JP2003157836A - Manufacturing method of positive electrode for lithium battery and positive electrode for lithium battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a positive electrode for a lithium battery without causing corrosion in a collector even if a solvent comprising water is used for active material paste. SOLUTION: This manufacturing method of a positive electrode for a lithium battery has a process for preparing active material paste, and a process for forming an active material mix layer. In this case, the manufacturing method of the positive electrode for a lithium battery is characterized in that a positive electrode active material has, on its surface, a protective coating capable of restraining reaction with water and having electric conductivity. In the manufacturing method of the positive electrode for a lithium battery, since the protective coating formed on the surface of the positive electrode active material restrains elution of lithium from the positive electrode active material, the reaction of the active material paste with the collector is restrained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a positive electrode for a lithium battery and a positive electrode for a lithium battery.

[0002]

2. Description of the Related Art In recent years, as a power source for electric devices such as mobile phones and portable video cameras, a lithium battery is becoming mainstream because of its high weight energy density.
This lithium battery has a positive electrode having a positive electrode active material containing lithium and capable of releasing lithium as lithium ions during charging and occluding lithium ions during discharging,
Consists of a negative electrode that has a negative electrode active material and is capable of occluding lithium ions during charging and releasing lithium ions during discharging, and a non-aqueous electrolytic solution in which an electrolyte composed of a supporting salt containing lithium in an organic solvent is dissolved. To be done.

Further, in such a lithium battery, in order to improve the weight energy density, the positive electrode and the negative electrode are formed in a sheet shape, and the sheet-shaped positive electrode and the negative electrode are formed through a separator which is also formed in the sheet shape. It is housed in a case in a wound or laminated state. The sheet-shaped positive electrode and negative electrode each have a structure in which a mixture layer containing an active material is formed on the surface of a metal foil serving as a current collector.

The positive electrode of the lithium battery is LiMexOy.
(Me; a transition metal containing at least one of Ni, Co and Mn, x and y are not particularly limited),
Conductive agent made of carbon, carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTF
It is manufactured by preparing an active material paste in which a binder made of E) or the like is dispersed in a solvent, and applying the adjusted active material paste to the surface of a current collector made of Al to form a mixture layer. .

In the production of positive electrodes for lithium batteries, an organic solution such as NMP has been used as a solvent. On the other hand, in recent years, water has been used as a solvent in order to reduce the cost required for raw materials and handling and the environmental load at the time of discharge.

LiMexOy, which is a positive electrode active material, is known to react with water. That is, LiMe in water
When xOy is added, Li in the crystal is released. It is speculated that this reaction occurs due to ion exchange between Li ions (Li ⁺ ) in the crystal and protons (H ⁺ ) of water.

Further, LiMexOy is added to a solvent consisting of water.
The active material paste in which is dispersed exhibits alkalinity due to the elimination of Li ions. The alkaline active material paste reacts with the current collector to promote corrosion of the current collector and generation of H ₂ gas.

When H ₂ gas is generated at the interface between the current collector and the active material paste, the active material is lifted up. As a result of the floating, the apparent volume of the active material increases and the weight per unit volume decreases. When the coating property is reduced in this way, the coating density is reduced.

Further, in the mixture layer of the manufactured electrode,
Many holes having an inner diameter of about several tens of μm are formed by the H ₂ gas.
The large number of holes cause cracks on the surface of the mixture layer, which lowers the strength of the electrode body. Further, the material distribution of the mixture layer becomes non-uniform, and battery characteristics such as cycle characteristics deteriorate.

Furthermore, in order to manufacture the positive electrode and the mixture layer in a short time, the active material paste applied to the surface of the current collector is heated and dried. However, by heating for drying, the Li ion desorption reaction and the reaction between the alkaline active material paste and Al of the current collector are further promoted. Therefore, the drying speed cannot be increased, and the time required to manufacture the positive electrode is long.

In order to solve such a problem, Japanese Patent Application Laid-Open No. 8-69791 discloses a method of mixing carbon dioxide gas in an active material paste to neutralize it.

More specifically, Japanese Patent Laid-Open No. 8-69791 discloses that
Using a metal foil that is corrosive to strong alkalis as a current collector,
A positive electrode plate having an active material layer containing a composite oxide containing lithium and a transition metal as a main component on its surface, a negative electrode plate, and a non-aqueous liquid having a separator interposed between the positive electrode plate and the negative electrode plate. In the method for manufacturing an electrolytic solution secondary battery, the positive electrode plate neutralizes an alkaline component of a viscous aqueous solution obtained by kneading an active material and a thickener, and then coats this paste on a current collector surface and dry it. A method of manufacturing a non-aqueous electrolyte secondary battery characterized by the above is disclosed.

However, the method of supplying carbon dioxide gas into the active material paste to neutralize it has a problem that the amount of Li released from LiMexOy becomes large. That is, since a large amount of Li leaves LiMexOy, L
There has been a problem that the composition and crystal structure of iMexOy are changed and the battery characteristics are deteriorated.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and is a method for producing a positive electrode for a lithium battery in which the current collector is not corroded even when a solvent made of water is used for the active material paste. The challenge is to provide.

[0015]

In order to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using an active material having a protective coating on the surface which suppresses the reaction between the active material paste and water. I found it.

That is, the method for producing a positive electrode for a lithium battery of the present invention is based on LiMexOy (Me; Ni, Co, Mn).
Of a transition metal containing at least one of x, y; any) and a step of preparing an active material paste having water, and applying the active material paste to the surface of a current collector made of Al. And a step of forming an active material mixture layer by drying, and a method for producing a positive electrode for a lithium battery,
The positive electrode active material is characterized by having on its surface a protective coating that suppresses reaction with water and has electrical conductivity.

In the method for producing a positive electrode for a lithium battery of the present invention, since the protective coating is formed on the surface of the positive electrode active material, the elution of lithium from the positive electrode active material is suppressed even when the active material paste is formed. There is. Therefore, the reaction between the active material paste and the current collector is suppressed. As a result, the positive electrode for a lithium battery manufactured by the method for manufacturing a positive electrode for a lithium battery of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode manufactured using the manufacturing method of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

The positive electrode for a lithium battery of the present invention is LiMe
xOy (Me; transition metal containing at least one of Ni, Co, and Mn, x, y; optional), a step of preparing an active material paste having water, and a positive electrode active material, and a current collector made of Al A positive electrode active material for a lithium battery, comprising a step of applying an active material paste on a surface of a body and drying the active material mixture layer to form a positive electrode for a lithium battery. Is characterized by having on its surface a protective coating that suppresses reaction with water and has electrical conductivity.

