JPH11144714A - Manufacture of slurry for electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of an electrode surface defects by mixing and dissolving or dispersing a binder to a solvent, and then adding an active material and a conductive agent thereto followed by kneading. SOLUTION: By dissolving a binder to a solvent first, the mass of an active material or conductive agent entangled to the undissolved binder is eliminated, whereby a stripe or surface defect resulted from the mass can be eliminated in the application of a slurry. When the conductive agent and the active material are added to the binder solution followed by kneading, the powder having the larger surface area is preferably added first. Because the one having the larger surface area has a poor kneading efficiency, and a slurry having a more satisfactory dispersed state can be provided by performing the kneading in the state having a low slurry viscosity. The kneading is preferably performed under a reduced pressure, in order to prevent the entanglement of an atmospheric gas, such as air in the slurry from the viewpoint of the prevention of an electrode surface defects such as void after application. However, when the pressure reduction can not be performed with kneading in relation to a device, the slurry may be taken out after the kneading is ended and degassed under reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an electrode slurry, and more particularly, to a method for producing an electrode slurry capable of reducing electrode surface defects after coating.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras and notebook personal computers, demand for small and high capacity secondary batteries has been increasing. Most of the currently used secondary batteries are nickel-cadmium batteries or nickel-hydrogen batteries using an alkaline electrolyte, but the battery voltage is as low as about 1.2 V, and it is difficult to improve the energy density. Therefore, non-aqueous electrolyte secondary batteries such as lithium secondary batteries using lithium metal for the negative electrode and lithium ion secondary batteries have been developed.

[0003] As a method of preparing an electrode slurry used in these batteries, it has been general to knead and knead a solvent, a binder, a conductive agent, an active material and the like all at once.

[0004]

However, in this method,
Due to insufficient kneading or the like, a lump in which the conductive agent and the active material were entangled in the binder undissolved in the solvent was formed, and when applied on the current collector, a streak due to the lump was sometimes formed on the electrode surface. . Further, even if the removal by filtration is attempted, clogging occurs in a short period of time, and kneading for a very long time is required to eliminate the lumps, resulting in an increase in cost.

An object of the present invention is to solve the above problems, and an object of the present invention is to provide a method for producing a slurry for an electrode, in which electrode surface defects are less likely to occur.

[0006]

SUMMARY OF THE INVENTION The present invention has the following arrangement to solve the above-mentioned problems.

[0007] In an electrode slurry comprising an active material, a conductive agent, a binder, and a solvent, a solvent and a binder are mixed and dissolved or dispersed, and then the active material and the conductive agent are added and kneaded. Method for producing electrode slurry. "

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is used for producing an electrode sheet for a positive electrode and a negative electrode, and the obtained electrode can be used as an active electrode of various batteries, such as a primary battery and a secondary battery.
What kind of battery is used is not particularly limited. The form of the battery is not particularly limited, such as a square type, a cylindrical type, a card type, and a coin type.

First, it is necessary to dissolve or disperse the solvent and the binder (hereinafter simply referred to as “dissolution”), but the dissolution method is not particularly limited, and a generally known method is used. For example, the binder is added and dissolved while stirring the solvent with a stirrer or a homomixer. At this time, heating may be performed to accelerate the dissolution, or stirring may be performed while cooling to keep the temperature constant. By dissolving the solvent and the binder first, it is possible to eliminate the clumps in which the active material and the conductive agent are entangled in the undissolved binder, and to eliminate streaks and surface defects caused by the clumps when applying the slurry. be able to. Also, when the slurry is filtered at the time of coating, clogging of the strainer and the filter hardly occurs, which is effective in improving workability.

As the solvent used at this time, chloroform, methylene chloride, ethyl acetate, toluene, xylene, water, N-methyl-2-pyrrolidone (NMP),
N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, 1,3-dioxolan, methyl formate, dimethylimidazolidinone and the like can be appropriately selected depending on the binder used. Examples of the binder include fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride (PVDF), propylene hexafluoride, and copolymers thereof, lignin, carboxycellulose, hydroxycellulose, polyvinyl alcohol, and polyvinyl methyl ether. And water-soluble polymer such as polyvinylpyrrolidone, and others, such as polycarbonates, various polyimides, polymethyl methacrylate, polyacrylonitrile, acrylics such as polyacrylates and copolymers thereof, and thermosetting of phenoxy resins and epoxy resins. Resin is used. Further, a mixture of a thermoplastic resin and a thermosetting resin,
Two or more kinds of thermoplastic resins, two or more kinds of thermosetting resins, and the like are also used. Further, additives such as a reaction initiator, an accelerator, and a stabilizer can be added as needed. The ratio between the binder and the solvent depends on the solubility of the combination of the binder and the solvent, and is not particularly limited.

