JPH10302780A - Manufacture of lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent cracks of a sheet positive electrode or separation of a coating film from a conductive substrate by manufacturing the sheet positive electrode through the processes where a coating material prepared by adding at least an organic solvent to mixed powder containing polytetrafluoroethylene and agitating and mixing in a wet condition, is applied to the conductive substrate and dried. SOLUTION: A resin, rubber, organic solvent or the like are added to mixed powder containing polytetrafluoroethylene, and then agitated and mixed, to prepare a coating material having each component highly dispersed. The coating material is applied to a conductive substrate, and dried to prepare a sheet type positive electrode film. The polytetrafluoroethylene in the electrode film effectively acts to keep the large bonding strength of each component in the film and the bonding strength of the film to the conductive substrate. Therefore even when a stacked electrode is bent to a circular arc from, the occurrence of a crack on the film or the separation thereof from the conductive substrate is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a lithium secondary battery, and more particularly, to a method of manufacturing a lithium secondary battery having a sheet-like positive electrode having a large adhesive strength.

[0002]

2. Description of the Related Art In general, a coating prepared by adding a binder or a solvent to a positive electrode active material, dispersing and stirring, is applied on a conductive substrate, and dried to form a coating film containing the positive electrode active material. In the same manner as the sheet-shaped positive electrode produced by the above, a binder or a solvent is added to the negative electrode active material, and dispersed,
A coating prepared by stirring is applied on a conductive substrate, and the laminated electrode body in which a sheet-shaped negative electrode having a coating film containing a negative electrode active material and the like is dried and opposed to each other via a separator is formed into a spiral shape. After being bent into an arc shape and formed into a cylindrical or rectangular parallelepiped shape, the lithium secondary battery produced by encapsulating it in a battery case together with an organic solvent-based electrolyte has an energy density per unit capacity and a unit weight per unit weight. Has a high energy density.

[0003] The binder used for the sheet-like electrodes such as the above-mentioned sheet-like positive electrode and sheet-like negative electrode has resistance to strong oxidizing action by an active material at the time of charging and chemical stability to an organic solvent-based electrolyte. From the requirements, it is considered that a fluororesin, particularly polytetrafluoroethylene, is suitable.

[0004] The form of the polytetrafluoroethylene generally includes an aqueous dispersion and a fine powder. The aqueous dispersion of the former is an aqueous dispersion of tetrafluoroethylene produced by emulsion polymerization in water using tetrafluoroethylene monomer as a raw material,
Further, an aqueous dispersion of polytetrafluoroethylene prepared by adding a surfactant or the like, and the latter fine powder is a polytetrafluoroethylene obtained by coagulating the aqueous dispersion of polytetrafluoroethylene. It is a fine powder of tetrafluoroethylene.

[0005] Among these two kinds of polytetrafluoroethylene, an aqueous dispersion of polytetrafluoroethylene is mainly used as a binder for an electrode. This aqueous dispersion of polytetrafluoroethylene is a highly dispersed liquid in which polytetrafluoroethylene particles having an average particle size of about 0.1 to 0.5 μm are dispersed in water, and may be mixed with an active material, an electron conduction aid, and the like. Therefore, it is possible to obtain a coating material in which each material is uniformly dispersed.

[0006]

However, when the above aqueous dispersion of polytetrafluoroethylene is mixed with an active material to prepare a coating, the viscosity of the coating does not have thixotropy and the flowability is poor. Therefore, it is difficult to efficiently form a coating film on the conductive substrate. Particularly, in the case of the positive electrode, the adhesion between the coating film formed by applying the above coating material on the conductive substrate and drying and the conductive substrate is low. Since the coating film is weak and the coating film easily peels off from the conductive substrate, it is not possible to form a cylindrical or rectangular parallelepiped molded body by bending the film into the above-described arc shape.