In the positive electrode for a lithium battery of the present invention, since the positive electrode active material is not eluted in the active material paste, the reaction between the active material paste and the current collector is suppressed, and the positive electrode active material is uniformly dispersed. A mixture layer is formed. That is,
The positive electrode for a lithium battery of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

The method for producing a positive electrode for a lithium battery according to the present invention comprises a positive electrode active material made of LiMexOy (Me; transition metal containing at least one of Ni, Co and Mn, x, y; any), water, and And a step of applying an active material paste to the surface of a current collector made of Al, and drying to form an active material mixture layer,
In the method for producing a positive electrode for a lithium battery having the above, the positive electrode active material has a protective coating having a pH of less than 11.5 when mixed with water.

The method for producing a positive electrode for a lithium battery according to the present invention has a protective coating having a pH of less than 11.5 when the positive electrode active material is mixed with water, so that the p of the active material paste is
Since H is less than 11.5, corrosion of the current collector due to the active material paste is suppressed. As a result, the positive electrode for a lithium battery manufactured by the manufacturing method of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode manufactured using the manufacturing method of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

The positive electrode for a lithium battery of the present invention is LiMe
xOy (Me; transition metal containing at least one of Ni, Co, and Mn, x, y; optional), a step of preparing an active material paste having water, and a positive electrode active material, and a current collector made of Al A positive electrode active material for a lithium battery, comprising a step of applying an active material paste on a surface of a body and drying the active material mixture layer to form a positive electrode for a lithium battery. Has a protective coating having a pH of less than 11.5 when mixed with water.

In the positive electrode for a lithium battery of the present invention, when the active material paste is applied to the surface of the current collector, corrosion of the current collector by the active material paste is suppressed. As a result, the positive electrode for a lithium battery of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode for a lithium battery of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION [First Invention] (Manufacturing Method) A method for manufacturing a positive electrode for a lithium battery according to the present invention comprises a LiMexOy (Me; transition metal containing at least one of Ni, Co and Mn, x, y; A step of preparing an active material paste having a positive electrode active material consisting of (optional) and water, and applying the active material paste onto the surface of a current collector consisting of Al and drying to form an active material mixture layer. In the method for producing a positive electrode for a lithium battery including the step, the positive electrode active material has a protective coating that suppresses reaction with water and has electrical conductivity on the surface.

LiMexOy (Me; Ni, Co, Mn
In the step of preparing an active material paste having a positive electrode active material made of a transition metal containing at least one of x, y; and arbitrary) and water, an active material paste using water as a solvent is prepared.

The active material mixture layer is formed on the surface of the current collector by the step of applying the active material paste on the surface of the current collector made of Al and drying it to form the active material mixture layer. For the positive electrode.

The positive electrode active material has on its surface a protective coating that suppresses the reaction with water and has electrical conductivity. Since the positive electrode active material has the protective coating, the elution of lithium from the positive electrode active material in the active material paste can be suppressed. By suppressing the elution of lithium, it is possible to prevent the active material paste from becoming alkaline, which can corrode aluminum. Therefore, the reaction between the active material paste and the current collector is suppressed, and a positive electrode for a lithium battery having a uniform active material mixture layer can be manufactured.

The protective coating is preferably made of a hydrophobic material. Since the protective film is made of a hydrophobic material,
In the active material paste, the reaction between the positive electrode active material and water is suppressed.

The protective coating preferably does not interfere with the migration of lithium ions when the battery is assembled. That is, if the protective film formed on the surface of the positive electrode active material inhibits the movement of lithium ions, the electrode reaction in the positive electrode active material does not occur. An example of such a protective film is a protective film having pores through which lithium ions can pass.

The protective coating preferably has carbon. Since carbon does not react with water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Further, as can be seen from the fact that carbon is introduced as a conductive agent in the active material mixture layer in an ordinary lithium battery, not only does it not decompose at the battery potential, but also the current collector and the positive electrode active material. Has the property of helping the electrical conduction of. Therefore, it becomes a stable protective film.

The protective coating preferably comprises polytetrafluoroethylene (PTFE). Since PTFE has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Also, PT
FE is stable in the working potential range of the electrode,
Does not decompose when using batteries. Therefore, deterioration of the active material mixture layer can be suppressed. Further, since PTFE is not easily dissolved in the electrolytic solution, deterioration of the electrode due to the protective film being dissolved in the electrolytic solution when the battery is formed can be suppressed. As can be seen from the fact that this PTFE is introduced as a binder that binds the positive electrode active material to the active material mixture layer in an ordinary lithium battery, it does not interfere with the electrode reaction of the positive electrode active material, It also functions as a glue.

The protective coating preferably comprises a conductive polymer. Since the conductive polymer has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. As this conductive polymer,
For example, polyaniline can be mentioned.

In the method for producing a positive electrode for a lithium battery of the present invention, the method for forming the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the method for producing a positive electrode for a lithium battery of the present invention is characterized by using a positive electrode active material having a protective coating, and the method for forming the protective coating is not limited. As the method for forming the protective film, for example, a method in which a positive electrode active material and a material forming the protective film are dispersed or dissolved in a solution to perform coating, and a solid phase reaction occurs between the positive electrode active material and the material forming the protective film. Examples thereof include a coating method and a method of depositing a material for forming a protective film on the positive electrode active material.

The protective coating is preferably formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective coating. That is, by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film, the protective film can be formed by a solid phase reaction. That is, since the protective film can be formed without using a solvent, increase in cost required for materials and manufacturing can be suppressed.

In the method for producing a positive electrode for a lithium battery of the present invention, the thickness of the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the characteristics of the protective coating itself differ depending on the material used, and thus the thickness required for inhibiting the reaction with water differs.

The method for producing the positive electrode for a lithium battery of the present invention is not particularly limited except that the surface of the positive electrode active material has a protective coating. That is, as a material forming the active material paste, a material used for manufacturing a conventional positive electrode for a lithium battery can be used.

The positive electrode active material LiMexOy (Me; N
i, Co, transition metal containing at least one of Mn, x,
y; arbitrary) is not particularly limited. For example, LiMnO ₂ , LiMn ₂ O ₄ , LiCoO ₂ , LiN
A compound in which various metal elements are substituted with iO ₂ as a main skeleton can be used.

LiMn ₂ O ₄ system, LiCoO ₂ system, Li
A NiO ₂ -based positive electrode active material is more preferable. That is, since it has excellent performance as a positive electrode active material such as excellent diffusion performance of electrons and lithium ions, a lithium battery having high charge / discharge efficiency and good cycle characteristics can be obtained.

For example, the reactivity of the positive electrode active material with water is
The order is LiNiO ₂ system> LiCoO ₂ system> LiMn ₂ O ₄ system, and the production method of the present invention exerts a particularly large effect when a LiNiO ₂ system positive electrode active material is used.

The active material paste preferably contains a binder and / or a conductive agent. When the active material paste has the binder and / or the conductive agent, the characteristics of the manufactured positive electrode are improved.

The binder has a function of binding the positive electrode active material particles. As the binder, a water-soluble polymer or emulsion can be used, and for example, carboxymethyl cellulose (CMC), methyl cellulose, polyethylene oxide, hydroxyethyl cellulose can be used alone or in combination.

