Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-11-21
2003-06-10
Weiner, Laura (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S217000, C429S233000, C429S245000, C429S304000, C252S062200
Reexamination Certificate
active
06576372
ABSTRACT:
TECHNICAL FIELD
The present invention relates to polyurethane compounds which can be utilized as electrochemical materials, including electrolytes for various types of secondary cells and adhesive binders for battery active materials. The invention relates also to binder resins, to ion-conductive polymer electrolyte compositions composed primarily of ion-conductive salts in combination with polyelectrolyte-providing polymers made of such polymeric compounds, and to secondary cells.
BACKGROUND ART
Electrolytes used in secondary cells and other electronic and electrical devices have until now been substances that are liquid at or above room temperature, such as water, propylene carbonate, ethylene carbonate and tetrahydrofuran. In lithium ion cells in particular, use is commonly made of organic liquid electrolytes which tend to evaporate, ignite, and burn rather easily. To ensure long-term stability, it is necessary to increase the airtightness of the container by using a metal can as the cell enclosure. Failure to do so leaves open the possibility that the electrolyte will evaporate and the vaporized electrolyte will ignite and cause a fire.
Hence, there has been a considerable rise in the eight of electrical and electronic devices which use organic liquid electrolytes. Moreover, in the manufacture of thin, large-area stacked cells, the process of injecting electrolyte solution is quite difficult. Another problem has been a shortened cycle life due to the drop off of battery active material and dendrite deposition.
By contrast, the use of polymeric compounds as the electrolyte provides electrolytes which have a very low volatility and are not prone to evaporation. Such polymer electrolytes include solid electrolytes composed of, for example, polyethylene oxide and a lithium salt.
However, these polymer electrolytes have a low conductivity compared with liquid electrolytes. Solid electrolytes composed of polyethylene oxide having branched chains have been proposed in order to enhance the conductivity, but the conductivity in such a case is still less than 10
−5
S/cm, which is rather low. In addition, the closeness of contact between the electrodes and the electrolyte is difficult to maintain. The unfortunate result is a large interfacial impedance, leading to an increase in polarization.
Moreover, a major problem encountered when polymer electrolytes are used to manufacture film-type batteries concerns adhesion between the positive and negative electrodes and the polymer electrolyte.
Specifically, film-type batteries which use solid polymer electrolytes generally have a positive electrode/solid electrolyte
egative electrode construction. Unlike cylindrical batteries in which the positive electrode/solid electrolyte
egative electrode composite is coiled and placed in a can, the absence of a coiling pressure in film-type batteries means that pressure is not applied between the positive electrode and the solid electrolyte and between the solid electrolyte and the negative electrode, allowing the solid electrolyte to separate readily from the positive electrode and the negative electrode. Thus, the solid electrolyte disposed between the positive electrode and the negative electrode, in addition to its role as an electrolyte, must also have the ability to strongly bond the positive and negative electrodes. That is, it must have tackiness and adhesiveness.
In addition, to lower the interfacial resistance between the electrodes and the solid electrolyte, the same electrolyte polymer as that used in the solid electrolyte is sometimes employed as a binder resin (electrode binder). In such cases, the electrolyte polymer which serves also as a binder resin must have the ability to bond a powdery battery active material; that is, it must have tackiness in addition to ionic conductivity.
The solid polymer electrolytes that have hitherto been reported in the literature are lacking not only in sufficient ionic conductivity, but also in tacky and adhesive properties. Hence, a need has been felt for further improvement.
DISCLOSURE OF THE INVENTION
The present invention was conceived in light of these circumstances. One object of the invention is to provide a polyurethane compound in which a substituent having a large dipole moment has been introduced onto the polyurethane molecule and which improves the closeness of contact between the electrodes and the electrolyte, thus enabling to obtain an interfacial impedance comparable to that of an electrolyte solution, while maintaining a high dielectric constant and the ability to dissolve an ion conductive salt to a high concentration. Another object of the invention is to provide a binder resin composed of the same polymeric compound; an ion-conductive polymer electrolyte composition having a high ionic conductivity and a high bond strength which is composed primarily of an ion-conductive salt and a polyelectrolyte-providing polymer made of the same polymeric compound: and a secondary cell comprising the binder resin and the ion-conductive polymer electrolyte composition.
Conducting extensive investigations in order to achieve these aims, the inventors have made the following discoveries.
(1) An ion-conductive solid polymer electrolyte has a considerably high concentration of ion-conductive metal salt, and ion association readily arises in a low-dielectric-constant polymer matrix, resulting in a decline in conductivity due to ion association.
(2) In such cases, introducing onto the polymer a substituent having a large dipole moment so as to increase the polarity of the matrix discourages ion association, thereby enhancing ionic conductivity.
(3) Introducing a substituent having a large dipole moment onto a polyurethane compound dramatically improves adhesion and tackiness.
Pursuing investigations even further based on these findings, the inventors have found also that polyurethane compounds which have been prepared by reacting an excess of an isocyanate compound with a polyol compound to form a polyurethane compound and reacting the hydroxyl group of an alcohol compound bearing a substituent having a large dipole moment with some or all of the remaining isocyanate groups on the polyurethane compound, and in which the substituent having a large dipole moment is coupled to the polyurethane compound through a NHCOO linkage, have a high dielectric constant, the ability to dissolve the ion-conductive salt to a high concentration and excellent adhesive properties, thus affording close contact between the electrodes and the electrolyte as well as an interfacial impedance comparable with that of electrolyte solutions. The inventors have additionally discovered that binder resins composed of such polymeric compounds have the ability to bond powdery battery active materials, and that ion-conductive polymer electrolyte compositions composed primarily of an ion-conductive salt and a polyelectrolyte-providing polymer made of the above polymeric compound have a high ionic conductivity and a high tackiness. Hence, it has become apparent that, in addition to their role as excellent electrolytes, such polymer electrolyte compositions also serve to firmly bond the positive and negative electrodes, and are thus ideally suited for use in film-type batteries and other kinds of secondary cells.
Accordingly, the present invention provides:
(1) a polyurethane compound prepared by reacting an excess of an isocyanate compound with a polyol compound to form a polyurethane compound and reacting the hydroxyl group of an alcohol compound bearing a substituent having a large dipole moment with some or all of the remaining isocyanate groups on the polyurethane compound, wherein the substituent having a large dipole moment is coupled to the polyurethane compound through a NHCOO linkage;
(2) a binder resin comprising the above polyurethane compound;
(3) an ion-conductive polymer electrolyte composition composed primarily of an ion-conductive salt and the above polyurethane compound;
(4) the above composition which is obtained by reacting (A) an isocyanate compound, (B) a po
Hata Kimiyo
Sato Takaya
Birch & Stewart Kolasch & Birch, LLP
Nisshinbo Industries Inc.
Weiner Laura
LandOfFree
Polymer compound, binder resin, composition for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polymer compound, binder resin, composition for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polymer compound, binder resin, composition for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3138398