Therefore, when producing a sheet-like electrode using an aqueous dispersion of polytetrafluoroethylene as a binder, Japanese Patent Application Laid-Open No. 2-158055 discloses that a powdery active material and an electron conduction aid are mixed. Then, an aqueous solution of carboxymethylcellulose is added as a viscous agent to the mixture and kneaded, and then a dispersion of polytetrafluoroethylene is added and kneaded to prepare a paint, and the paint is formed into a film-shaped conductive material such as a rolled aluminum foil. It has been reported that a coating film having excellent adhesion strength to a conductive substrate could be obtained by applying the composition on a conductive substrate and drying. JP-A-4-267054 discloses that polytetrafluoroethylene and a polymerization degree of 100 are used.
A method using a combination of polyvinyl alcohol having a saponification degree of 0 to 1700 and a degree of saponification of 93 to 96 mol% has been proposed.

Further, in the above publication, besides the above-mentioned carboxymethylcellulose and polyvinyl alcohol, cellulose resins such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose, and sodium polyacrylate can be used as the viscosity agent. It is described.

However, since the paint prepared by adding the above-mentioned viscous agent uses water as a solvent, lithium elutes from the positive electrode active material and reacts with water, thereby deteriorating the positive electrode active material. There was a problem that occurs. This phenomenon is more likely to occur when a positive electrode active material that provides a high capacity is used. For example, when lithium nickel oxide is used as the positive electrode active material, there is a problem that the battery capacity is reduced to 1/10 or less. there were. In addition, even with a paint in which a viscous agent was dissolved in alcohol and added, deterioration of the positive electrode active material could not be completely prevented.

On the other hand, polytetrafluoroethylene fine powder can use an organic solvent in addition to water and alcohol as a solvent for preparing a coating material, and furthermore, a surfactant or the like which causes deterioration of battery characteristics. Therefore, it is possible to prevent lithium in the positive electrode active material from being eluted into water or alcohol and reacting with water or alcohol to lower the battery characteristics.
In addition, the use of fine powder of polytetrafluoroethylene makes it possible to use low-boiling organic solvents such as ketones and toluene, which have poor compatibility with water. Will be possible.

However, when a paint is prepared using this polytetrafluoroethylene fine powder, a dispersion of an organic solvent of polytetrafluoroethylene is required in place of the dispersion of polytetrafluoroethylene.

In order to obtain such a dispersion of polytetrafluoroethylene in an organic solvent, the fine powder of polytetrafluoroethylene is vigorously stirred to highly disperse it in an appropriate organic solvent. Are rubbed and fibril fibers are entangled. Since such a dispersion in which polytetrafluoroethylene is converted into fibril fibers is a gum-like solid solution having poor fluidity, it is impossible to prepare a coating material using the same.

On the other hand, in order to prevent fibril fiber formation,
If the stirring is weak, there is a problem that the secondary particles of the polytetrafluoroethylene fine powder cannot be completely dispersed to the primary particles. And when a sheet-like electrode is produced using a dispersion of polytetrafluoroethylene in which the secondary particles of such fine powder of polytetrafluoroethylene remain, since there is little polytetrafluoroethylene acting as a binder, There is a problem that the adhesive strength between the coating film and the conductive substrate is reduced.

Also, in a method in which fine powder of polytetrafluoroethylene, an active material, a viscous agent, and the like are charged into a stirring vessel and a coating is prepared by stirring, the particles of the polytetrafluoroethylene are rubbed with each other when strongly stirring. It becomes fibril fibril and becomes a gum-like solid solution with poor fluidity, making it impossible to apply. On the other hand, if agitated weakly to prevent fibril fiberization, secondary particles of fine powder of polytetrafluoroethylene remain in the paint, and the paint was applied on a conductive substrate and dried to prepare a sheet. In the shape of the electrode, there is a problem that the adhesive strength of the coating film is low.

In order to increase the battery capacity as much as possible within a limited battery volume, the above-mentioned laminated electrode body is bent into an arc shape and formed into a cylindrical or rectangular parallelepiped shape. If it is attempted to reduce the size, there is a problem that cracks occur in the coating film or the coating film peels off from the conductive substrate in the case of a sheet-like electrode having a low adhesion strength of the coating film as described above.

