JP3078960B2 - Electrode manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to batteries, capacitors,
The present invention relates to a method for producing an electrode used for an electrochemical element such as a sensor, a display element, and a recording element, particularly, an electrode used for an organic electrolyte battery.

[0002]

2. Description of the Related Art By using a solid electrolyte, it is possible to obtain a solid electrochemical device such as a small and thin battery or an electric double layer capacitor without liquid leakage. Solid electrolyte materials can be broadly classified into inorganic and organic polymer materials. The organic polymer solid electrolyte is lighter than the inorganic solid electrolyte, and is excellent in flexibility and moldability. The polymer solid electrolyte has ion conductivity, and is initially a solution which has been solidified by heating, irradiation, addition of a polymerization initiator, or the like. Research is being conducted on materials that exhibit high ionic conductivity comparable to inorganic solid electrolytes while taking advantage of the characteristics of polymer solid electrolytes that are lightweight, flexible, and excellent in moldability. In particular, since a solid secondary battery having a high energy density of 3 volts or more can be expected in combination with a negative electrode using lithium as an active material, application studies on batteries are being actively conducted.

[0003]

In the case of using a liquid electrolyte, the polarization of the electrode does not increase,
When a solid electrolyte is used, the affinity between the electrode material and the electrolyte material affects the polarization of the electrode. If the affinity between the electrode material and the electrolyte material is poor, a good electron and ion network is not formed in the solid electrode composition, and the polarization of the electrode increases. As described above, the more uniformly and finely the respective materials are dispersed in the solid electrode composition, the higher the reaction efficiency of the electrode. If the particle size of each functional material in the solid electrode composition is large and the dispersion state is poor, the concentration polarization of the electrode active material increases with charge / discharge cycles, resulting in deterioration of cycle characteristics and reaction efficiency.

Accordingly, an object of the present invention is to provide an electrode containing a solid electrolyte having high reaction efficiency and excellent charge-discharge cycle characteristics.

[0005]

The present invention SUMMARY OF] is an organic electrolyte containing a polymer of at least acrylonitrile polymerization component, N, N'-dimethylformamide and the acetonitrile at a weight ratio of 0.2: 0.8 0.7: 0.3
A method for producing an electrode, comprising uniformly dispersing an electrode active material powder in a liquid diluted with a mixed solvent mixed together , and then heating and drying to form a film. Here, N, weight ratio to the total amount of the electrolyte and the electrode active material powder of the mixed solvent of N'- dimethylformamide and acetonitrile are preferably 2.0 to 10.

Further, as the polymer, a copolymer of acrylonitrile and a monomer selected from the group consisting of methyl acrylate and methyl methacrylate and vinyl acetate, or polyacrylonitrile is used. further,
As the above-mentioned electrode active material, a disulfide compound, in particular, a mixture of polyaniline and a carbon material is preferable.

[0007]

The polymer represented by polyacrylonitrile is mixed with an organic electrolyte comprising an electrolyte salt and an organic solvent, and heated to 60 to 80 ° C. to form a polymer solid electrolyte gel film. it can. However, when the heating temperature increases or the heating time increases, the film deteriorates. A solid electrolyte gel using a polymer containing acrylonitrile as a polymerization component has a high ionic conductivity of about 10 ^-3 and does not inhibit the reaction of an electrode active material, for example, a disulfide compound. Can be used as Therefore, by selecting this as a solid polymer electrolyte and uniformly dispersing the components in the composite membrane, the efficiency of the electrode reaction is increased and the charge / discharge cycle characteristics can be improved. The acrylonitrile polymer and the organic electrolyte alone have a high viscosity and cannot uniformly disperse the electrode active material powder. The above conditions can be satisfied if the components in the composite film can be uniformly dispersed, and a composite film can be prepared using a solvent for the acrylonitrile polymer that evaporates after the film is formed and does not remain in the film.

The present inventors have found that a mixed solvent of N, N'-dimethylformamide and acetonitrile is the most suitable solvent for the acrylonitrile polymer. Acetonitrile is a good solvent for the acrylonitrile polymer and has a boiling point of 81.6 ° C., which is a temperature range suitable for film formation. However, since acrylonitrile gels when the concentration is reduced due to the limitation of dilution, a large amount of electrode active material powder cannot be included. N, N'-dimethylformamide is a good solvent for the acrylonitrile polymer, and the acrylonitrile polymer does not gel even at a low concentration. However, since the boiling point is 153 ° C., which is a somewhat high temperature as a volatile solvent for film formation, the acrylonitrile polymer may be deteriorated. The mixed solvent of N, N'-dimethylformamide and acetonitrile can uniformly disperse the previously ground and mixed electrode active material powder in the polymer electrolyte using the acrylonitrile polymer by taking the above mixing ratio. In addition, a self-supporting film free from deterioration of the acrylonitrile polymer can be obtained.

