Coating processes – Electrical product produced
Reexamination Certificate
2000-09-25
2002-11-05
Bareford, Katherine A. (Department: 1762)
Coating processes
Electrical product produced
C029S623100, C029S623500
Reexamination Certificate
active
06475554
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, since a step and equipment for heating are required, the productivity falls in this case as well.
DISCLOSURE OF THE INVENTION
Object 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 by a method other than heating the electrodes or drying immediately after the application.
SUMMARY OF THE INVENTION
The present inventor has made eager studies and, as a result, found out that an electrode without unfavorable peeling of the coating layer is obtained by performing aging for not less than a predetermined period of time after the electrode coating-material is applied onto an electrode collector and dried, thereby completing the present invention.
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 carrying out aging for not less than 18 hours after the electrode is dried.
In the present invention, it is preferable that the aging is carried out after the electrode is dried, and then the electrode is compression-molded.
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<x≦1.0), Li
x
NiO
2
(0<x≦1.0), Li
x
Co
y
Ni
1−y
O
2
(0<x≦1.0, 0<y≦1.0), Li
1+x
Mn
2−x
O
4
(0≦xb ≦{fraction (
1
/
3
)}), 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, PAN-type carbon fibers, pitch-type carbon fibers and vapor growth carbon fibers are preferable, and particularly PAN-type carbon fibers and pitch-type carbon fibers are preferable because of good doping of lithium ions.
The binder in the present invention is not particularly limited, and various binders such as conventionally used crystalline resins and non-crystalline resins can be used. For example, polyacrylonitrile (PAN), polyethylene terephthalate, polyvinylidene fluoride (PVDF), polyvinyl fluoride, fluororubber and others can be used as the binder.
The binder is used usually at an amount of 1 to 40 parts by weight, preferably 1 to 25 parts by weight, especially preferably 1 to 15 parts by weight, with respect to 100 parts by weight of the electrode active material.
The solvent is not particularly limited, and various solvents conventionally used in preparing an electrode coating-material can be used. For example, N-methylpyrrolidone (NMP), methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), cyclohexanone, toluene and others may be mentione
Bareford Katherine A.
Rader & Fishman & Grauer, PLLC
TDK Corporation
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