Accordingly, the present invention uses a fine powder of polytetrafluoroethylene as a binder to reduce the adhesive strength of a coating film of a sheet-shaped positive electrode, particularly in which cracking of the coating film and peeling of the coating film from the conductive substrate are likely to occur. An object of the present invention is to provide a high-capacity lithium secondary battery by preventing the occurrence of cracks in the coating film of the sheet-shaped positive electrode and peeling of the coating film from the conductive substrate.

[0017]

Means for Solving the Problems The present invention has been made as a result of conducting various studies to solve the above problems.
A sheet-shaped positive electrode on which a coating containing at least a positive electrode active material and a binder is formed on a conductive substrate, wherein the binder of the sheet-shaped positive electrode includes at least polytetrafluoroethylene and a resin or rubber soluble in an organic solvent. In the production of a lithium secondary battery containing polytetrafluoroethylene, at least the positive electrode active material is added in advance to fine powder of polytetrafluoroethylene, and the mixture is stirred and mixed in a dry manner to prepare a polytetrafluoroethylene-containing mixture powder. The above-mentioned problem is caused by preparing a sheet-shaped positive electrode through a process of adding at least an organic solvent to the mixture powder, stirring and mixing in a wet manner, and coating the prepared coating material on a conductive substrate, and drying and forming a coating film. Is solved.

That is, the polytetrafluoroethylene-containing mixture powder in the present invention is prepared by adding at least the positive electrode active material to polytetrafluoroethylene fine powder and mixing and stirring in a dry system. Since the powder particles such as the positive electrode active material are interposed between the polytetrafluoroethylene particles, it is possible to prevent the particles of the polytetrafluoroethylene from sliding with each other to form fibril fibers and to be entangled. Moreover, since the solid particles such as the positive electrode active material are simultaneously mixed while dissolving the secondary particles of polytetrafluoroethylene into the primary particles,
A polytetrafluoroethylene-containing mixture powder in which each material particle is highly dispersed is obtained.

Further, a resin or rubber, an organic solvent, or the like is added to the polytetrafluoroethylene-containing powder mixture and mixed with stirring to obtain a coating material in which each material is highly dispersed. The coating film of the sheet-shaped positive electrode, which was coated and dried on the top, was treated with polytetrafluoroethylene effectively, so the adhesive strength between the positive electrode materials in the coating film and the coating film on the conductive substrate The adhesive strength is high, and therefore, even when the laminated electrode body is bent into an arc shape and formed into a cylindrical or rectangular parallelepiped shape, cracks are generated in the coating film and the coating film does not peel off from the conductive substrate. Is prevented.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a fine powder of polytetrafluoroethylene having an average particle diameter of about 0.1 to 0.5 .mu.
What formed the secondary particle of about 0 micrometer or less is preferable.

Examples of the resin soluble in polytetrafluoroethylene and the organic solvent constituting the binder include polyvinyl butyral, polyethylene glycol, and the like.
Hydroxypropyl cellulose, polyvinylidene fluoride and the like can be used. Further, as the rubber, for example, ethylene-propylene-diene rubber or the like can be used. These resins or rubbers may be used alone or in combination of two or more. Furthermore, you may use together with another resin or rubber. The resin or rubber soluble in the organic solvent may be dissolved in the organic solvent in advance, or may be added to the polytetrafluoroethylene-containing powder mixture and mixed with the organic solvent at the time of preparing the coating material, or may be mixed with the polytetrafluoroethylene. When the ethylene-containing mixture powder is prepared, it may be mixed with polytetrafluoroethylene or the like.

In the present invention, the mixing ratio of the polytetrafluoroethylene to the resin or rubber soluble in the organic solvent is 5 to 95% by weight, especially 10 to 90% by weight of the polytetrafluoroethylene. It is preferable that the resin or rubber soluble in water is 5 to 95% by weight, particularly 10 to 90% by weight. Further, the content of the binder in the coating film of the sheet-shaped positive electrode is 0.2 to 20% by weight,
In particular, the content is preferably 0.5 to 10% by weight.

