Example 2 was the negative electrode and the electrode prepared in Comparative Example 4 was the positive electrode.

(2) Cycling Test with Cylindrical Battery A cycling test was conducted in the same manner as in Example 3, and the results are shown in Table 2.

[0132]

[Table 1]

[0133]

[Table 2]

[0134]

According to the present invention, the cycle life is long,
A battery electrode suitable for a secondary battery having excellent charge / discharge efficiency can be provided.

According to the present invention, the cycle life is long,
A battery electrode manufacturing method capable of easily manufacturing a battery electrode suitable for a secondary battery having excellent charge / discharge efficiency by adding a simple operation of adjusting viscosity can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an electrode manufacturing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Roll type coating machine, 2 ... Working room, 3 ... Copper box, 4 ... First drying room, 5 ... Roll, 6 ... Second drying room, 7 ... .... Third drying chamber, 8, 9 ... Rolls,
10 ... slitter, 11 ... press roll.

Claims (6)

[Claims] 1. A surface of a conductor is coated with an active material layer containing a conductive inorganic substance and a binder, and the content of the organic solvent in the active material layer is at most 200 ppm,
The water content in the active material layer is at most 100 ppm, the coating weight variation of the active material layer defined below is at most 4%, and the active material layer is defined below. An electrode for a battery, characterized in that the ratio (unit:%) of the coating density defined below with respect to the average true density is 45 to 95%. Coating weight: The weight of the active material layer per square centimeter covering the conductor. Variation in coating weight: [(average coating weight-coating weight) / average coating weight] x 100 Average true density: The true density of each material forming the active material layer is multiplied by the weight fraction of each material in the active material layer. , The sum of them. True density: The density of the material itself. Coating density: Density of the active material layer coated with the conductor. 2. The battery electrode according to claim 1, wherein the conductive inorganic substance is a carbon material. 3. The battery electrode according to claim 1, wherein the conductive inorganic substance is vapor grown carbon fiber. 4. The conductive inorganic material is a carbon material,
The battery electrode according to claim 1, wherein the active material layer further contains a lithium-containing oxide. 5. A dispersion liquid containing a binder, a conductive inorganic substance, and an organic solvent and having a viscosity adjusted to 20 to 70 dPa · s is prepared, and the dispersion liquid is applied to a conductor and then applied to the conductor. A method for producing a battery electrode, characterized in that an active material layer-covered conductor is obtained by drying the dispersion thus obtained, and the active material layer-covered conductor is pressure-molded. 6. The method for producing a battery electrode according to claim 5, wherein the dispersion liquid applied to the conductor is dried in an oxygen-containing atmosphere having an oxygen concentration of at most 100 ppm.