The conductive agent ensures the electric conductivity of the positive electrode.
Examples of the conductive agent include one or a mixture of two or more carbon substances such as carbon black, acetylene black, and graphite.

In the method for producing a positive electrode for a lithium battery of the present invention, since the protective coating is formed on the surface of the positive electrode active material, the elution of lithium from the positive electrode active material is suppressed even when the active material paste is formed. There is. Therefore, the reaction between the active material paste and the current collector is suppressed. As a result, the positive electrode for a lithium battery manufactured by the method for manufacturing a positive electrode for a lithium battery of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode manufactured using the manufacturing method of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

(Lithium Battery Positive Electrode) The lithium battery positive electrode of the present invention is made of LiMexOy (Me; Ni, Co, M).
a step of preparing an active material paste having a positive electrode active material composed of a transition metal containing at least one kind of n, x, y; any), and water; and the active material paste on the surface of a current collector composed of Al. A method for producing a positive electrode for a lithium battery, which comprises the steps of applying and drying to form an active material mixture layer, wherein the positive electrode active material suppresses a reaction with water. And has a protective coating having electrical conductivity on the surface.

In the positive electrode for a lithium battery of the present invention, since the active material paste and the positive electrode active material are prevented from reacting with each other during the production of the positive electrode, the positive electrode active material is uniformly dispersed. That is, the positive electrode for a lithium battery of the present invention can exhibit high battery characteristics when a lithium battery is formed.

LiMexOy (Me; Ni, Co, Mn
In the step of preparing an active material paste having a positive electrode active material made of a transition metal containing at least one of x, y; and arbitrary) and water, an active material paste using water as a solvent is prepared.

By the step of applying the active material paste on the surface of the current collector made of Al and drying it to form the active material mixture layer, the active material mixture layer is formed on the surface of the current collector, and the lithium battery is formed. For the positive electrode.

The positive electrode active material has on its surface a protective coating that suppresses the reaction with water and has electrical conductivity. That is, since the lithium battery positive electrode of the present invention has the protective coating on the surface of the positive electrode active material, the reaction between the positive electrode active material and water is suppressed when the active material paste is prepared.

That is, since the positive electrode for a lithium battery of the present invention has the protective coating on the surface of the current collector, the reaction between the current collector and the active material paste occurs in the step of forming the active material mixture layer during the production. Is suppressed.

The protective film is preferably made of a hydrophobic material. Since the protective film is made of a hydrophobic material,
In the active material paste, the reaction between the positive electrode active material and water is suppressed.

The protective coating preferably does not interfere with the migration of lithium ions when the battery is assembled. That is, if the protective film formed on the surface of the positive electrode active material inhibits the movement of lithium ions, the electrode reaction in the positive electrode active material does not occur. An example of such a protective film is a protective film having pores through which lithium ions can pass.

The protective film preferably contains carbon. Since carbon does not react with water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Further, as can be seen from the fact that carbon is introduced as a conductive agent in the active material mixture layer in an ordinary lithium battery, not only does it not decompose at the battery potential, but also the current collector and the positive electrode active material. Has the property of helping the electrical conduction of. Therefore, it becomes a stable protective film.

The protective coating preferably comprises polytetrafluoroethylene (PTFE). Since PTFE has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Also, PT
FE is stable in the working potential range of the electrode,
Does not decompose when using batteries. Therefore, deterioration of the active material mixture layer can be suppressed. Further, since PTFE is not easily dissolved in the electrolytic solution, deterioration of the electrode due to the protective film being dissolved in the electrolytic solution when the battery is formed can be suppressed. As can be seen from the fact that this PTFE is introduced as a binder that binds the positive electrode active material to the active material mixture layer in an ordinary lithium battery, it does not interfere with the electrode reaction of the positive electrode active material, It also functions as a glue.

The protective coating preferably comprises a conductive polymer. Since the conductive polymer has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. As this conductive polymer,
For example, polyaniline can be mentioned.

In the lithium battery positive electrode of the present invention, the method for forming the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the positive electrode for a lithium battery of the present invention is characterized by using a positive electrode active material having a protective coating, and the method for forming the protective coating is not limited. As the method for forming the protective film, for example, a method in which a positive electrode active material and a material forming the protective film are dispersed or dissolved in a solution to perform coating, and a solid phase reaction occurs between the positive electrode active material and the material forming the protective film. Examples thereof include a coating method and a method of depositing a material for forming a protective film on the positive electrode active material.

The protective coating is preferably formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective coating. That is, by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film, the protective film can be formed by a solid phase reaction. That is, since the protective film can be formed without using a solvent, increase in cost required for materials and manufacturing can be suppressed.

In the positive electrode for a lithium battery of the present invention, the thickness of the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the characteristics of the protective coating itself differ depending on the material used, and thus the thickness required for inhibiting the reaction with water differs.

The positive electrode for a lithium battery of the present invention is not particularly limited, except that it has a protective coating on the surface of the positive electrode active material. That is, as a material forming the active material paste, a material used for manufacturing a conventional positive electrode for a lithium battery can be used.

The positive electrode active material LiMexOy (Me; N
i, Co, transition metal containing at least one of Mn, x,
y; arbitrary) is not particularly limited. For example, LiMnO ₂ , LiMn ₂ O ₄ , LiCoO ₂ , LiN
A compound in which various metal elements are substituted with iO ₂ as a main skeleton can be used.

LiMn ₂ O ₄ system, LiCoO ₂ system, Li
A NiO ₂ -based positive electrode active material is more preferable. That is, since it has excellent performance as a positive electrode active material such as excellent diffusion performance of electrons and lithium ions, a lithium battery having high charge / discharge efficiency and good cycle characteristics can be obtained.

For example, the reactivity of the positive electrode active material with water is
The order is LiNiO ₂ system> LiCoO ₂ system> LiMn ₂ O ₄ system, and the production method of the present invention exerts a particularly large effect when a LiNiO ₂ system positive electrode active material is used.

The active material paste preferably contains a binder and / or a conductive agent. When the active material paste has the binder and / or the conductive agent, the characteristics of the manufactured positive electrode are improved.

The binder has a function of binding the positive electrode active material particles together. As the binder, a water-soluble polymer or emulsion can be used, and for example, carboxymethyl cellulose (CMC), methyl cellulose, polyethylene oxide, hydroxyethyl cellulose can be used alone or in combination.

The conductive agent ensures the electric conductivity of the positive electrode.
Examples of the conductive agent include one or a mixture of two or more carbon substances such as carbon black, acetylene black, and graphite.

In the positive electrode for a lithium battery of the present invention, since the positive electrode active material is not eluted in the active material paste, the reaction between the active material paste and the current collector is suppressed and the positive electrode active material is uniformly dispersed. A mixture layer is formed. That is,
The positive electrode for a lithium battery of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

(Lithium Battery) The positive electrode manufactured by the method for manufacturing a positive electrode for a lithium battery of the present invention and the positive electrode for a lithium battery of the present invention can form a lithium battery in the same manner as a normal positive electrode for a lithium battery. .