The solvent used in preparing the paint may be any organic solvent that dissolves the resin or rubber constituting the binder, and the organic solvent may be appropriately selected and employed according to the type of the resin or rubber. Preferably, for example, when the resin is polyvinyl butyral or polyethylene glycol, a mixed solvent of cyclohexanone and toluene is suitable, when the resin is hydroxypropyl cellulose, dioxane is suitable, and when the resin is polyvinylidene fluoride, Is preferably N-methylpyrrolidone, and when the rubber is ethylene-propylene-diene rubber, toluene is suitable. However, these are merely examples, and the present invention is not limited thereto.

In the present invention, for preparing the polytetrafluoroethylene-containing mixture powder by stirring under dry conditions, for example, a kneader or a planetary mixer can be used as the stirring mixer. Further, in preparing the coating material, as a stirring mixer for adding an organic solvent and the like to the polytetrafluoroethylene-containing mixture powder and stirring and mixing in a wet manner, for example, a ball mill, a sand grind mill, a homogenizer mixer, or the like is used. be able to.

In the present invention, as the positive electrode active material, lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide (these are usually Li
LiO, such as NiO ₂ , LiCoO ₂ , and LiMn ₂ O ₄ , wherein the ratio of Li to Ni, the ratio of Li to Co, and the ratio of Li to Mn often deviate from the stoichiometric composition. The contained composite metal oxide is used alone or as a mixture of two or more thereof, or as a solid solution thereof. In the present invention, deterioration can be prevented even when a lithium nickel oxide, which can be expected to have a high capacity, is used, so that a high-capacity lithium secondary battery can be obtained. In preparing the positive electrode, an electron conduction aid such as flaky graphite, acetylene black, and carbon black can be added to the positive electrode active material as needed.

The positive electrode contains, for example, the above-mentioned positive electrode active material, the above-mentioned electron conduction aid as required, and the above-mentioned polytetrafluoroethylene fine powder or a resin or rubber soluble in an organic solvent as a binder. The coating is prepared by applying a coating prepared in a specific embodiment on a conductive substrate, drying the coating, and forming a coating film containing at least a positive electrode active material and a binder on the conductive substrate. In the present invention, to form a coating film on the conductive substrate,
This includes not only the case where a coating film is formed on one surface of the conductive substrate but also the case where a coating film is formed on both surfaces of the conductive substrate.

In the present invention, for example, lithium metal or a lithium-containing compound is used as the negative electrode active material, and the lithium-containing compound includes a lithium alloy and other compounds. Examples of the lithium alloy include lithium-aluminum and lithium-
Examples include alloys of lithium and other metals such as iron, lithium-bismuth, lithium-indium, lithium-gallium, and lithium-indium-gallium. Examples of the lithium-containing compound other than the lithium alloy include carbon fiber and graphite having a turbostratic structure. Some of these do not contain lithium at the time of manufacture,
When acting as a negative electrode active material, lithium is contained by chemical means and electrochemical means.

For the negative electrode, for example, an electron conduction aid such as flake graphite, acetylene black, carbon black or the like is added to the negative electrode active material, if necessary, and further, for example, polyvinylidene fluoride, polytetrafluoro A binder such as ethylene and ethylene-propylene-diene rubber is added, a solvent is further added, and a paint is prepared by mixing. The paint is applied to a conductive substrate, dried, and formed through a process of forming a coating film. You. However,
The method for manufacturing the negative electrode is not limited to the above method, and another method may be adopted. In preparing the negative electrode, the paint may be prepared by the same method as in the case of the positive electrode.

In the present invention, as a method of applying the above-mentioned coating material to the conductive substrate, various coating methods such as an extrusion coater, a reverse roller, a doctor blade, an applicator and the like can be used.

In the present invention, as a conductive substrate of a sheet-like electrode such as a sheet-like positive electrode and a sheet-like negative electrode, for example, a metallic conductive material such as aluminum, stainless steel, titanium, copper, etc. Metal or foil processed into a thin plate shape is used.