[0009]

Embodiments of the present invention will be described below. Example 1 (1) Preparation of Powder for Positive Electrode 10 g of 2,5-dimercapto-1,3,4-thiadiazole (DMcT), which is a kind of disulfide compound, and 5.6 g of lithium hydroxide were dissolved in 200 ml of water. Liquid. On the other hand, 17 g of iodine and 34 g of lithium iodide were added to 400 g of water.
Dissolve it in ml to make solution B. Solution B is added dropwise to Solution A, and after the addition is completed, stirring is continued at room temperature for about 2 hours to cause a reaction. After the reaction, the precipitate is filtered off with suction, the unreacted iodine is washed off with hexane and then with acetone, and then further washed with water. The reaction thus obtained is vacuum dried at 60 ° C. for 8 hours. Thus, a polymer of DMcT (p-DMc
T) 9 g are obtained. To 4.5 g of the above polymer p-DMcT, 4 g of polyaniline and 0.6 g of acetylene black are added, and the mixture is lightly ground in a mortar, and then about 40 g of acetonitrile is added to form a slurry. Put this slurry in a ball mill container, and put it together with balls for ball milling for about 5 minutes.
Stir for 0 hours. After stirring, acetonitrile of the mixed solution in the container was volatilized by an evaporator, and powder for composite positive electrode was used.
8 g are obtained.

(2) Preparation of powder dispersion for positive electrode 2.33 g of LiBF _{4 in} a mixed solvent of 10.47 g of propylene carbonate and 7.86 g of ethylene carbonate
Dissolve to prepare an organic electrolyte. To this organic electrolyte was added 3 g of a copolymer of acrylonitrile and methyl methacrylate at a molar ratio of 20: 1 (weight average molecular weight: about 50,000, hereinafter referred to as PAN-A), and the mixture was heated to 80 ° C. and polymer solid electrolyte solution (SPE) was added. -Prepare A). 5 g of N, N'-dimethylformamide is added to 5 g of the polymer solid electrolyte solution.
On the other hand, 2.5 g of the composite positive electrode powder and 5 g of N, N'-dimethylformamide were kneaded in a mortar, and 5 g of the polymer solid electrolyte solution to which the N, N'-dimethylformamide solution was added was added. After mixing, 15 g of N, N'-dimethylformamide and 20 g of acetonitrile are added and stirred. This mixed solution is transferred to a ball mill container, and stirred by a ball mill for 72 hours.

(3) Preparation of Electrode The mixture prepared above was cast, dried under reduced pressure at 60 ° C. for 1 hour, and further dried under vacuum at 70 ° C. for 1 hour to form a film having a thickness of 20 μm.
A positive electrode film of 0 μm is obtained. (4) Preparation of Electrolyte Membrane 10 g of acetonitrile was added to 24 g of the polymer solid electrolyte solution (SPE-A), mixed and stirred, and the solution was cast and vacuum dried at 60 ° C. for 1 hour. The cast solution is transferred to a refrigerator and left for 10 hours. Thus, an electrolyte membrane having a thickness of 300 μm is obtained.

(5) Production of Battery A lithium metal foil having a thickness of 100 μm is used for the negative electrode. Each of the composite positive electrode membrane, electrolyte membrane and metallic lithium foil has a diameter of 1
A 3 mm disc is punched out, and the electrolyte membrane is sandwiched between the lithium anode and the composite cathode membrane. This is placed in a metal container and sealed with a sealing material to form a test battery. This battery is designated as A.

Comparative Example 1 The composite positive electrode powder of Example 1 and the polymer solid electrolyte solution (SPE-A) were kneaded using only acetonitrile. If the amount of acetonitrile is twice or more the weight ratio with respect to the polymer electrolyte solution, the electrolyte solution gels. In this case, the mixture does not become liquid enough to perform ball milling, and therefore, is kneaded in a mortar. This mixed solution is cast to obtain a composite positive electrode film. This is combined with the same electrolyte membrane and lithium foil as in Example 1 to obtain Battery B.

Comparative Example 2 2.5 g of the composite positive electrode powder of Example 1 and 2.5 of the solid polymer electrolyte solution (SPE-A)
g and dilution solvent N, N'-dimethylformamide 42.5
g. N, N'-dimethylformamide has no upper limit of dilution with respect to the copolymer (PAN-A). But,
Since the boiling point is high, a cast film cannot be formed under the same conditions as in Example 1, but can be formed by vacuum drying at 80 ° C. for 4 hours. Using this composite positive electrode film, a test battery C is prepared in the same manner as in Example 1.

Regarding the batteries of the above Examples and Comparative Examples,
FIG. 1 shows the results of a charge / discharge test performed between 4.05 V and 2.5 V at a current of 270 μA. It is clear that when the positive electrode according to the present invention is used, the energy density is high and the life is long.