That is, it can be manufactured by housing the positive electrode and the negative electrode together with the electrolytic solution in the battery container.

The negative electrode is not particularly limited in its material structure as long as it can absorb lithium ions during charging and release lithium ions during discharging, and known materials can be used. In particular, it is preferable to use a mixture obtained by mixing the negative electrode active material and the binder and applying the mixture to the current collector.

The negative electrode active material is not particularly limited, and a known active material can be used. For example, carbon materials such as highly crystalline natural graphite and artificial graphite,
Examples thereof include metallic lithium, lithium alloys, metallic materials such as tin compounds, and conductive polymers.

The binder has a function of binding the active material particles. As the binder, an organic binder or an inorganic binder can be used. For example, carboxymethyl cellulose (CMC), styrene butadiene rubber (S
BR) can be used alone or in combination.

As the current collector of the negative electrode, for example, a net, punched metal, foam metal or a foil processed into a plate shape of copper, nickel or the like can be used.

The electrolytic solution may be any electrolytic solution used in ordinary lithium secondary batteries, and is composed of an electrolyte salt and a non-aqueous solvent.

Examples of the electrolyte salt include LiP
F₆, LiBF_Four, LiClO_Four, LiAsF₆, LiC
l, LiBr, LiCF₃SO₃, LiN (CF₃S
O₂)₂, LiC (CF₃SO₂)₃, LiI, LiAlC
l_Four, NaClO_Four, NaBF_Four, Nal, etc.
And especially LiPF₆, LiBF_Four, LiClO_Four,
LiAsF₆Inorganic lithium salts such as LiN (SO₂C_x
F_{2x + 1}) (SO₂C_yF_{2y + 1}) Organic lithium salt represented by
Can be raised. Where x and y are 1 to 4
It represents an integer, and x + y is 3 to 8. Organic richiu
Specifically, LiN (SO₂CF₃)
(SO₂C₂F_Five), LiN (SO₂CF₃) (SO₂C
₃F ₇), LiN (SO₂CF₃) (SO₂C_FourF₉), Li
N (SO₂C₂F_Five) (SO₂C ₂F_Five), LiN (SO₂C₂
F_Five) (SO₂C₃F₇), LiN (SO₂C₂F_Five) (SO₂
C_FourF₉) Etc. Among them, LiN (SO₂C
F₃) (SO₂C_FourF₉), LiN (SO₂C₂F_Five) (SO
₂C₂F_Five) Is used as the electrolyte, it has excellent electrical characteristics.
It is preferable because

The organic solvent in which the electrolyte salt is dissolved is not particularly limited as long as it is an organic solvent used for a non-aqueous electrolyte of a usual lithium secondary battery, and examples thereof include carbonate compounds, lactone compounds, ether compounds and sulfolane compounds. , Dioxolane compounds, ketone compounds, nitrile compounds, halogenated hydrocarbon compounds and the like. Specifically, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, carbonates such as vinylene carbonate, lactones such as γ-butyl lactone, Ethers such as dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, sulfolanes such as sulfolane and 3-methylsulfolane, dioxolanes such as 1,3-dioxolane, 4-methyl-2- Ketones such as pentanone, acetonitrile,
Examples thereof include nitriles such as pyropionitrile, valeronitrile and benzonitrile, halogenated hydrocarbons such as 1,2-dichloroethane, and other methyl formate, dimethylformamide, diethylformamide, dimethyl sulfoxide and the like. Further, it may be a mixture thereof.

Among these organic solvents, one or more non-aqueous solvents selected from the group consisting of carbonates are
It is preferable because it has excellent solubility, dielectric constant and viscosity of the electrolyte.

The lithium battery formed by using the positive electrode is
The shape is not particularly limited, and it can be used as a battery of various shapes such as a sheet type, a coin type, a cylindrical type, and a square type. It is preferable that the positive electrode and the negative electrode are formed in a sheet shape, and the wound electrode body is wound with a sheet separator interposed therebetween. Furthermore, since it is excellent in volumetric efficiency, a flat wound electrode body is more preferable.

The separator is not particularly limited as long as it is a separator used in a normal lithium secondary battery, and examples thereof include a porous resin made of polyethylene, polypropylene or the like.

The lithium battery formed by using the positive electrode is
Since the cycle characteristics of the positive electrode are not deteriorated, the cycle characteristics are excellent.

[Second Invention] (Production Method) The production method of the positive electrode for a lithium battery of the present invention comprises LiMexOy (Me; a transition metal containing at least one of Ni, Co and Mn, x, y; any). A step of preparing an active material paste having a positive electrode active material and water; and a step of applying the active material paste on the surface of a current collector made of Al and drying it to form an active material mixture layer. In the method for producing a positive electrode for a lithium battery having the positive electrode active material, the positive electrode active material has a protective coating having a pH of less than 11.5 when mixed with water.

LiMexOy (Me; Ni, Co, Mn
In the step of preparing an active material paste having a positive electrode active material made of a transition metal containing at least one of x, y; and arbitrary) and water, an active material paste using water as a solvent is prepared.

By the step of applying the active material paste on the surface of the current collector made of Al and drying it to form the active material mixture layer, the active material mixture layer is formed on the surface of the current collector. For the positive electrode.

The positive electrode active material has a protective coating having a pH of less than 11.5 when mixed with water. When the positive electrode active material is mixed with water to have a pH of less than 11.5, the reaction between the active material paste and the positive electrode current collector can be suppressed when the active material paste is prepared. By suppressing the reaction between the active material paste and the positive electrode current collector, the progress of corrosion of aluminum can be suppressed. Therefore, generation of hydrogen gas on the surface of the current collector is suppressed, and a positive electrode for a lithium battery having a uniform active material mixture layer can be manufactured.

When the pH is 11.5 or higher, the reaction between the active material paste and the positive electrode current collector cannot be suppressed when the active material paste is prepared.

Here, the reactivity between pH and Al is determined as follows:
Al was immersed in an aqueous solution of 2.0, 11.8, 11.5, 11.3, 11.1, and evaluation was performed by the time until bubbles were generated on the Al surface. In this evaluation, Al
The aqueous solution in which was immersed was prepared by dissolving LiOH.H ₂ O in water, and the pH was adjusted by adjusting the amount of dissolution. Al immersed in the aqueous solution is 1N30-H.
Material (Al: 99.3% or more) was used.

In this evaluation, the measured bubble generation time was within 1 minute when the pH was 11.5 or higher.
In the example of pH 11.3, it was 4 minutes. From this, when the pH is less than 11.5, the reaction between the current collector and the active material paste is suppressed, and a uniform active material mixture layer is formed.

The pH of the active material paste is preferably maintained below 11.5. The pH of the active material paste is 1
By maintaining the ratio below 1.5, the reaction between the current collector and the active material paste is suppressed, and a uniform active material mixture layer is formed.