Examples of the electrolyte include 1,2-dimethoxyethane, 1,2-diethoxyethane, propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, diethyl carbonate, dimethyl carbonate, ethyl In a single solvent such as methyl carbonate or a mixed solvent of two or more, for example, LiCF ₃ SO ₃ , LiC ₄ F ₉ S
An organic solvent-based electrolyte prepared by dissolving an electrolyte such as O ₃ , LiClO ₄ , LiPF ₆ , or LiBF ₄ alone or in combination of two or more is used.

As the separator, for example, a thickness of 10
A microporous polyethylene film or a microporous polypropylene film having a porosity of 30 to 70% and a pore size of ５０50 μm is preferably used.

The battery is formed, for example, by bending a laminated electrode body in which a sheet-shaped positive electrode and a sheet-shaped negative electrode produced as described above are opposed to each other with a separator interposed therebetween, into a circular shape such as a spiral shape, or the like. After molding into a rectangular parallelepiped shape, the electrode body is inserted into a nickel-plated iron or stainless steel battery case, injected with an electrolyte, and sealed. Further, the battery usually incorporates an explosion-proof mechanism for discharging the gas generated inside the battery to the outside of the battery when the pressure has risen to a certain pressure, thereby preventing the battery from bursting under high pressure.

[0034]

Next, an embodiment of the present invention will be described.
However, the present invention is not limited to only these examples. In the examples below,% indicating the concentration and the like is% by weight.

Example 1 (1) Preparation of Positive Electrode The preparation of a positive electrode will be described in the order of synthesis of lithium nickel oxide used as a positive electrode active material, preparation of a paint, and formation of a coating film.

Synthesis of Lithium Nickel Oxide Lithium hydroxide (LiOH.H ₂ O) and nickel oxide (III) (Ni ₂ O ₃ ) were heat-treated to synthesize lithium nickel oxide. This synthesis was performed as follows.

Lithium hydroxide and nickel oxide are converted to Li /
After weighing so that Ni = 1 / 1.05 (molar ratio), it was mixed while pulverizing. This was preheated at 500 ° C. for 2 hours in an oxygen (O ₂ ) gas stream, and then heated to 700 ° C. at a heating rate of 50 ° C./h or less.
By heating at 0 ° C. for 20 hours and firing, lithium nickel oxide was synthesized. Since the synthesized lithium nickel oxide is weak against moisture, handling such as pulverization was performed in an argon gas atmosphere.

Preparation of Coating Film After the preparation of the polytetrafluoroethylene-containing mixture powder, the following ratios of lithium nickel oxide as the positive electrode active material, flaky graphite as the electron conduction aid, and polytetrafluoroethylene fine powder as the binder were used. A paint containing powder and the like was prepared. The average particle size of the primary particles of the used polytetrafluoroethylene fine powder was 0.1.
At 1 μm, the average particle size of the secondary particles was 6 μm.

Lithium nickel oxide 90 parts by weight Flake graphite 6 parts by weight Fine powder of polytetrafluoroethylene 3 parts by weight Polyvinyl butyral (average degree of polymerization 1800) 0.5 parts by weight Polyethylene glycol (average molecular weight 500000) 0.5 parts by weight Department

First, 90 parts by weight of lithium nickel oxide, 6 parts by weight of flaky graphite and 3 parts by weight of fine powder of polytetrafluoroethylene were added, and the mixture was mixed by dry stirring with a planetary mixer to obtain a polytetrafluoroethylene-containing mixture. Powder A was prepared. Separately, 0.5 parts by weight of polyvinyl butyral and 0.5 parts by weight of polyethylene glycol were dissolved in 9 parts by weight of a mixed solvent of cyclohexanone and toluene in a weight ratio of 1: 1 to prepare a resin solution having a concentration of 10%. .

The coating material was charged with the polytetrafluoroethylene-containing mixture powder A, the resin solution, and 31 parts by weight of a mixed solvent of cyclohexanone and toluene as an additional solvent in a weight ratio of 1: 1. It was prepared by wet stirring and mixing.