Next, a conductive agent and an active material are added to the binder solution and kneaded, and it is preferable to add them in order of increasing surface area of the powder to be added. In other words, those having a large surface area (bulky) tend to have poor kneading efficiency, and those kneaded with a low slurry viscosity tend to obtain a slurry having a good dispersion state. In addition, from the viewpoint of preventing overflow from the kneading vessel at the time of addition, it is preferable that a slurry having a large surface area (bulk) is added and kneaded to form a slurry at a stage where the slurry volume is as small as possible.

In general, carbon black such as acetylene black and furnace black, which is used as a conductive agent rather than a positive electrode active material and a negative electrode active material, has a larger surface area, and is added to a container in which a binder is dissolved. The binder may be added directly, or a conductive agent or the like may be charged in a kneading device in advance, and a binder solution dissolved separately may be added.

The kneading apparatus is not particularly limited, but may be a stirrer using a stirring blade, a homogenizer, a homomixer, a mortar, a sand mill, a roll mill, or a stirrer combining these.

From the viewpoint of preventing electrode surface defects such as voids after coating, kneading is preferably carried out under reduced pressure for the purpose of preventing atmospheric gas such as air from being entrapped in the slurry. If the pressure cannot be reduced while kneading due to the equipment, the slurry for the electrode can be taken out and degassed under reduced pressure after kneading. At this time, it is preferable to perform degassing under reduced pressure while shaking or stirring to enhance degassing efficiency. The pressure reduction can be performed by a usual device such as a rotary pump or an aspirator.

[0015] The electrode active material used in the present invention is not particularly limited. As the negative electrode active material, a carbon body is often suitably used. The carbon body used in the present invention is not particularly limited, and generally used is one obtained by firing an organic substance, graphite, or the like. As the form of the carbon body, a powdered or fibrous carbon body is preferably used. Examples of the powdered carbon include natural graphite, artificial graphite, coke such as fluid coke, mesocarbon microbeads, polyacrylonitrile (PAN), polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenolic resin, and furfuryl alcohol. Resin or a resin fired body such as a copolymer thereof, a pitch of coal or petroleum, and a fired body of cellulose are exemplified. Examples of the fibrous carbon body include a PAN-based carbon fiber obtained from PAN or a copolymer thereof, a pitch-based carbon fiber obtained from a pitch such as coal or petroleum, a cellulosic carbon fiber obtained from cellulose, and a gas of a low molecular weight organic substance. And vapor-grown carbon fibers obtained from
Carbon fibers obtained by baking the above-mentioned polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol resin and the like may be used.

Among them, a carbon body satisfying the characteristics is appropriately selected according to the characteristics of the electrode and the battery in which the carbon body is used. In the case where the carbon material is used for a negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt, a PAN-based carbon material, a pitch-based carbon material, and a vapor-grown carbon material are preferable. In particular, a PAN-based carbon body is preferably used in that the doping of an alkali metal ion, particularly, a lithium ion is good.

The particle size of the powdered carbon body is preferably 0.1
To 100 μm, more preferably 1 to 50 μm.
m. The diameter of the carbon fiber should be determined so that it can easily take each form, but preferably 1 to 10
00 μm is used, and it is also preferable to use several types of carbon fibers.

The average length of the carbon fibers is 1 mm or less, preferably 50 μm or less, and more preferably 8 μm or less.
３０30 μm is used. As a lower limit, the ratio of the fiber length to the fiber diameter (aspect ratio) is preferably 1 or more. If the fiber length exceeds 1 mm, the coatability becomes poor when a slurry is formed to form a sheet-like electrode, and when the electrode is used, a short circuit between the positive electrode and the negative electrode easily occurs, which is not preferable. If the aspect ratio is less than 1, the powder will be cleaved in the fiber direction during powdering to expose an active carbon surface, and the cycle characteristics will be poor, which is not preferable. The average length of the fiber, for example, by microscopic observation such as SEM,
It is determined by measuring the length of at least 20 carbon bodies in the fiber direction. In order to cut or pulverize the carbon fiber to 1 mm or less, various pulverizers can be used. As the negative electrode active material, in addition to the carbon body, for example, compounds such as metal oxides and polyacene, metal lithium and alloys thereof as disclosed in JP-A-7-235293 are used as the negative electrode active material.