The protective film is preferably made of a hydrophobic material. Since the protective film is made of a hydrophobic material,
In the active material paste, the reaction between the positive electrode active material and water can be suppressed, and the pH can be prevented from increasing due to the elution of lithium.

The protective coating preferably does not interfere with the migration of lithium ions when the battery is assembled. That is, if the protective film formed on the surface of the positive electrode active material inhibits the movement of lithium ions, the electrode reaction in the positive electrode active material does not occur. An example of such a protective film is a protective film having pores through which lithium ions can pass.

The protective coating preferably contains carbon. Since carbon does not react with water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Further, as can be seen from the fact that carbon is introduced as a conductive agent in the active material mixture layer in an ordinary lithium battery, not only does it not decompose at the battery potential, but also the current collector and the positive electrode active material. Has the property of helping the electrical conduction of. Therefore, it becomes a stable protective film.

The protective coating preferably comprises polytetrafluoroethylene (PTFE). Since PTFE has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Also, PT
FE is stable in the working potential range of the electrode,
Does not decompose when using batteries. Therefore, deterioration of the active material mixture layer can be suppressed. Further, since PTFE is not easily dissolved in the electrolytic solution, deterioration of the electrode due to the protective film being dissolved in the electrolytic solution when the battery is formed can be suppressed. As can be seen from the fact that this PTFE is introduced as a binder that binds the positive electrode active material to the active material mixture layer in an ordinary lithium battery, it does not interfere with the electrode reaction of the positive electrode active material, It also functions as a glue.

The protective coating preferably has a conductive polymer. Since the conductive polymer has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. As this conductive polymer,
For example, polyaniline can be mentioned.

In the method for producing a positive electrode for a lithium battery of the present invention, the method for forming the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the method for producing a positive electrode for a lithium battery of the present invention is characterized by using a positive electrode active material having a protective coating, and the method for forming the protective coating is not limited. As the method for forming the protective film, for example, a method in which a positive electrode active material and a material forming the protective film are dispersed or dissolved in a solution to perform coating, and a solid phase reaction occurs between the positive electrode active material and the material forming the protective film. Examples thereof include a coating method and a method of depositing a material for forming a protective film on the positive electrode active material.

The protective coating is preferably formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective coating. That is, by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film, the protective film can be formed by a solid phase reaction. That is, since the protective film can be formed without using a solvent, increase in cost required for materials and manufacturing can be suppressed.

In the method for producing a positive electrode for a lithium battery of the present invention, the thickness of the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the characteristics of the protective coating itself differ depending on the material used, and thus the thickness required for inhibiting the reaction with water differs.

The method for producing the positive electrode for a lithium battery of the present invention is not particularly limited except that the surface of the positive electrode active material has a protective coating. That is, as a material forming the active material paste, a material used for manufacturing a conventional positive electrode for a lithium battery can be used.

The positive electrode active material LiMexOy (Me; N
i, Co, transition metal containing at least one of Mn, x,
y; arbitrary) is not particularly limited. For example, LiMnO ₂ , LiMn ₂ O ₄ , LiCoO ₂ , LiN
A compound in which various metal elements are substituted with iO ₂ as a main skeleton can be used.

LiMn ₂ O ₄ system, LiCoO ₂ system, Li
A NiO ₂ -based positive electrode active material is more preferable. That is, since it has excellent performance as a positive electrode active material such as excellent diffusion performance of electrons and lithium ions, a lithium battery having high charge / discharge efficiency and good cycle characteristics can be obtained.

For example, the reactivity of the positive electrode active material with water is
The order is LiNiO ₂ system> LiCoO ₂ system> LiMn ₂ O ₄ system, and the production method of the present invention exerts a particularly large effect when a LiNiO ₂ system positive electrode active material is used.

The active material paste preferably contains a binder and / or a conductive agent. When the active material paste has the binder and / or the conductive agent, the characteristics of the manufactured positive electrode are improved.

The binder has a function of binding the positive electrode active material particles. As the binder, a water-soluble polymer or emulsion can be used, and for example, carboxymethyl cellulose (CMC), methyl cellulose, polyethylene oxide, hydroxyethyl cellulose can be used alone or in combination.

The conductive agent ensures the electric conductivity of the positive electrode.
Examples of the conductive agent include one or a mixture of two or more carbon substances such as carbon black, acetylene black, and graphite.

In the method for producing a positive electrode for a lithium battery of the present invention, the positive electrode active material has a protective coating having a pH of 11.5 or less when mixed with water, so that the p of the active material paste is reduced.
Since H is 11.5 or less, corrosion of the current collector due to the active material paste is suppressed. As a result, the positive electrode for a lithium battery manufactured by the manufacturing method of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode manufactured using the manufacturing method of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

(Lithium Battery Positive Electrode) The lithium battery positive electrode of the present invention is made of LiMexOy (Me; Ni, Co, M).
a step of preparing an active material paste having a positive electrode active material composed of a transition metal containing at least one kind of n, x, y; any), and water; and the active material paste on the surface of a current collector composed of Al. A positive electrode active material for a lithium battery, which is subjected to a method for producing a positive electrode for a lithium battery having a step of applying and drying to form an active material mixture layer, wherein the positive electrode active material is: It has a protective coating with a pH below 11.5.

LiMexOy (Me; Ni, Co, Mn
In the step of preparing an active material paste having a positive electrode active material made of a transition metal containing at least one of x, y; and arbitrary) and water, an active material paste using water as a solvent is prepared.

By the step of applying the active material paste on the surface of the current collector made of Al and drying it to form the active material mixture layer, the active material mixture layer is formed on the surface of the current collector. For the positive electrode.

The positive electrode active material has a protective film having a pH of less than 11.5 when mixed with water. When the pH is 11.5 or less when mixed with water, the reaction between the active material paste and the positive electrode current collector is suppressed when the active material paste is prepared. By suppressing the reaction between the active material paste and the positive electrode current collector, the progress of corrosion of aluminum can be suppressed. Therefore, generation of hydrogen gas on the surface of the current collector is suppressed, and a positive electrode for a lithium battery having a uniform active material mixture layer can be manufactured.

When the pH is 11.5 or higher, the reaction between the active material paste and the positive electrode current collector cannot be suppressed when the active material paste is prepared.

Here, the reactivity between pH and Al is determined as follows:
Al was immersed in an aqueous solution of 2.0, 11.8, 11.5, 11.3, 11.1, and evaluation was performed by the time until bubbles were generated on the Al surface. In this evaluation, Al
The aqueous solution in which was immersed was prepared by dissolving LiOH.H ₂ O in water, and the pH was adjusted by adjusting the amount of dissolution. Al immersed in the aqueous solution is 1N30-H.
Material (Al: 99.3% or more) was used.

In this evaluation, the measured bubble generation time was within 1 minute when the pH was 11.5 or higher.
In the example of pH 11.3, it was 4 minutes. From this, when the pH is less than 11.5, the reaction between the current collector and the active material paste is suppressed, and a uniform active material mixture layer is formed.