Formation of Coating Film The coating material obtained above was applied on an aluminum foil having a thickness of 20 μm using an applicator, and dried at 100 to 120 ° C. to form a coating film. Similarly, the above-mentioned paint was applied to the back surface side of the aluminum foil, and vacuum-dried at 100 ° C. for 8 hours to form a coating film. The thickness of the coating on one side of the electrode body after drying was 110 μm. Then, the electrode body was roll-pressed to produce a sheet-like positive electrode having a coating thickness on one side of 80 μm and a total thickness of 180 μm.

(2) Preparation of Negative Electrode A synthetic graphite (synthesized at 2800 ° C.) was used as the negative electrode active material, and polyvinylidene fluoride was used as the binder (however, it was previously dissolved in N-methylpyrrolidone and used as a 12% concentration solution). Was used to prepare paints containing them in the following proportions.

Artificial graphite (synthesized at 2800 ° C.) 90 parts by weight Polyvinylidene fluoride 10 parts by weight

The above-mentioned material for forming a negative electrode coating film was stirred and mixed to prepare a coating material for forming a negative electrode coating film, and the coating material was applied on a copper foil having a thickness of 18 μm using an applicator.
It was dried at 0 ° C. to form a coating film. Similarly, the above-mentioned paint was applied to the back side of the copper foil and dried to form a coating film, and then vacuum dried at 100 ° C. for 8 hours. The thickness of the coating on one side of the electrode body after drying was 110 μm. And
This electrode was roll-pressed and the coating thickness on one side was 80μ.
m, a sheet-shaped negative electrode having a total thickness of 178 μm was prepared. The coating density was adjusted so that the weight ratio of the active materials of the positive electrode and the negative electrode was 2: 1.

(3) Electrolyte An organic solvent-based electrolyte was prepared by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (mixing ratio was 1: 1 by volume).

(4) Assembly of Cylindrical Battery The sheet-shaped positive electrode was cut into a strip having a width of 28 mm and a length of 220 mm, and the sheet-shaped negative electrode was cut into a strip having a width of 30 mm and a length of 260 mm. Then, a part of the coating film of the sheet-shaped positive electrode was peeled off, and a lead made of aluminum was ultrasonically welded to a portion where the metal foil was exposed, and similarly, a part of the sheet-shaped negative electrode was peeled off to expose the metal foil. A lead member made of copper is resistance-welded to the portion thus formed, and a band-shaped separator made of a microporous polypropylene film having a thickness of 25 μm and a porosity of 50% is interposed between the sheet-shaped positive electrode and the sheet-shaped negative electrode. An electrode, and spirally winding it to produce a spiral electrode body,
The spiral electrode body was inserted into a battery case made of stainless steel. The minimum winding diameter of the sheet-shaped positive electrode of the spiral electrode body was 3.7 mm.

Then, the tip of the lead body on the negative electrode side is welded to the bottom of the battery case by penetrating the insulator, the insulator is inserted into the opening of the battery case, and a groove is formed. The plate and the lead body on the positive electrode side were welded. And
After vacuum-drying the can body in which the electrodes and the like manufactured through such a process are filled at 60 ° C. for 10 hours, 2 ml of the above-mentioned electrolyte solution is injected in a dry atmosphere, and the container is sealed and R5 shown in FIG. A lithium secondary battery (cylindrical lithium secondary battery having an outer diameter of 14.95 mm and a height of 39.7 mm) was manufactured.

Referring to the battery shown in FIG. 1, reference numeral 1 denotes the positive electrode and 2 denotes the negative electrode. However, FIG. 1 does not show a metal foil or the like as a conductive substrate used in manufacturing the positive electrode 1 or the negative electrode 2 in order to avoid complication. The positive electrode 1 and the negative electrode 2 are spirally wound with a separator 3 interposed therebetween, and are housed in a battery case 5 together with the above-mentioned electrolytic solution 4 as a spiral electrode body.

The battery case 5 is made of stainless steel and also serves as a negative electrode terminal. An insulator 6 made of polytetrafluoroethylene is arranged at the bottom of the battery case 5 prior to housing the spiral electrode body. An insulator 7 made of polytetrafluoroethylene is also arranged on the inner peripheral portion of the battery case 5.