As the positive electrode active material, artificial or natural graphite powder, inorganic compounds such as carbon fluoride and metal oxides, organic polymer compounds and the like are used. In this case, when an inorganic compound such as a metal oxide is used as the positive electrode,
A charge / discharge reaction occurs using doping and undoping of the cation. In the case of an organic polymer compound, a charge / discharge reaction occurs by doping and undoping of an anion. As described above, various charge / discharge reaction modes are adopted depending on the substance, and these are appropriately selected according to the required positive electrode characteristics of the battery. Specifically, inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals, conjugated polymers such as polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, and polythiophene, polymers having disulfide bonds, and the like And positive electrode active materials used in ordinary secondary batteries. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, cobalt, manganese, nickel, molybdenum, vanadium, chromium,
Transition metal oxides such as iron, copper and titanium and transition metal chalcogens are preferably used. In particular, Li _x CoO ₂ (0
<X ≦ 1.0), Li _x NiO ₂ (0 <x ≦ 1.
0) or a lithium composite oxide obtained by substituting a part of these metal elements with an alkaline earth metal element and / or a transition metal element, Li _x MnO ₂ (0 <x ≦ 1.0),
Li _x Mn ₂ O ₄ (0 <x ≦ 1.3) is preferably used.

The electrode slurry obtained in the present invention is applied on a metal current collector such as aluminum, nickel, stainless steel, and copper. The metal current collector is not particularly limited, such as a foil shape, a fiber shape, and a mesh shape. For example, a sheet-like electrode is produced by applying a slurry on a metal foil. As the coating method, generally known coating methods can be used, for example, a slit die coater,
Various coating methods such as knife coater, lip doctor coater, reverse roll coater, direct gravure, three reverse, doctor reverse, offset gravure, four reverse, kiss reverse, dip, spin, wire bar and the like can be mentioned.

The secondary battery manufactured according to the present invention can be used as a video camera, a personal computer, a word processor, a radio-cassette, a mobile phone, a handy terminal, a CD player, and the like by utilizing the features of light weight, high capacity, and high energy density.
It can be widely used for portable small electronic devices such as MD players, electric shavers, liquid crystal televisions, toys and the like, and portable small electronic devices such as electric vehicles.

[0022]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 An LR-A2000 system manufactured by IKA (stirrer: RE1)
62 / P, homogenizer: ULTRA-TURRAX
T25) is charged with 860 g of NMP and 100 g of PVDF (KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.), and PVD with a stirrer at 50 rpm and a homogenizer at 5000 rpm.
F was dissolved. The stirring was stopped, and acetylene black (“Denka Black”, a product of Denki Kagaku KK), a conductive agent, was added.
5 g of the acetylene black was added with manual stirring with a spatula to reduce the bulk of the acetylene black.
The mixture was kneaded at 30 rpm for 30 minutes. The kneading was stopped, 420 g of artificial graphite (manufactured by Lonza, "KS-25") was added as the negative electrode active material in the same manner as acetylene black, and then short fibrous carbon fibers ("Treca" milled fiber: MLD-30, Toray ( stock)
140 g) was added in the same manner as acetylene black, the pressure in the vessel was reduced to 20 mbar or less, and the mixture was kneaded for 1 hour with a stirrer at 50 rpm and a homogenizer at 8000 rpm to obtain an electrode slurry.

Using the obtained slurry for an electrode, a single-plate knife coater was used to have a thickness of 17 μm, a width of 300 mm, and a length of 700.
When a total of 20 sheets were applied on a copper foil having a thickness of 20 mm, all of the electrode sheets were free from surface defects such as streaks and projections.

Example 2 Lithium hydroxide (Li (OH)), nickel hydroxide (N
i (OH) ₂ ), strontium hydroxide octahydrate (Sr
_{(OH) 2 · 8H 2 O} ), cobalt hydroxide (Co (O
H) ₂ ) in terms of oxide, Li _0.98 Sr _0.002 Ni _0.90 C
o It was weighed so as to be _0.10 O ₂ , held at 650 ° C. for 16 hours, and pre-baked. After cooling to room temperature, the mixture was pulverized again in an automatic mortar for 30 minutes to break up aggregation of secondary particles. Then, in the same atmosphere as in the preliminary firing, main firing was performed at 750 ° C. for 8 hours, cooled to room temperature, and then pulverized again in an automatic mortar to obtain a positive electrode active material powder A.

