Compositions – Compositions containing a single chemical reactant or plural... – Organic reactant
Reexamination Certificate
2001-12-03
2003-11-25
Egwim, Kelechi (Department: 1713)
Compositions
Compositions containing a single chemical reactant or plural...
Organic reactant
C427S189000, C427S190000, C427S194000, C427S198000, C427S217000, C524S543000
Reexamination Certificate
active
06652773
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polymer dispersion composition obtained by dispersing a polymer in an organic dispersion medium. The polymer dispersion composition is successfully usable as a binder composition for batteries. Accordingly, the present invention also relates to a slurry composition for batteries using said polymer dispersion composition as a binder composition for batteries, and to an electrode and a battery using the same.
BACKGROUND ART
An elastomer is a soft polymer having rubber elasticity of which glass transition temperature is 30° C. or below. Such elastomers are in use in various fields.
An elastomer is used for forming a uniform film by the procedure of (1) melting, followed by coating, (2) forming a uniform solution by dissolution in an organic solvent, followed by coating, (3) forming a stable dispersion in an aqueous solvent by the use of a surfactant, followed by coating, etc. Although JP-A, 6-179707 proposes a method of dispersing an elastomer in an aqueous or organic solvent without using surfactant, the examples presented in the specification thereof are limited to those using an aqueous solvent, and the films formed by the use of an organic solvent are considered a homogeneous films. Thus, there is known no case of using an elastomer dispersion composition prepared by dispersing an elastomer in an organic dispersion medium for formation of a heterogeneous film having a high gel content or for a general binder.
A battery has positive and negative electrodes as the constituent elements thereof. An electrode is constituted of a variety of elements including an active material participating in electrochemical reaction, an electrode base, electroconductive particles as optional constituents, etc. An electrode is prepared by mixing an active material, etc. with a binder composition, etc. to form a slurry composition for batteries, coating the slurry composition onto an electrode base, and drying it. A slurry composition for batteries is prepared by adding an active material to a binder composition comprising a binder polymer and a solvent or a dispersion medium.
The prior binder compositions for batteries are classified into those of organic solvent type and those of aqueous solvent type. Most of the conventional organic solvent type of binder compositions for batteries are solution type binder compositions prepared by uniformly dissolving polyvinylidene fluoride in N-methylpyrrolidone which is a polar organic solvent (for example, see: JP-A, 4-249860), and there is known no case of using an elastomer dispersion composition prepared by dispersing an elastomer in an organic dispersion medium as a binder composition for batteries.
The prior organic solvent type binder compositions are free from the faults of the aqueous binder compositions mentioned below, because they are of organic solvent type. However, the uniform film formed from the homogeneous solution comes to cover the whole surface of electrode active material, which is undesirable under the present conditions of matters where enhancement of the capacity of battery is desired, because such a uniform film decreases the surface area of active material coming into a direct contact with electrolyte. It is desired to enlarge the proportion of active material contributing to electric capacity of active material, namely to enlarge the surface area of active material coming into contact with electrolyte.
As aqueous binder compositions, there have been proposed those prepared by adding carboxymethyl cellulose as a thickener to an aqueous dispersion of styrene-butadiene copolymer rubber latex prepared by emulsion polymerization using a surfactant (for example, JP-A, 4-342966, JP-A, 5-21068, JP-A, 5-74461, etc.). This type of binder compositions have a problem that, when used in a lithium ion secondary battery or the like, the contact with water causes formation of hydroxyl groups linked to active material surface which can exercise an influence of lowering the initial capacity. Further, there is a problem that, in a non-aqueous battery of lithium type using a non-aqueous electrolyte, the contact with water must be avoided as possible from the viewpoint of improving the efficiency of manufacture, even though the battery manufacturing process may include a drying step.
The present inventors have succeeded in preparing a polymer dispersion composition by dispersing a specified polymer in a specified organic dispersion medium, and have found that the polymer dispersion composition thus obtained can successfully be used as a binder composition for batteries. Based on the finding, the present invention has been accomplished.
DISCLOSURE OF THE INVENTION
(Polymer Dispersion Composition)
Accordingly, an object of the present invention is to provide a polymer dispersion composition wherein a specified polymer is dispersed in a specified organic dispersion medium, to use the polymer dispersion composition as, for instance, a binder composition for batteries, to suppress the deteriorating quality of active material caused by water, to make it possible to fix an electrode active material on an electrode in a partially exposed state without coating the whole surface of the electrode active material, and thereby to make small the extent of damage in the function of active material. It is a further object of the invention to fix a large quantity of active material on an electrode base by the use of such a binder composition for batteries and thereby to provide a battery having a high initial capacity and prevent the release of active material from electrode base even after repeated charge and discharge cycle.
BEST EMBODIMENT FOR CARRYING OUT THE INVENTION
Thus, according to the present invention, there are provided a polymer dispersion composition obtained by dispersing a polymer having a gel content of 50% or more in an organic dispersion medium having a boiling point of 80° C. or above at 760 mmHg, a slurry composition for batteries obtained by mixing said composition with an electrode active material, an electrode obtained by coating said slurry composition for batteries onto the surface of a battery base and then removing the organic dispersion medium, and a battery using said electrode.
The organic dispersion medium used in the present invention has a boiling point of 80° C. or above, preferably 100° C. or above, at 760 mmHg. When used as a binder composition for batteries, the organic dispersion medium preferably has a boiling point of 150° C. or below at 760 mmHg and a boiling point of 300° C. or below at 760 mmHg, because it is necessary to dry an electrode base without deterioration thereof. If the boiling point at 760 mmHg is lower then 80° C., the drying progresses too rapidly so that coating of the electrode base is difficult to carry out; and the polymer migrates and is concentrated into the surface of electrode base during the drying step to cause problems such as deterioration of film strength, decrease of binding force between electrode active material particles, etc. These problems arise especially when the organic dispersion medium is an alcohol or a ketone of which boiling point is lower than 80° C., such as ethyl alcohol.
As concrete examples of the organic dispersion medium, there can be referred to a variety of polar and non-polar dispersion mediums including aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene and the like; aliphatic hydrocarbons such as heptane, octane, nonane, decane and the like; alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, ethylcyclohexane and the like; ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, cycloheptanone and the like; cyclic and acyclic amides such as dimethylformamide, N-methyl-pyrrolidone and the like; alcohols such as butyl alcohol, amyl alcohol, hexyl alcohol and the like; esters such as methyl lactate, ethyl lactate, butyl lactate, butyl acetate, methyl benzoate and the like; etc. In a case where the composition is used as a binder composition for
Imai Keiko
Inoue Toshihiro
Maeda Koichiro
Yamamoto Haruhisa
Armstrong Westerman & Hattori, LLP
Egwim Kelechi
Nippon Zeon Co. Ltd.
LandOfFree
High gel-content polymer dispersed in a high-boiling organic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High gel-content polymer dispersed in a high-boiling organic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High gel-content polymer dispersed in a high-boiling organic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3183208