The sealing member 8 is made of stainless steel, and a gas vent 8 is provided in the center of the sealing plate 8. The annular packing 9 is made of polypropylene and is arranged on the peripheral edge of the sealing plate 8. The flexible thin plate 10 is made of titanium and has a disk shape, and the peripheral edge is arranged on the annular packing 9. The heat deformable member 11 is annular and made of polypropylene, and is arranged on the flexible thin plate 10. And
The thermally deformable member 11 has an effect of changing the breaking pressure of the flexible thin plate 10 by being deformed by the temperature.

The terminal plate 12 is made of rolled steel and nickel-plated. The terminal plate 12 is provided with a cutting blade 12a and a gas discharge hole 12b. When the internal pressure increases and the flexible thin plate 10 is deformed due to the increase in the internal pressure, the flexible thin plate 10 is broken by the cutting blade 12a, and gas inside the battery is discharged from the gas discharge hole 12b to the outside of the battery. In addition, the battery is designed so as to prevent the battery from being destroyed under high pressure.

The insulator 13 insulates between the battery case 5 and the sealing plate 8, and the lead 14 is made of aluminum. The lead 14 electrically connects the positive electrode 1 to the sealing plate 8. The terminal plate 12 functions as a positive electrode terminal by contact with the sealing plate 8. The lead body 15 is made of copper and electrically connects the negative electrode 2 and the battery case 5.

Example 2 A polytetrafluoroethylene-containing mixture powder was prepared as follows. First, as in Example 1, 90 parts by weight of lithium nickel oxide, 6 parts by weight of flaky graphite, 3 parts by weight of fine powder of polytetrafluoroethylene, 0.5 parts by weight of polyvinyl butyral, and 0.5 parts by weight of polyethylene glycol Was put into a planetary mixer, and the mixture was stirred and mixed in a dry system to prepare a polytetrafluoroethylene-containing mixture powder B.

Next, the polytetrafluoroethylene-containing mixture powder B and 40 parts by weight of a mixed solvent of cyclohexanone and toluene in a weight ratio of 1: 1 as a solvent were put into a ball mill, and mixed by stirring. A sheet-like positive electrode and an R5-type lithium secondary battery were produced in the same manner as in Example 1, except that a paint for formation was prepared and this paint was used.

Comparative Example 1 3 parts by weight of the same fine powder of polytetrafluoroethylene as in Example 1 were previously charged into 40 parts by weight of a mixed solvent of cyclohexanone and toluene at a weight ratio of 1: 1 and stirred and mixed with a homogenizer mixer. Thus, a polytetrafluoroethylene dispersion was prepared.

Next, the above polytetrafluoroethylene dispersion, 90 parts by weight of lithium nickel oxide, 6 parts by weight of flaky graphite, 0.5 parts by weight of polyvinyl butyral, and polyethylene Example 1 was repeated except that 0.5 part by weight of glycol was added and mixed with stirring to prepare a coating for forming a positive electrode coating film.
In the same manner as in the above, a sheet-shaped positive electrode and an R5 type lithium secondary battery were produced.

Comparative Example 2 0.5 parts by weight of polyvinyl butyral and 0.5 parts by weight of polyethylene glycol as in Example 1 were charged with 25 parts by weight of a mixed solvent of cyclohexanone and toluene in a weight ratio of 1: 1. After stirring and mixing, the obtained resin solution was mixed with Example 1
90 parts by weight of lithium nickel oxide, 6 parts by weight of flaky graphite, and 15 parts by weight of a mixed solvent of cyclohexanone and toluene having a weight ratio of 1: 1 as described above are added, and mixed by stirring. And a sheet-shaped positive electrode and an R5-type lithium secondary battery were produced in the same manner as in Example 1 except that this coating material was used.