The pH of the active material paste is preferably maintained below 11.5. The pH of the active material paste is 1
By maintaining the ratio below 1.5, the reaction between the current collector and the active material paste is suppressed, and a uniform active material mixture layer is formed.

The protective film is preferably made of a hydrophobic material. Since the protective film is made of a hydrophobic material,
In the active material paste, the reaction between the positive electrode active material and water can be suppressed, and the pH can be prevented from increasing due to the elution of lithium.

The protective coating preferably does not interfere with the migration of lithium ions when the battery is assembled. That is, if the protective film formed on the surface of the positive electrode active material inhibits the movement of lithium ions, the electrode reaction in the positive electrode active material does not occur. An example of such a protective film is a protective film having pores through which lithium ions can pass.

The protective coating preferably contains carbon. Since carbon does not react with water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Further, as can be seen from the fact that carbon is introduced as a conductive agent in the active material mixture layer in an ordinary lithium battery, not only does it not decompose at the battery potential, but also the current collector and the positive electrode active material. Has the property of helping the electrical conduction of. Therefore, it becomes a stable protective film.

The protective coating preferably comprises polytetrafluoroethylene (PTFE). Since PTFE has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. Also, PT
FE is stable in the working potential range of the electrode,
Does not decompose when using batteries. Therefore, deterioration of the active material mixture layer can be suppressed. Further, since PTFE is difficult to dissolve in the electrolytic solution, the deterioration of the electrode due to the protective film being dissolved in the electrolytic solution when the battery is formed can be suppressed. As can be seen from the fact that this PTFE is introduced as a binder that binds the positive electrode active material to the active material mixture layer in an ordinary lithium battery, it does not interfere with the electrode reaction of the positive electrode active material. It also functions as a glue.

The protective coating preferably contains a conductive polymer. Since the conductive polymer has a small amount of dissolution in water, the reaction between the positive electrode active material and water is suppressed when the active material paste is formed. As this conductive polymer,
For example, polyaniline can be mentioned.

In the lithium battery positive electrode of the present invention, the method for forming the protective coating on the surface of the positive electrode active material is not particularly limited. That is, the positive electrode for a lithium battery of the present invention is characterized by using a positive electrode active material having a protective coating, and the method for forming the protective coating is not limited. Examples of the method for forming the protective film include a method in which the positive electrode active material and the material forming the protective film are dispersed or dissolved in a solution to perform coating, and a solid phase reaction occurs between the positive electrode active material and the material forming the protective film. Examples thereof include a coating method and a method of depositing a material for forming a protective film on the positive electrode active material.

The protective coating is preferably formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective coating. That is, by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film, the protective film can be formed by a solid phase reaction. That is, since the protective film can be formed without using a solvent, increase in cost required for materials and manufacturing can be suppressed.

In the method for producing a positive electrode for a lithium battery of the present invention, the thickness of the protective film on the surface of the positive electrode active material is not particularly limited. That is, the characteristics of the protective coating itself differ depending on the material used, and thus the thickness required for inhibiting the reaction with water differs.

The positive electrode for a lithium battery of the present invention is not particularly limited, except that it has a protective coating on the surface of the positive electrode active material. That is, as a material forming the active material paste, a material used for manufacturing a conventional positive electrode for a lithium battery can be used.

The positive electrode active material LiMexOy (Me; N
i, Co, transition metal containing at least one of Mn, x,
y; arbitrary) is not particularly limited. For example, LiMnO ₂ , LiMn ₂ O ₄ , LiCoO ₂ , LiN
A compound in which various metal elements are substituted with iO ₂ as a main skeleton can be used.

LiMn ₂ O ₄ system, LiCoO ₂ system, Li
A NiO ₂ -based positive electrode active material is more preferable. That is, since it has excellent performance as a positive electrode active material such as excellent diffusion performance of electrons and lithium ions, a lithium battery having high charge / discharge efficiency and good cycle characteristics can be obtained.

For example, the reactivity of the positive electrode active material with water is
The order is LiNiO ₂ system> LiCoO ₂ system> LiMn ₂ O ₄ system, and the production method of the present invention exerts a particularly large effect when a LiNiO ₂ system positive electrode active material is used.

The active material paste preferably contains a binder and / or a conductive agent. When the active material paste has the binder and / or the conductive agent, the characteristics of the manufactured positive electrode are improved.

The binder has a function of binding the particles of the positive electrode active material. As the binder, a water-soluble polymer or emulsion can be used, and for example, carboxymethyl cellulose (CMC), methyl cellulose, polyethylene oxide, hydroxyethyl cellulose can be used alone or in combination.

The conductive agent ensures the electric conductivity of the positive electrode.
Examples of the conductive agent include one or a mixture of two or more carbon substances such as carbon black, acetylene black, and graphite.

In the positive electrode for a lithium battery of the present invention, when the active material paste is applied to the surface of the current collector, corrosion of the current collector by the active material paste is suppressed. As a result, the positive electrode for a lithium battery of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode for a lithium battery of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

(Lithium Battery) The positive electrode manufactured by the method for manufacturing a positive electrode for a lithium battery of the present invention and the positive electrode for a lithium battery of the present invention can form a lithium battery in the same manner as a normal positive electrode for a lithium battery. .

That is, it can be manufactured by accommodating the positive electrode and the negative electrode together with the electrolytic solution in the battery container.

The negative electrode is not particularly limited in material constitution as long as it can absorb lithium ions during charging and release lithium ions during discharging, and known materials can be used. In particular, it is preferable to use a mixture obtained by mixing the negative electrode active material and the binder and applying the mixture to the current collector.

The negative electrode active material is not particularly limited, and a known active material can be used. For example, carbon materials such as highly crystalline natural graphite and artificial graphite,
Examples thereof include metallic lithium, lithium alloys, metallic materials such as tin compounds, and conductive polymers.

The binder has a function of binding the active material particles. As the binder, an organic binder or an inorganic binder can be used. For example, polyvinylidene fluoride (PVDF), polyvinylidene chloride, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR) can be used. They can be used alone or in combination.

As the current collector of the negative electrode, for example, a net, punched metal, foam metal or a foil processed into a plate shape of copper, nickel or the like can be used.

The electrolytic solution may be any electrolytic solution used in ordinary lithium secondary batteries, and is composed of an electrolyte salt and a non-aqueous solvent.

