JPH09167614A - Manufacture of composite electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obviate a drying process and a recovering device of a solvent of a high polymer by applying complex paste by kneading a binding agent solution and an electrode active material onto a current collecting body, and setting it not more than a temperature at which a binding agent can dissolve in electrolyte. SOLUTION: Mixed powder of a positive electrode active material and a conductive material is heated by a hot plate, and electrolyte in which a fluororesin is dissolved is added/mixed by 30wt.% to/in the mixed powder 70wt.%, and complex paste is formed. After this complex paste is applied onto a heated aluminium foil current collecting body 3, it is cooled in a dry air atmosphere. At this time, it is set not more than a temperature at which a binding agent can dissolve in electrolyte. Then, a fluororesin being a binding agent is deposited, and fills up a void between activating particles, and the particles are firmly bound to each other, and a solid-state positive electrode 1 is formed. Carbon is used as an active material, and processing which is the same as the positive electrode is performed, and the complex paste is heated, and is applied onto a copper foil current collecting body 4, and when it is cooled further in the same way as the positive electrode, a solid-state negative electrode 2 is formed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a composite positive electrode and a composite negative electrode used in a lithium battery or the like.

[0002]

_2. Description of the Related Art Electrodes of conventional non-aqueous secondary batteries are composed of positive electrode active material particles such as LiCoO ₂ , conductive agent powder such as acetylene black (hereinafter referred to as AB) and polar polymers such as polyethylene oxide. , A polymer solid electrolyte in which a salt such as LiPF ₆ is dissolved or a mixture of a polymer such as polyvinylidene fluoride or polyacrylonitrile with a gel electrolyte in which a non-aqueous electrolyte is retained. As for the negative electrode, lithium metal, a layer of the above-mentioned polymer solid electrolyte or gel electrolyte is arranged on the surface of the lithium alloy, or particles such as a metal or carbon or transition metal chalcogen compound capable of occluding and releasing lithium and the polymer solid electrolyte. And was formed from a mixture of gel electrolytes. In all of these, the active material or the mixed powder of the active material and the conductive agent is in direct contact with the polymer solid electrolyte or gel electrolyte. In any case, the polymer that constitutes the polymer solid electrolyte or gel electrolyte is dissolved in a solvent such as acetonitrile or tetrahydrofuran, the solution and active material particles are mixed, and the mixture is applied onto a current collector and then dried. Then, the solid electrode was formed by removing the solvent.

[0003]

In the positive electrode and the negative electrode having the above-mentioned conventional structure, there is a drawback that the active material particles are poorly contacted with the polymer solid electrolyte or gel electrolyte and the interface impedance is high. That is, the solution viscosity of the polymer is high,
There is a drawback that the surface of the active material particles having fine irregularities is not sufficiently wetted by the solution. Further, in the drying step after coating, volume contraction occurs in the solid electrolyte or gel electrolyte,
There is a drawback that the active material particles are separated from the surface. Further, swelling of the polymer occurs in the step of injecting the electrolyte solution after drying, which causes the active material layer to peel from the current collector.

As a method of solving this, US Pat. No. 52
No. 96318 describes an electrode manufacturing method in which an electrolyte solution is mixed with a tetrahydrofuran solution of a fluororesin, a paste in which active material particles are mixed with the solution is applied on a current collector, and then the tetrahydrofuran is dried and removed to form a gel. Has been done. However, with this method, although the subsequent liquid injection step can be omitted, precise control of the evaporation amount of the solvent is required, which is technically difficult in terms of production. As described above, the conventional electrode manufacturing method requires a step of drying a polymer solvent, and a drying device and a device for recovering the evaporated solvent.

[0005]

According to the present invention, a certain kind of fluororesin is not dissolved in an electrolytic solution at room temperature, but its solubility increases with an increase in temperature, and when the solution is returned to room temperature. It was completed by paying attention to the fact that fluororesin as a binder deposits and becomes a solid solid. In particular, polyvinylidene fluoride and propylene hexafluoride are materials which are not dissolved at 60 ° C. or lower, which is a temperature at which batteries are usually used, and which are excellent in binding force and are suitable as a binder. That is,
After the binder is dissolved in the electrolytic solution at a temperature higher than 60 ° C., active material particles are mixed with the binder solution at the same temperature to form a composite paste, and the composite paste is applied onto a current collector. By cooling and depositing the binder, a solid composite layer is formed and an electrode is produced. The electrode thus manufactured has excellent high temperature characteristics because the remelting temperature of the fluororesin as the binder is higher than the initial melting temperature. In addition, since the mixture is kneaded at a high temperature and applied on the current collector at a high temperature, the binding of the binder to the active material particles and the current collector is good. Moreover, the deposited binder is mechanically strong, and an electrode excellent in binding with the current collector and binding with the active material particles can be formed. Therefore, the non-aqueous secondary battery using this is excellent in electrical characteristics such as capacity and cycle characteristics. Moreover, the drying process is not required, and the battery manufacturing process can be simplified.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

(Invention 1) In the present invention, Li is used as the positive electrode active material.
CoO ₂ powder is used. That is, ₂ to 2 in LiCoO ₂ powder
10 wt% AB is added as a conductive agent and mixed in a ball mill for about 1 hour. The mixed powder is dried at a temperature of 110 ° C. for 8 hours.

As the binder, a copolymer of polyvinylidene fluoride, which is one of fluororesins, and propylene hexafluoride was used. This copolymer is used as ethylene carbonate (hereinafter, referred to as EC), diethylene carbonate (hereinafter, referred to as DEC), dimethylene carbonate (hereinafter, referred to as EC).
A mixed solution of DMC) and 1 mol of LiPF ₆ are dissolved in an electrolytic solution at a weight ratio of 1: 9 and dissolved at a temperature of 100 ° C.