LR-A2000 system manufactured by IKA (stirrer: RE162 / P, homogenizer: ULTRA-T)
URRAX T25) 800g NMP, PVDF
(KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.)
g Charge stirrer 50 rpm, homogenizer 5000 rpm
m to dissolve the PVDF. The stirring was stopped, and 40 g of acetylene black (“Denka Black”, manufactured by Denki Kagaku KK) as a conductive agent was added with manual stirring with a spatula to reduce the bulk of the acetylene black.
The pressure was reduced to 0 mbar or less, and the mixture was kneaded with a stirrer at 50 rpm and a homogenizer at 8000 rpm for 30 minutes. The kneading was stopped, 1200 g of the above-mentioned positive electrode active material powder A was added in the same manner as acetylene black, the pressure in the vessel was reduced to 20 mbar or less, the stirrer was 50 rpm, and the homogenizer was 8000 rpm.
For 1 hour to obtain an electrode slurry.

Using the obtained slurry for an electrode, a single-plate knife coater was used to have a thickness of 20 μm, a width of 300 mm, and a length of 700.
When a total of 20 sheets were coated on an aluminum foil having a thickness of 20 mm, all the electrode sheets were free from surface defects such as streaks and projections.

Example 3 860 g of NMP was placed in a 2000 cc stainless steel container, and “TK Robomix” manufactured by Tokushu Kika Kogyo Co., Ltd.
(Agitator: TK Homomixer MARKII2.5 type)
While stirring at 4,000 rpm, 100 g of PVDF (KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.) was added to dissolve the PVDF. The stirring was stopped, and 25 g of acetylene black ("Denka Black", manufactured by Denki Kagaku KK) as a conductive agent was added with a spatula while manually stirring to reduce the volume of acetylene black.
The mixture was kneaded at pm for 15 minutes. The kneading was stopped, 420 g of artificial graphite (manufactured by Lonza, "KS-25") was added as the negative electrode active material in the same manner as acetylene black, and then short fibrous carbon fibers ("Treca" milled fiber: MLD-30, Toray ( stock)
140 g) was added in the same manner as acetylene black, and kneaded with a homogenizer at 10,000 rpm for 30 minutes. The container was transferred to a vacuum desiccator as it was, and degassed under reduced pressure for 10 minutes while manually shaking under reduced pressure to obtain a slurry for an electrode.

Using the obtained slurry for an electrode, a single-plate knife coater was used to have a thickness of 17 μm, a width of 300 mm, and a length of 700.
When a total of 20 sheets were applied on a copper foil having a thickness of 20 mm, all of the electrode sheets were free from surface defects such as streaks and projections.

Example 4 800 g of NMP was placed in a 2000 cc stainless steel container, and “TK Robomix” manufactured by Tokushu Kika Kogyo Co., Ltd.
(Agitator: TK Homomixer MARKII2.5 type)
While stirring at 4,000 rpm, 100 g of PVDF (KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.) was added to dissolve the PVDF. The stirring was stopped, and 40 g of acetylene black ("DENKA BLACK", manufactured by Denki Kagaku KK) as a conductive agent was added with a spatula while manually stirring to reduce the bulk of acetylene black.
The mixture was kneaded at pm for 15 minutes. Kneading was stopped, 21200 g of LiCoO as a positive electrode active material was added in the same manner as in acetylene black, and the mixture was kneaded with a homogenizer at 10,000 rpm for 30 minutes. The container was transferred to a vacuum desiccator as it was, and degassed under reduced pressure for 10 minutes while manually shaking under reduced pressure to obtain a slurry for an electrode.

Using the obtained electrode slurry, a single plate knife coater was used to have a thickness of 20 μm, a width of 300 mm, and a length of 700.
When a total of 20 sheets were applied on a copper foil having a thickness of 20 mm, all of the electrode sheets were free from surface defects such as streaks and projections.

Comparative Example 1 LR-A2000 system manufactured by IKA (stirrer: RE1)
62 / P, homogenizer: ULTRA-TURRAX
860 g of NMP, 100 g of PVDF (KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.) and 25 g of acetylene black (“Denka Black”, manufactured by Denki Kagaku Co., Ltd.) as a conductive agent were manually stirred with a spatula in T25). In addition, after lowering the bulk of acetylene black, 420 g of artificial graphite (manufactured by Lonza, "KS-25") was added as a negative electrode active material in the same manner as acetylene black, and then short fibrous carbon fibers ("Treca" milled fiber: MLD-30, Toray Industries, Inc.
140 g) was added in the same manner as acetylene black, the pressure in the vessel was reduced to 20 mbar or less, and the mixture was kneaded for 1 hour with a stirrer at 50 rpm and a homogenizer at 8000 rpm to obtain an electrode slurry.