Examples of the electrolyte salt include LiP
F₆, LiBF_Four, LiClO_Four, LiAsF₆, LiC
l, LiBr, LiCF₃SO₃, LiN (CF₃S
O₂)₂, LiC (CF₃SO₂)₃, LiI, LiAlC
l_Four, NaClO_Four, NaBF_Four, Nal, etc.
And especially LiPF₆, LiBF_Four, LiClO_Four,
LiAsF₆Inorganic lithium salts such as LiN (SO₂C_x
F_{2x + 1}) (SO₂C_yF_{2y + 1}) Organic lithium salt represented by
Can be raised. Where x and y are 1 to 4
It represents an integer, and x + y is 3 to 8. Organic richiu
Specifically, LiN (SO₂CF₃)
(SO₂C₂F_Five), LiN (SO₂CF₃) (SO₂C
₃F ₇), LiN (SO₂CF₃) (SO₂C_FourF₉), Li
N (SO₂C₂F_Five) (SO₂C ₂F_Five), LiN (SO₂C₂
F_Five) (SO₂C₃F₇), LiN (SO₂C₂F_Five) (SO₂
C_FourF₉) Etc. Among them, LiN (SO₂C
F₃) (SO₂C_FourF₉), LiN (SO₂C₂F_Five) (SO
₂C₂F_Five) Is used as the electrolyte, it has excellent electrical characteristics.
It is preferable because

The organic solvent in which the electrolyte salt is dissolved is not particularly limited as long as it is an organic solvent used for a non-aqueous electrolyte of a usual lithium secondary battery, and examples thereof include carbonate compounds, lactone compounds, ether compounds and sulfolane compounds. , Dioxolane compounds, ketone compounds, nitrile compounds, halogenated hydrocarbon compounds and the like. Specifically, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethylene glycol dimethyl carbonate, propylene glycol dimethyl carbonate, ethylene glycol diethyl carbonate, carbonates such as vinylene carbonate, lactones such as γ-butyl lactone, Ethers such as dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, sulfolanes such as sulfolane and 3-methylsulfolane, dioxolanes such as 1,3-dioxolane, 4-methyl-2- Ketones such as pentanone, acetonitrile,
Examples thereof include nitriles such as pyropionitrile, valeronitrile and benzonitrile, halogenated hydrocarbons such as 1,2-dichloroethane, and other methyl formate, dimethylformamide, diethylformamide, dimethyl sulfoxide and the like. Further, it may be a mixture thereof.

Of these organic solvents, one or more non-aqueous solvents selected from the group consisting of carbonates are
It is preferable because it has excellent solubility, dielectric constant and viscosity of the electrolyte.

The lithium battery formed by using the positive electrode is
The shape is not particularly limited, and it can be used as a battery of various shapes such as a sheet type, a coin type, a cylindrical type, and a square type. It is preferable that the positive electrode and the negative electrode are formed in a sheet shape, and the wound electrode body is wound with a sheet separator interposed therebetween. Furthermore, since it is excellent in volumetric efficiency, a flat wound electrode body is more preferable.

The separator is not particularly limited as long as it is a separator used for ordinary lithium secondary batteries, and examples thereof include a porous resin made of polyethylene, polypropylene or the like.

The lithium battery formed by using the positive electrode is
Since the cycle characteristics of the positive electrode are not deteriorated, the cycle characteristics are excellent.

[0140]

EXAMPLES The present invention will be described below with reference to examples.

As an example of the present invention, a positive electrode for a lithium battery was manufactured.

(Example) The positive electrode for a lithium battery of the example was manufactured by the following means.

First, LiNi _0.81 having an average particle size of about 7 μm was used.
85 parts by weight of Co _0.16 Al _0.03 O ₂ particles and carbon particles having an average particle size of about 0.03 μm (Ketjen Black
4 parts by weight of ECP-600JD) was put into a mechanofusion device (manufactured by Hosokawa Micron), and compressive stress and shear stress were applied to produce positive electrode active material particles coated with a carbon film. Here, the mechanofusion device was operated under the condition of applying compressive stress and shear stress for 90 minutes at a rotation speed of 1350 rpm.

When a cross section of the produced positive electrode active material coated with carbon was observed by Auger electron spectroscopy, the thickness of the carbon coating was 0.3 μm. The density of the carbon coating and the true density of the carbon particles (2.25 g /
When the void amount of the carbon coating was calculated from m ³ ),
It can be seen that the carbon coating has about 10% voids.

Further, the pH of the filtrate obtained by pouring the positive electrode active material having the carbon coating into pure water so that the ratio becomes 10 wt% when the whole amount is 100 wt%, holding it for 1 hour, and then filtering. Was 11.2.

Next, an active material paste was prepared. 91 wt% of the positive electrode active material having a carbon coating, 6 wt% of carbon black as a conductive agent, and 2 wt% of carboxymethyl cellulose (C as a binder that also functions as a thickener).
MC), PTFE dispersion of binder as PTFE
1 wt% in terms of conversion was put into pure water and kneaded using a homogenizer type kneader.

After that, the prepared active material paste was Al
It was applied to the surface of a current collector made of foil. Here, as the Al foil, an Al foil made of 1N30-H material (Al: 99.3% or more) and having a thickness of 15 μm was used. The Al foil had a thickness of 0.01 μm caused by oxygen in the atmosphere.
It has an oxide film of.

Application of the active material paste was carried out by using a comma coater on the surface of the Al foil at a basis weight of 7 (mg / cm ² ) per side.
It was applied on both sides. After that, it was dried by passing through the furnace maintained at 60 ° C. and 120 ° C. for 0.8 minutes respectively. At this time, no crack was observed in the obtained active material mixture layer, and the coating state was good.

Then, press molding was performed at a linear pressure of 2 (ton / cm) to improve the density of the active material mixture layer.

Comparative Example The positive electrode for a lithium battery of the comparative example was manufactured in the same manner as the positive electrode for a lithium battery of the example except that the carbon coating was not formed.

Specifically, the positive electrode active material has an average particle size of 7
_{LiNi 0.81 Co 0.16 Al 0. 03 O} 2 particles μm are used.

The total amount of the positive electrode active material particles was 100 wt.
%, When added to pure water at a rate of 10 wt%,
The pH of the filtrate obtained by filtering after holding for 1 hour is 1
It was 1.9.

Subsequently, an active material paste was prepared. 87% by weight of positive electrode active material, carbon black 10 of conductive agent
wt%, 2 wt% as a binder that also functions as a thickener
Carboxymethyl cellulose (CMC), P as a binder
1% by weight of TFE dispersion in terms of PTFE was put into pure water and kneaded using a homogenizer type kneader.

Then, as in the example, the active material paste was applied to the surface of the current collector made of Al foil and dried. In addition,
In the comparative example, when the drying time was 0.8 minutes, hydrogen gas was generated due to the reaction between the active material paste and the Al foil, and the active material mixture layer was cracked. Therefore, the drying time was set to 2.7 minutes. . Further, even after the drying time was 2.7 minutes, after the drying, press molding was performed at a linear pressure of 2 (ton / cm) to improve the density of the active material mixture layer.

The positive electrode for a lithium battery of Comparative Example was manufactured by the above means.

(Evaluation) As the evaluation of the positive electrodes of the examples and comparative examples, a lithium battery was manufactured and the cycle characteristics of this lithium battery were measured.

(Production of Lithium Battery) 98 wt% graphite as a negative electrode active material, 1 wt% carboxymethyl cellulose (CMC) as a binder, and 1 styrene-butadiene rubber (SBR) dispersion in terms of SBR.
wt% was put into pure water and kneaded using a homogenizer type kneader to prepare a negative electrode active material paste.