Comparative Example 3 In place of the fine powder of polytetrafluoroethylene in the positive electrode material of Example 1, 5 parts by weight of polytetrafluoroethylene dispersion (3 parts by weight as the solid content of polytetrafluoroethylene) was used. 0.5 parts by weight of polyvinyl butyral and 0.5 parts of polyethylene glycol
1 part by weight of carboxymethylcellulose was used instead of 40 parts by weight of a mixed solvent of cyclohexanone and toluene, and 38 parts by weight of distilled water was used instead of 40 parts by weight of a mixed solvent of cyclohexanone and toluene.
Parts by weight, 1 part by weight of carboxymethylcellulose, 38 parts by weight of distilled water, 90 parts by weight of lithium nickel oxide, and 6 parts by weight of flaky graphite are added and mixed by stirring to prepare a coating for forming a positive electrode coating film. A sheet-shaped positive electrode and an R5-type lithium secondary battery were produced in the same manner as in Example 1 except that this paint was used.

With respect to the sheet-shaped positive electrodes obtained in Examples 1 and 2 and Comparative Examples 1 to 3 and the R5 type lithium secondary battery, a winding test of the sheet-shaped positive electrode and measurement of the capacity of the battery were performed. Table 1 shows the results. In addition, the winding test method of the sheet-shaped positive electrode and the measuring method of battery capacity are as follows.

Winding test method for sheet-shaped positive electrode: As shown in FIG. 2, stainless steel having a diameter of 3.0 mm (SUS30
4) Wrap the sheet-shaped positive electrode 17 around the rod 16 and make an angle of 90 °.
And observe the outer coating film at the bending point 18,
The presence or absence of cracks in the coating film and the presence or absence of peeling of the coating film from the conductive substrate were examined. Table 1 shows the results.

Measurement method of battery capacity: When the charging / discharging current is indicated by C, charging / discharging was carried out with R5 type at 560 mA as 1C. Charging was performed at a constant voltage of 4.1 V with a 1 C current limiting circuit, and discharging was performed until the voltage between the electrodes of the battery dropped to 2.75 V. And at this time (that is, the first
The discharge capacity at the time of the second charge / discharge) was measured, and the ratio of the discharge capacity of the battery of Example 1 to the discharge capacity of the other batteries was determined as 100%. Table 1 shows that the discharge capacity of Example 1 was 10
The ratio at 0% is shown as the battery capacity (%).

[0063]

[Table 1]

As is clear from the results shown in Table 1 above,
The sheet-shaped positive electrodes of Examples 1 and 2 were free from cracking of the coating film and peeling of the coating film from the conductive substrate in the winding test, and the batteries of Examples 1 and 2 were the same as those of Comparative Examples 1 to 3. Compared to batteries,
The battery capacity was small and the capacity was high.

On the other hand, in Comparative Examples 1 and 2, the final composition of the paint for forming a positive electrode coating film was the same as in Examples 1 and 2, but the winding test showed that There were cracks in the film and peeling of the coating film from the conductive substrate.

In Comparative Example 3 using an aqueous dispersion of polytetrafluoroethylene, no cracks were generated in the coating film of the sheet-like positive electrode and no peeling of the coating film from the conductive substrate was observed in the winding test. However, the battery capacity was significantly reduced.

[0067]

As described above, according to the present invention,
High-capacity lithium secondary with high adhesive strength of the sheet-shaped positive electrode coating, no cracking of the sheet-shaped positive electrode coating in the bending process such as the winding process, and no peeling of the coating from the conductive substrate. A battery can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a lithium secondary battery of the present invention.

FIG. 2 is a view schematically showing a winding test method for a sheet-shaped positive electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte

Claims (1)

[Claims] 1. A sheet positive electrode comprising a conductive substrate on which a coating film containing at least a positive electrode active material and a binder is formed, wherein the binder of the sheet-type positive electrode is soluble in at least polytetrafluoroethylene and an organic solvent. In the manufacture of a lithium secondary battery containing the resin or rubber of the above, at least the positive electrode active material is added in advance to a fine powder of polytetrafluoroethylene, and the mixture is stirred and mixed in a dry manner to prepare a polytetrafluoroethylene-containing mixture powder. At least an organic solvent is added to the polytetrafluoroethylene-containing mixture powder, and a paint prepared by wet-stirring and mixing is applied on a conductive substrate, and dried to form a coated film, thereby producing a sheet-shaped positive electrode. A method for producing a lithium secondary battery.