The mixed powder of the positive electrode active material and the conductive agent described above
Heated on a hot plate at 00 ° C to give 70 wt% of the mixed powder.
% Of the electrolyte solution in which the above-mentioned fluororesin is dissolved and mixed to form a composite paste. After applying the formed composite paste on the heated aluminum foil,
Cool in a dry air atmosphere. By cooling, the fluororesin as a binder is deposited while containing the electrolytic solution. As a result, the precipitated fluororesin fills the voids of the active material particles and firmly bonds the particles to each other to form a solid positive electrode.

Graphite carbon is used as the negative electrode active material. That is, the dried carbon powder is heated on a hot plate at 100 ° C., and 30 wt% of the electrolytic solution in which the fluororesin is dissolved is added to 70 wt% of the carbon powder and mixed,
Form a composite paste. The formed composite paste is applied on a heated copper foil and then cooled in a dry air atmosphere. By cooling, the fluororesin as a binder is deposited while containing the electrolytic solution. As a result, the deposited fluororesin fills the voids of the active material particles and firmly binds the particles to each other to form a solid negative electrode.

At least one surface of the positive electrode or the negative electrode is coated with 1 mol of LiP in a mixed solution of EC, DEC and DMC.
A solution prepared by mixing an electrolytic solution containing F ₆ and a bifunctional or trifunctional ethylene oxide monomer in a weight ratio of 3: 1 is applied and then irradiated with an electron beam (hereinafter referred to as EB) to be cured. The positive electrode and the negative electrode produced in this way were stacked to assemble a film battery having a size of 30 × 30 mm and a thickness of 0.3 mm. A schematic sectional view of the battery is shown in FIG. FIG.
1, 1 is a positive electrode, 2 is a negative electrode, 3 is an aluminum current collector, 4 is a copper current collector, 5 is a polymer solid electrolyte separator,
6 is a package.

(Invention 2) A positive electrode and a negative electrode were produced by the same procedure as in the above-mentioned Invention 1. A microporous polyethylene film was used as the separator. After stacking the positive electrode, the separator, and the negative electrode, the positive electrode, the separator, and the negative electrode were housed in a battery case, and an electrolyte solution in an amount corresponding to the absorption amount of the separator, that is, 1M LiPF ₆ dissolved in an EC and DEC mixed solvent was injected. In the battery thus produced, neither swelling of the electrode nor separation of the composite layer from the current collector was observed.

(Comparative Example) In this comparative example, the same fluororesin as that used in Invention 1 is dissolved in tetrahydrofuran in a weight ratio of 1: 9. 1 to a mixed solution of the solution and EC, DEC, DMC
A solution prepared by mixing an electrolyte solution in which 1 mol of LiPF ₆ is dissolved at a weight ratio of 1: 1 and the same positive electrode active material mixed powder of the present invention 1 are mixed at a weight ratio of 7: 3 to form a composite paste. To do. The formed composite paste is applied on an aluminum foil and heated to remove tetrahydrofuran by evaporation. The fluororesin formed by heating fills the voids of the active material particles to form a solid positive electrode.

Graphite carbon is used as the negative electrode active material particles.
That is, the same mixed solution as described above and carbon powder are mixed in a weight ratio of 7: 3 to form a composite paste. After coating the formed composite paste on a copper foil, it is heated to remove tetrahydrofuran by evaporation. The fluororesin formed by heating fills the voids of the active material particles to form a solid negative electrode.

A polymer solid electrolyte separator was formed on the surface of the positive electrode or the negative electrode in the same manner as in the present invention 1, and then these were laminated to assemble a film battery. A cycle test was performed using the batteries of the present invention 1, the present invention 2, and the comparative example. The result is shown in FIG. As is clear from FIG. 2, the batteries of the present inventions 1 and 2 have improved battery capacity and stable cycle characteristics as compared with the batteries of the comparative examples.

Six of the batteries of Invention 1, Invention 2 and Comparative Example
The discharge capacity at 0 ° C. is shown in FIG. It can be seen from FIG. 3 that the batteries of Inventions 1 and 2 have improved high temperature characteristics as compared with the batteries of Comparative Example.

[0017]

According to the present invention, a composite paste is prepared at a high temperature and then cooled to fill the voids of the active material with the deposited fluororesin layer, thereby improving the adhesion between the active material particles. , Stable cycle characteristics can be obtained. Also,
The deposited fluororesin does not re-dissolve unless the temperature reaches 100 ° C. or higher, so that the high temperature characteristics of the battery are excellent.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a battery of the present invention.

FIG. 2 is a diagram showing capacity characteristics and cycle life characteristics of the batteries of Examples 1 and 2 and Comparative Example.

FIG. 3 is a diagram showing high temperature characteristics at 60 ° C. of the batteries of Examples 1 and 2 and Comparative Example.

[Explanation of symbols]

 1 Positive Electrode 2 Negative Electrode 3 Aluminum Current Collector 4 Copper Current Collector 5 Polymer Solid Electrolyte Separator 6 Package

Claims (3)

[Claims] 1. A method for producing a composite electrode, wherein a composite layer comprising an electrode active material and a binder is formed on a current collector, and the binder is heated and melted at a temperature at which it can be dissolved in an electrolytic solution. A solution is prepared, the binder solution and the electrode active material are kneaded to form a composite paste, and the composite paste is applied onto a current collector, and then the temperature at which the binder is soluble in the electrolytic solution or lower. A method of manufacturing a composite electrode, comprising: 2. The method for producing a composite electrode according to claim 1, wherein the binder is a fluororesin. 3. The method for producing a composite electrode according to claim 2, wherein the fluororesin is polyvinylidene fluoride, propylene hexafluoride, or a copolymer of polyvinylidene fluoride and propylene hexafluoride.