The prepared negative electrode active material paste was coated on a copper foil with a comma coater in the same manner as the positive electrode so that the basis weight per surface was 4 (mg / cm ² ) and the paste was dried. After that, a linear pressure of 1.0 (ton / cm) is applied through a roll press machine so that the electrode density is 1.
An electrode having an elevated temperature of 25 (g / cm ² ) was produced.

The negative electrode was manufactured by the above means.

The negative electrode obtained above and the positive electrodes of Examples and Comparative Examples were wound with a separator interposed therebetween to form a wound electrode, and this electrode was inserted into the case.
At this time, the current collecting lead was joined to the positive electrode terminal and the negative electrode terminal of the case.

The separator is a polyethylene porous film having a thickness of 25 μm, and the electrolytic solution contains ethylene carbonate (EC) and diethylene carbonate (DEC).
1mo as an electrolyte in a solvent mixed in a volume ratio of 0:70
It was used by dissolving LiPF ₆ in l / l.

The case in which the wound electrode is housed is
It had an internal space with a diameter of 18 mm and a height of 65 mm.

After that, the electrolytic solution was injected into the case, and the case was closed.

(Cycle characteristics) The cycle characteristics are measured by
It was carried out by the following means.

First, after charging at a room temperature up to the fifth cycle at a current of 1 C, a constant voltage of 4.1 V for 2.5 hours, a constant current and a constant voltage of 2.5 hours were applied, and then discharge was performed at a final voltage of 3 V with a current of 1/3 C. went. After each charge and discharge, a no-load period of 10 minutes was provided. The capacity of the battery at the 5th cycle was used as the initial capacity.

Subsequently, the battery was kept in a constant temperature bath at 60 ° C. and subjected to constant current charging (current: 2 C, voltage: 4.1 V) and constant current discharging (current: 2 C, voltage: up to 3 V) for 500 cycles. It was charged and discharged.

Table 1 shows the measurement results of the initial capacities and the capacities after 500 cycles of the batteries of Examples and Comparative Examples.

[0168]

[Table 1]

From Table 1, the batteries of Examples had an initial capacity of 15
High as 7 mAh / g and capacity after 500 cycles is 1
The efficiency was maintained at 32 mAh / g and 84%. On the other hand, the battery of the comparative example has an initial capacity of 145 mAh / g,
The capacity after 500 cycles was 110 mAh / g, which is lower than any of the batteries of the examples.

From this, it is understood that by forming the carbon coating on the surface of the positive electrode active material, the initial capacity of the battery and the capacity after cycle characteristics are improved.

[0171]

In the positive electrode for a lithium battery manufactured by the manufacturing method of the present invention, corrosion of the current collector due to the active material paste is suppressed when the active material paste is applied to the surface of the current collector. As a result, the positive electrode of the present invention becomes an electrode in which the positive electrode active material is uniformly dispersed. The positive electrode for a lithium battery of the present invention exhibits an effect of exhibiting high battery characteristics when a lithium battery is formed.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Manabu Yamada             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO (72) Inventor Kenichiro Kami             1-1, Showa-cho, Kariya city, Aichi stock market             Inside the company DENSO F term (reference) 5H029 AJ13 AJ14 AK03 CJ11 CJ21                       DJ11 EJ04 EJ12 EJ13                 5H050 AA18 AA19 BA15 CA07 DA02                       DA08 EA00 HA02

Claims (20)

[Claims] 1. LiMexOy (Me; Ni, Co, M
a step of preparing an active material paste having a positive electrode active material composed of a transition metal containing at least one of n, x and y; any), and water; and the active material paste on the surface of a current collector composed of Al. And a step of forming an active material mixture layer by drying the positive electrode active material, wherein the positive electrode active material is a protective film that suppresses reaction with water and has electrical conductivity. A method for producing a positive electrode for a lithium battery, comprising: 2. The method for manufacturing a positive electrode for a lithium battery according to claim 1, wherein the protective film contains carbon. 3. The method for producing a positive electrode for a lithium battery according to claim 1, wherein the protective film contains polytetrafluoroethylene (PTFE). 4. The method for producing a positive electrode for a lithium battery according to claim 1, wherein the protective coating contains a conductive polymer. 5. The method for producing a positive electrode for a lithium battery according to claim 1, wherein the protective film is formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film. 6. LiMexOy (Me; Ni, Co, M
a step of preparing an active material paste having a positive electrode active material composed of a transition metal containing at least one of n, x and y; any), and water; and the active material paste on the surface of a current collector composed of Al. Is applied and dried to form an active material mixture layer, the positive electrode for a lithium battery being subjected to a method for producing a positive electrode for a lithium battery, wherein the positive electrode active material comprises a reaction with water. A positive electrode for a lithium battery, characterized in that it has a protective coating that suppresses the above and has electrical conductivity on the surface. 7. The positive electrode for a lithium battery according to claim 6, wherein the protective film contains carbon. 8. The positive electrode for a lithium battery according to claim 6, wherein the protective film is made of PTFE. 9. The positive electrode for a lithium battery according to claim 6, wherein the protective film is made of a conductive polymer. 10. The positive electrode for a lithium battery according to claim 6, wherein the protective film is formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film. 11. LiMexOy (Me; Ni, Co,
Transition metal containing at least one Mn, x, y; optional)
And a step of preparing an active material paste containing water, and a step of applying the active material paste to the surface of a current collector made of Al and drying the active material mixture layer to form an active material mixture layer. The method for producing a positive electrode for a lithium battery, comprising: a positive electrode active material having a protective coating having a pH of less than 11.5 when mixed with water. 12. The method for manufacturing a positive electrode for a lithium battery according to claim 5, wherein the protective film contains carbon. 13. The method for manufacturing a positive electrode for a lithium battery according to claim 5, wherein the protective coating is made of PTFE. 14. The method for producing a positive electrode for a lithium battery according to claim 5, wherein the protective coating is made of a conductive polymer. 15. The method for producing a positive electrode for a lithium battery according to claim 1, wherein the protective film is formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film. 16. LiMexOy (Me; Ni, Co,
Transition metal containing at least one Mn, x, y; optional)
And a step of preparing an active material paste containing water, and a step of applying the active material paste to the surface of a current collector made of Al and drying the active material mixture layer to form an active material mixture layer. And a positive electrode active material having a protective coating having a pH of less than 11.5 when mixed with water. Characteristic positive electrode for lithium batteries. 17. The positive electrode for a lithium battery according to claim 16, wherein the protective film contains carbon. 18. The positive electrode for a lithium battery according to claim 16, wherein the protective film is made of PTFE. 19. The positive electrode for a lithium battery according to claim 16, wherein the protective coating is made of a conductive polymer. 20. The positive electrode for a lithium battery according to claim 16, wherein the protective film is formed by applying compressive stress and / or shear stress to the positive electrode active material and the material forming the protective film.