Using the obtained slurry for an electrode, a single-plate knife coater was used to obtain a 17 μm thick, 300 mm wide, and 700 mm long.
When a total of 20 sheets were applied on a copper foil of 2 mm, surface defects such as streaks and protrusions occurred on 7 electrode sheets.

Comparative Example 2 LR-A2000 system manufactured by IKA (stirrer: RE1)
62 / P, homogenizer: ULTRA-TURRAX
To T25), 800 g of NMP, 100 g of PVDF (KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.), and 40 g of acetylene black (“Denka Black”, manufactured by Electrochemical Co., Ltd.) as a conductive agent were manually stirred with a spatula. In addition, after reducing the bulk of acetylene black,
After adding 1200 g of the positive electrode active material powder A in the same manner as acetylene black, the pressure in the container was reduced to 20 mbar or less,
1 with a stirrer 50 rpm and a homogenizer 8000 rpm
The mixture was kneaded for an hour to obtain an electrode slurry.

Using the obtained slurry for an electrode, a single plate knife coater was used to have a thickness of 20 μm, a width of 300 mm, and a length of 700.
When a total of 20 sheets were coated on a copper foil of 2 mm, surface defects such as streaks and protrusions occurred on eight electrode sheets.

Comparative Example 3 860 g of NMP and P in a 2000 cc stainless steel container
100 g of VDF (KF polymer # 1100 manufactured by Kureha Chemical Co., Ltd.) was added, and 25 g of acetylene black (“Denka Black”, manufactured by Denki Kagaku Co., Ltd.) as a conductive agent was added while manually stirring with a spatula, and the bulk of acetylene black was added. And then artificial graphite (made by Lonza,
After adding 420 g of "KS-25") in the same manner as acetylene black, 140 g of short fibrous carbon fiber ("Treca" milled fiber: MLD-30, manufactured by Toray Industries, Inc.) was added in the same manner as in acetylene black. "TK Robomix" (stirring unit; TK homomixer MARK)
II2.5 type) and rotation speed from 1400 rpm to 10000
The mixture was slowly raised to rpm and kneaded at 10,000 rpm for 30 minutes. The container was transferred to a vacuum desiccator as it was, and degassed under reduced pressure for 10 minutes while manually shaking under reduced pressure to obtain a slurry for an electrode.

Using the obtained electrode slurry, a single-plate knife coater was used to obtain a film having a thickness of 17 μm, a width of 300 mm, and a length of 700.
When a total of 20 coatings were applied on a copper foil having a thickness of 20 mm, surface defects such as streaks and protrusions occurred on 10 electrode sheets.

[0038]

EFFECTS OF THE INVENTION By adopting the method for producing a slurry for an electrode of the present invention, a lump in which a conductive agent and an active material are entangled in a binder not dissolved in a solvent due to insufficient kneading or the like is less likely to be formed. As a result, the occurrence of electrode surface defects can be reduced.

Claims (9)

[Claims] 1. An electrode slurry comprising an active material, a conductive agent, a binder, and a solvent, wherein the solvent and the binder are mixed and dissolved or dispersed, and then the active material and the conductive agent are added and kneaded. A method for producing an electrode slurry. 2. The method for producing an electrode slurry according to claim 1, wherein after the solvent and the binder are mixed and dissolved or dispersed, the active material and the conductive agent are added and kneaded in order of increasing surface area. 3. The method for producing a slurry for an electrode according to claim 1, wherein the kneading is performed under reduced pressure. 4. The method for producing a slurry for an electrode according to claim 1, wherein after the kneading, defoaming is performed while shaking under reduced pressure. 5. The method for producing an electrode slurry according to claim 1, wherein the active material is a lithium composite oxide. 6. The method according to claim 1, wherein the lithium composite oxide is Li _x CoO _2.
(0 <x ≦ 1.0), Li _x NiO ₂ (0 <x ≦ 1.
The method for producing an electrode slurry according to claim 5, wherein 0) or a part of these metal elements is replaced with an alkaline earth metal element and / or a transition metal element. 7. The method for producing an electrode slurry according to claim 1, wherein the active material is a carbon body. 8. The method for producing a slurry for an electrode according to claim 7, wherein said carbon body is a mixture of carbon fibers and a crystalline carbon material. 9. A method for producing an electrode, comprising using the slurry for an electrode obtained according to any one of claims 1 to 8.