Electrode and gel electrolyte cell production method

Details Electrode and gel electrolyte cell production method Electrode and gel electrolyte cell production method

2000-11-08

2004-10-19

Ryan, Patrick (Department: 1745)

Metal working

Method of mechanical manufacture

Electrical device making

C429S162000, C429S300000

Reexamination Certificate

active

06805720

ABSTRACT:

BACKGROUND OF THE INVENTION
The present application claims priority to Japanese Application No. P11-318434 filed Nov. 9, 1999, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to production method of an electrode including an electrode carrier and a gel electrolyte film formed on the electrode carrier and having a larger width than the electrode carrier and a production method of a gel electrolyte cell having such an electrode.
2. Description of the Prior Art
Recently various portable electronic apparatuses such as a tape recorder provided with a camera, a cellular telephone, and a portable computer are used and it has been desired to reduce their weight and size. Accordingly, it is also desired to reduce size and weight of cells used as a power source of these electronic apparatuses. To cope with this, a lithium-ion cell has been developed and industrialized. This cell uses a porous polymer separator impregnated in an electrolyte solution as the ion conductor between the positive electrode and negative electrode. In order to prevent leak of the electrolyte solution, the cell is packaged in a heavy metal package.
On the other hand, a great expectation is posed on a solid electrolyte cell using a solid electrolyte as the ion conductor between the positive electrode and negative electrode which has no danger of liquid leak and can be placed in a simplified package to reduce the size and weight of the cell. Especially great attention is paid to a solid polymer electrolyte having lithium salt dissolved in a polymer and a gel-like solid electrolyte containing electrolyte in a matrix polymer (hereinafter, referred to as a gel electrolyte).
A gel electrolyte cell using such a gel electrolyte can be produced as follows.
Firstly, for the positive electrode, a positive electrode composite agent containing a positive electrode active material, conductive agent, and a binder is uniformly applied onto both surfaces of a positive electrode collector and dried so as to form a positive electrode active material layer, which is dried and pressed by a roll press so as to obtain a positive electrode sheet.
Next, for the negative electrode, a negative electrode composite agent containing a negative electrode active material and a binder is uniformly applied onto both surfaces of a negative electrode collector and dried to form a negative electrode active material layer, which is dried and pressed by a roll press so as to obtain a negative electrode sheet.
As for the gel electrolyte film, a sol electrolyte solution containing a non-aqueous solvent, electrolyte salt, and matrix polymer is uniformly applied onto both surfaces of the positive electrode sheet and the negative electrode sheet and dried to remove the solvent. Thus, a gel electrolyte film is formed on the positive electrode active material layer and the negative electrode active material layer.
The positive electrode sheet having the gel electrolyte film is, for example, cut into a strip. Furthermore, the gel electrolyte film and the positive electrode active material layer of the portion for a positive electrode lead welding is removed from the surface of the positive electrode collector, and the positive electrode lead is welded here, so as to obtain a strip positive electrode having the gel electrolyte film.
Moreover, the negative electrode sheet having the gel electrolyte film is, for example, cut into a strip. Furthermore, the gel electrolyte film and the negative electrode active material layer of the portion for a negative electrode lead welding is removed from the surface of the negative electrode collector, and the negative electrode lead is welded here, so as to obtain a strip negative electrode having the gel electrolyte film.
Lastly, the strip positive electrode and the strip negative electrode each having the gel electrolyte film are laid upon one another and the layered body is rolled in the longitudinal direction by several turns so as to obtain a rolled electrode body. This rolled electrode body is sandwiched by exterior films, whose outermost peripheries are heat-sealed under a reduced pressure so that the rolled electrode body is airtightly sealed in the exterior films to complete the gel electrolyte cell.
In the rolled type gel electrolyte secondary cell having the aforementioned configuration, the gel electrolyte film formed on the electrode surface is defined so as to have a larger width than the electrode so as to improve reliability of the operation of the cell.
In order to obtain the aforementioned width of the gel electrolyte film, various trials have been made to increase the dimensional accuracy of the gel electrolyte coating apparatus and the accuracy of the coating position. However, due to the gel viscosity fluctuations and the porosity and the surface roughness fluctuations of the electrode to which the gel electrolyte is to be applied, it is difficult to obtain a stable dimensional accuracy of the gel electrolyte film. The gel electrolyte film often has a too large width to be placed in a package when assembling the cell or too small width, causing a short circuit between the positive electrode and the negative electrode.
Moreover, in order to solve this problem, there is a method to form the gel electrolyte film having a sufficiently larger width than the electrode and then cut off an excessive portion of the gel electrolyte film using a roller cutter or removed using a brush or scraper. However, this has caused various problems such that a portion of the gel electrolyte film to be left is removed or a portion of the gel electrolyte film which has been cut off is mixed into the cell, lowering the yield.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electrode production method and a gel electrolyte cell production method capable of forming a gel electrolyte film on the electrode with a stable high accuracy.
The electrode production method according to the present invention is for producing an electrode including a rectangular electrode carrier and a gel electrolyte film formed on the electrode carrier and having a width greater than the electrode carrier, the method including: an overlaying step for overlaying a first carrier having a greater width than the gel electrolyte film, a second carrier having a width approximately identical to that of the gel electrolyte film, and the electrode carrier in this order; a coating step for applying an electrolyte composition onto the first carrier, the second carrier, and the electrode carrier which have been put upon one another, in such a manner that the applied electrolyte composition has a width greater than the width of the second carrier and smaller than the width of the first carrier; a first peel-off step for peeling off from the first carrier the second carrier and the electrode carrier coated with the gel electrolyte composition in the coating step and overlaid on each other; a gelatinization step for gelatinizing into a gel electrolyte film the electrolyte composition applied onto the second carrier and the electrode carrier which have been peeled off from the first carrier in the first peel-off step, and a second peel-off step for peeling off from the second carrier the gel electrolyte film and the electrode carrier.
In the aforementioned electrode production method according to the present invention utilizing the difference in adhesion between the first carrier, the second carrier, and the electrode carrier with the electrolyte composition or the gel electrolyte film, the gel electrolyte film is formed on the electrode carrier with a high accuracy without peeling off of the gel electrolyte film from the electrode carrier.
Moreover, the gel electrolyte cell production method uses an electrode including a rectangular electrode carrier and a gel electrolyte film formed on the electrode carrier and having a width greater than the electrode carrier, the electrode being produced by: an overlaying step for overlaying a first

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