Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-06-08
2002-04-09
Wu, David W. (Department: 1713)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S217000, C429S208000, C254S109000
Reexamination Certificate
active
06368746
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrochemical device, a molded solid electrolyte and a molded electrode used for the electrochemical device. More specifically, the present invention relates to a molded article holding an electrolyte material and an electrode material, which constitute the electrochemical device by adding a polymer composition to materials which constitute these electrochemical devices, and an electrochemical device constituted by using these molded articles.
BACKGROUND ART
An electrochemical device such as a battery is composed of an electrolyte layer where ion transfer takes place and an electrode layer where donation and acceptance of an electron to an ion are conducted together with the ion transfer. To these electrolyte layer and electrode layer, a polymer composition is added for the following purposes.
(1) Addition to the Electrolyte Layer
In general, an electrolyte is a liquid containing a solvent and a supporting salt dissolved in the solvent, and a container is required to contain the liquid, which makes it difficult to reduce the size and thickness of an electrochemical device. In order to solve the problem, all-solid state electrochemical devices, which use a solid electrolyte instead of a conventional liquid electrolyte, have been researched.
Above all, a lithium battery, which is an electrochemical device, is vigorously researched as a battery which can provide high energy density because lithium is a substance having a small atomic weight and large ionization energy, and has come to be widely used as a power source for a portable appliance.
Also, with the widespread use of lithium batteries, there has been a growing interest in the safety of the batteries because of an increase in internal energy due to an increase in active material content and also because of an increase in organic solvent content, which is a combustible material used in the electrolyte.
As a method of securing the safety of the lithium batteries, it is extremely effective to use a solid electrolyte, which is an incombustible material, instead of an organic solvent electrolyte. Therefore, it is important for a lithium battery to employ a solid electrolyte in order to secure high safety as well as to achieve the above-mentioned reduction in size and thickness.
As the solid electrolytes having lithium ion conductivity used in these batteries, lithium halide, lithium nitride, lithium oxygen acid salt and their derivatives are known. In addition, it is known that amorphous solid electrolytes of sulfides such as Li
2
S—SiS
2
, Li
2
S—P
2
S
5
and Li
2
S—B
2
S
3
having lithium ion conductivity, and lithium ion conductive solid electrolytes made by doping lithium halide such as LiI or a lithium salt such as Li
3
PO
4
to these glasses show high ionic conductivity of 10
−4
to 10
−3
S/cm or higher.
Unlike these inorganic solid electrolytes, polymer solid electrolytes comprising organic materials are obtained by evaporating a solvent from a solution containing a lithium salt and an organic polymer compound. This polymer solid electrolyte has excellent processibility in that it is formed into a thin film easier than an inorganic solid electrolyte and that the resultant solid electrolyte thin film has flexibility.
Recently, as a solid electrolyte having flexibility or rubber elasticity, a novel solid electrolyte named polymer in salt type compring an inorganic salt and a polymer compound, which has lithium ion conductivity of extremely higher density than the above-mentioned polymer solid electrolyte has been suggested by C. A. Angell et al. (C. A. Angell, C. Liu and E. Sanchez, Nature, vol. 632, (1993) 137).
In an electrochemical device using a liquid electrolyte, too, a porous polymer composition is usually used as a separator in the electrolyte layer. The separator is required to prevent an electric contact between the electrodes mechanically, to have excellent liquid retentivity for retaining the liquid electrolyte and to be chemically stable in the electrochemical device. Since it is used in contact with the electrodes, the separator is further required to be electrochemically stable.
(2) Addition to the Electrode Layer
The electrode is constituted by molding an electrode active material and by connecting it to a current collector. When the electrode active material is molded merely by a pressure molding method, the aggregation force between electrode active material particles is mainly van der Waals only. In an ordinary electrochemical device, however, a liquid is used as the electrolyte and, therefore, when the molded electrode constituted by the pressure molding method only is immersed in a liquid electrolyte, the liquid molecules are adsorbed on the surface of the electrode active material particles. As a result, the aggregation force between the active material particles decreases and the electrode active material particles drop off from the molded electrode into the liquid electrolyte, making it impossible to keep the shape of the molded electrode. Therefore, in order to improve the molding property of the electrode, a polymer composition is generally added as a binder to t he molded electrode.
The polymer composition is added to the electrolyte layer or electrode layer of an electrochemical device for the above-mentioned purposes; however, these prior arts have the following problems.
(3) Problems Involved in the Addition to the Electrolyte Layer
The above-mentioned inorganic solid electrolyte comprises ceramic or glass, and in applying to a battery, it is generally used as a pellet obtained by pressure molding pulverized solid electrolyte powder. However, there is a problem that the obtained pellet has poor workability due to the hardness and brittleness, thereby preventing the electrolyte layer from decreasing in the thickness and increasing in the area.
On the other hand, the solid electrolyte comprising organic materials has low ionic conductivity of 10
−4
S/cm or less at room temperature, which is not sufficient as a practical lithium battery electrolyte. In order to solve this problem, a polymer solid electrolyte having ionic conductivity improved by adding a plasticizer has been proposed. However, a plasticizer is inherently combustible, which reversely causes a problem that adding the plasticizer decreases the transport number of lithium ions or decreases reactivity with a lithium anode. Whether a plasticizer is added or not, it is hard to say that these organic solid electrolytes have sufficient performance as the lithium battery electrolytes.
The above-mentioned “polymer in salt” type solid electrolyte has low conductivity not exceeding 10
−4
S/cm, so it is impossible to say that the electrolyte has sufficient ionic conductivity as the lithium battery electrolyte. When an ambient temperature molten salt (a salt in a liquid state at room temperature) such as AlCl
3
—LiBr—LiClO
4
is used as an inorganic salt, it shows high ionic conductivity, but is likely to cause an electrochemical reduction of aluminum, so it cannot be said to be suitable for the lithium battery electrolyte.
(4) Problems Involved in the Addition to the Electrode Layer
As mentioned above, a molded electrode is constituted by adding a polymer composition as a binder to an electrode active material. In general, a polymer compound is electrically insulating and likely to disturb ion transfer, and interferes electrochemical reactions caused on the electrode/electrolyte interface and ion dispersion in an electrode. Consequently, there is a problem that when the mixing ratio of the polymer compound is increased to enhance the processibility, operating performance of the electrochemical device tends to decrease.
The molded electrode is obtained as follows. That is, a slurry is obtained by mixing a mixture of an electrode active material, a binder and an electron conductive material added when needed to improve the electron conductivity in an electrode in a dispersing medium. Then, the slurry is filled into or applied onto a current collector and the disper
Iwamoto Kazuya
Kondo Shigeo
Masaka Fusazumi
Takada Kazunori
Takeuchi Yasumasa
Egwim K. C.
Matsushita Electric - Industrial Co., Ltd.
McDERMOTT, WILL & EMERY
Wu David W.
LandOfFree
Molded solid electrolyte, molded electrode and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Molded solid electrolyte, molded electrode and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Molded solid electrolyte, molded electrode and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2823900