Method of producing an electrode

Details Method of producing an electrode Method of producing an electrode

2000-09-25

2003-12-23

Ortiz, Angela (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Forming electrical articles by shaping electroconductive...

Reexamination Certificate

active

06667000

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of producing an electrode for a non-aqueous electrolyte battery, and more particularly to a method of producing, with a high productivity, an electrode for a non-aqueous electrolyte battery, which electrode is excellent in mechanical strength.
BACKGROUND ART
In accordance with scale reduction and weight reduction of various electronic devices such as OA machines, VTR cameras, portable phones and the like in recent years, there is a demand for higher performance of a secondary battery used in these electronic devices. In order to meet these demands, lithium ion secondary batteries are rapidly being developed for practical use as non-aqueous electrolyte batteries having a high discharge potential and a high discharge capacity.
Each of the positive electrode and the negative electrode of a non-aqueous electrolyte battery is produced by mixing an active material with a binder to form an electrode coating-material (mixture), and applying it onto a collector, followed by drying. The battery is produced by superposing and winding up a positive electrode, a separator and a negative electrode, which are obtained in sheets, and encapsulating them together with an electrolytic solution in a battery container.
However, since a stress is imposed on the electrode at the time of winding up or encapsulating the positive electrode, the separator and the negative electrode, unfavorable peeling of the electrode coating layer is generated if the mechanical strength of the electrode is insufficient. This leads to decrease in the yield, and is a factor for higher costs.
In order to solve this problem, the peeling strength of the electrode coating layer has been conventionally increased by increasing the binder composition in the coating layer. However, increase in the binder composition naturally leads to decrease in the composition of the electrode active material in the electrode coating layer, thereby decreasing the battery capacity per unit weight.
Also, for example, in Japanese Laid-open Patent Publication No. 9-237,623/1997, the adhesiveness of the coating layer is enhanced by allowing the amount of the residual N-methylpyrrolidone (NMP) to be 50 to 500 ppm relative to the electrode weight. According to the examples in said Patent Publication, the amount of the residual NMP is adjusted by increasing the period of time for drying immediately after the application of the electrode coating-material. However, when industrial production is considered, the application and drying must inevitably be carried out in successive steps, so that in order to increase the period of time for drying, the amount of application production per hour must be dropped, or otherwise the drying furnace must be made long and large so as to meet the amount of application production. In either case, the productivity falls.
Further, in Japanese Laid-open Patent Publication No. 7-6,752/1995, the electrodes are heated at a temperature not less than the melting point of the binder after the step of pressing the electrodes so as to prevent non-uniform distribution of the binder for improvement of the peeling strength of the coating layer. However, flexibility of the electrodes is deteriorated if a crystalline polymer material having a melting point is used as the binder. As a result, defective cracks may possibly occur in the electrode coating layer in the case of encapsulating the electrode into a battery container by bending it with a small curvature radius in a square-type battery or the like.
DISCLOSURE OF THE INVENTION
Objects of the Invention
Therefore, the object of the present invention is to solve the above-mentioned problem of the prior art, and to provide a method for industrial and simplified production of an electrode for a non-aqueous electrolyte battery without unfavorable peeling of the electrode coating layer while maintaining the flexibility of the electrode by a method other than a drying treatment immediately after application of the electrode coating-material.
SUMMARY OF THE INVENTION
The present inventors have made eager studies and, as a result, found out that an electrode without unfavorable peeling of the coating layer is obtained while maintaining flexibility by using a polymer material substantially having no melting point at not higher than 300° C. as the binder, and carrying out a heating treatment under a specific condition after the electrode coating-material is applied and dried with the use of a polymer material substantially having no melting point at no higher than 300° C. as the binder, thereby completing the present invention. It is understood that the expressions “having no melting point at not higher than 300° C.” and “having no melting point at no higher than 300° C.” have the same meaning as “having a melting point at or below 300° C.”
That is, the present invention is a method of producing an electrode for a non-aqueous electrolyte battery by mixing an electrode active material with a binder to prepare an electrode coating-material, applying the electrode coating-material onto an electrode collector, drying the electrode having the coating layer formed, and then compression-molding the dried electrode, wherein the method comprises using a polymer material substantially having no melting point at not higher than 300° C. as the binder, and carrying out a heating treatment at a temperature not higher than 300° C. for less than 30 hours after the electrode coating-material is applied and dried.
In the present invention, it is preferable that the heating treatment is carried out after the electrode is dried, and thereafter the electrode is compression-molded. Further, the electrode is preferably subjected to the heating treatment in a roll state.
The production method of the electrode of the present invention can be applied to any of a positive electrode and a negative electrode.
DETAILED DESCRIPTION OF THE INVENTION
First, in the method of the present invention, a slurry-like electrode coating-material is prepared by mixing an electrode active material and a binder together with a solvent. Further, in this step, an electrically conductive agent or an additive may possibly be added in accordance with the needs.
As the electrode active material, various materials can be used without particular limitation as long as they are conventionally used as an electrode active material.
As a positive electrode active material, for example, inorganic compounds such as transition metal oxides and transition metal chalcogen compounds containing an alkali metal, conductive polymers such as polyacetylene, poly-p-phenylene, polyphenylenevinylene, polyaniline, polypyrrole, polyazulene, polyphthalocyanine, polythiophene, cross-linked polymers having a disulfide linkage, thionyl chloride and the like may be mentioned. Among these, oxides or chalcogen compounds of transition metals such as cobalt, manganese, molybdenum, vanadium, chromium, iron, copper, titanium and the like are suitable in the case of a secondary battery using a non-aqueous electrolyte solution containing a lithium salt, and Li
x
CoO
2
(0<×≦1.0), Li
x
NiO
2
(0<×≦1.0), Li
x
Co
y
Ni
1−y
O
2
(0<×≦1.0, 0<y≦1.0), Li
1+x
Mn
2−x
O
4
(0≦×≦⅓), Li(M, Mn)
2
O
4
(M═Cr, Co, Al, B) are especially preferable in view of high potential, stability and long life.
Further, as a negative electrode active material, for example, carbonaceous materials, tin oxides and others are used. The carbonaceous materials are not particularly limited, and for example, amorphous carbon, coal cokes, petroleum cokes, vapor growth carbon fibers, hard carbon (slightly graphitizable carbon), polymer carbon, natural graphite, artificial graphite, and others may be mentioned. Among these, those skilled in the art can make a suitable choice in accordance with the intended properties of the battery. When the material is used in a negative electrode of a secondary battery using a non-aqueous electrolyte solution containing an alkali metal salt,

Affiliated with

Also associated with

Rating

Method of producing an electrode does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of producing an electrode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of producing an electrode will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3135124