In the above embodiment, a disulfide compound was used as an electrode active material. However, the present invention is not limited thereto, and LiCoO ₂ , LiNiO ₂ , LiMnO ₂ ,
Use a material that causes redox by electrolysis, such as a metal oxide such as V ₂ O 5, or a conductive polymer such as polyacetylene, polythiophene, or polypyrrole; or an electrode material such as activated carbon that has an action of forming an electric double layer and storing electricity. The case can also be applied. As the disulfide compound, not only the exemplified 2.5-dimercapto-1,3,4-thiadiazole but also many other compounds can be used. For example, triazine, dithiouracil, dithiodimorpholine and the like. There is no problem even if these compounds are oxidized and used in a polymer state. Further, it may be started from the state of the lithium salt. As in the example above,
If necessary, a conductive material can be contained in the electrode.

In the embodiment, polyaniline and a carbon material are used as conductive materials, but many other conductive agents can be used. Other carbon materials, conductive polymers, metal oxides, metal powders and the like can be used.
Carbon materials include natural graphite, artificial graphite, amorphous carbon,
Any of fibrous, powdery, petroleum pitch type, and coal coke type can be used. The shape of the conductive material may be particulate or fibrous. Polyaniline may be prepared by any of electrolytic polymerization and chemical polymerization, and the preparation method is not limited to the examples. Polyaniline is a generic term for those having a polyaniline structure in the main chain skeleton of a polymer. For example, the constituent unit of the polymer may be other than aniline, such as N-methylaniline, N-ethylaniline, or a copolymer thereof.

The acrylonitrile polymer is a generic term for a polymer having a acrylonitrile structure in the main chain skeleton of a polymer, including a copolymer. The degree of polymerization is not limited to those of Examples. In the examples, propylene carbonate and ethylene carbonate were used as the organic solvent, but as the organic solvent used for the polymer electrolyte, dimethyl sulfoxide, sulfolane, dimethoxyethane, 2-methyltetrahydrofuran, γ-butyrolactone, acetonitrile and the like were used. And two or more of these may be used in combination. However, it must be compatible with N, N'-dimethylformamide and acetonitrile. In the examples, LiBF ₄ was used as the electrolyte salt used for the electrode, but other usable electrolyte salts were LiCF ₃ SO ₃ and LiC
10 ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , (C
₂ H _{5) 4} NClO _4, include _{(C 2 H 5) 4 NBF} 4 , and the like.

When a disulfide compound is used as an electrode active material, a disulfide compound, polyaniline, and a carbon material that have been previously ground and mixed and powdered are dispersed as a mixed powder for an electrode active material in a polymer electrolyte of an acrylonitrile polymer. It is desirable. Disulfide compounds undergo a redox reaction, but do not have electronic conductivity. The carbon material, polyaniline, conducts electrons in the electrode. In an electrode in which the function of such a material is specified, the more uniformly and finely each material is dispersed, the higher the reaction efficiency of the electrode.
If the disulfide compound, polyaniline, and carbon material are directly mixed with a polymer solution of an acrylonitrile polymer without being pulverized and mixed in advance, the powder itself is not uniform, so the dispersion of each material in the electrode is biased, and the electrode reaction is smooth. Will not progress. For this purpose, a disulfide compound, polyaniline, and a carbon material that have been pulverized, mixed and powdered in advance are used for the electrodes.

Although the method of pulverization and mixing was carried out by a ball mill in the examples, the method is not limited to this, and pulverization and mixing may be carried out by other dispersion methods such as a homogenizer and a disperser. In the embodiment,
Prior to heating and drying to obtain an electrode film from the dispersion of the electrode active material powder, the dispersion was cast, but printing can also be performed.

[0021]

As described above, according to the present invention, it is possible to obtain an electrode in which the electrode active material is uniformly dispersed in the composite film, the reaction efficiency is high, and the charge / discharge cycle characteristics are improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing charge and discharge characteristics of a lithium battery using a positive electrode according to an example of the present invention and a battery using a positive electrode of a comparative example.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-136711 (JP, A) JP-A-4-359865 (JP, A) JP-A-5-3137 (JP, A) JP-A-5-137 94818 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/60 H01B 1/12

Claims (4)

(57) [Claims] The method according to claim 1 the organic electrolyte comprising a polymer and at least acrylonitrile polymerized moieties, N, and N'- dimethylformamide and acetonitrile at a weight ratio of 0.2:
0.8 to 0.7: in the liquid was diluted with 0.3 solvent mixture in a ratio of, after uniformly disperse the electrode active material powder,
A method for producing an electrode, comprising heating and drying to form a film. Wherein N, N'-dimethylformamide and process according to claim 1, wherein the electrode weight ratio to the total amount of the electrolyte and the electrode active material powder of the mixed solvent of acetonitrile is 10 2.0 . 3. The method according to claim 1, wherein the electrode active material is a mixture of a disulfide compound, polyaniline, and a carbon material. 4. The polymer according to claim 1, wherein the polymer is a copolymer of acrylonitrile with one selected from the group consisting of methyl acrylate, methyl methacrylate and vinyl acetate, or polyacrylonitrile. 3. The method for producing an electrode according to item 1.