Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1998-09-08
2001-02-20
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S317000, C361S525000, C558S265000
Reexamination Certificate
active
06190805
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a solid polymer electrolyte comprising a polymer compound containing a poly- or oligo-carbonate group as a main component, and an electrolyte salt, which is useful for various electrochemical elements, and a production process thereof, a battery using the solid polymer electrolyte and a production process thereof, and an electric double layer capacitor using the solid polymer electrolyte and a production method thereof.
BACKGROUND OF THE INVENTION
To keep up with the trend in the ionics field toward downsizing and entirely solid formation, attempts are being aggressively made to apply an entirely solid primary battery, secondary battery or electric double layer capacitor using a solid electrolyte to electrochemical elements, as a new ion conductor which can take the place of conventional electrolytic solutions.
More specifically, electrochemical elements using a conventional electrolytic solution are deficient in the long-term reliability because liquid leakage outside the component or elution of the electrode active material is readily caused. However, products using a solid electrolyte are free of such a problem and can be easily formed to have a small thickness. Furthermore, the solid electrolyte has excellent heat resistance and is advantageous also in the manufacturing process of a product such as a battery.
In particular, when a solid polymer electrolyte mainly comprising a polymer compound is used, the battery can have increased flexibility as compared with those using an inorganic material and accordingly, can be formed into various shapes. However, batteries heretofore investigated have a problem that due to low ion conductivity of the solid polymer electrolyte, the takeout current is small.
In recent years, many studies have been made on lithium secondary batteries using a metal oxide or metal sulfide such as LiCoO
2
, LiNiO
2
, LiMnO
2
and MoS
2
for the positive electrode, and lithium, lithium alloy, a carbon material, inorganic compound or polymer compound capable of occluding and releasing lithium ion for the negative electrode. For example,
J. of Electrochem. Soc
., vol. 138 (No. 3), page 665 (1991) reports a battery using MnO
2
or NiO
2
for the positive electrode. This is high in the capacity per weight or per volume and drawing attention.
Further, an electric double layer capacitor comprising polarizable electrodes formed of a carbon material having a large specific area, such as activated carbon or carbon black, having disposed therebetween an ion conductive solution is often used in these days as a memory backup power source. For example,
Kino Zairyo
(
Functional Materials
), page 33, (February, 1989) describes a capacitor using carbon-base polarizable electrodes and an organic electrolytic solution; and 13
th Electrochemical Society Meeting Atlanta Ga
., No. 18 (May, 1988) describes an electric double layer capacitor using an aqueous sulfuric acid solution.
Further, JP-A-63-244570 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a capacitor using Rb
2
Cu
3
I
3
Cl
7
having high electrical conductivity as an inorganic solid electrolyte.
However, the battery or electric double layer capacitor using an existing electrolytic solution is deficient in the long-term use or reliability because liquid leakage outside the battery or capacitor is readily caused under an abnormal condition such as when the battery or capacitor is used for a long period of time or a high voltage is applied. On the other hand, the battery or electric double layer capacitor using a conventional inorganic ion conductive material has a problem that the ion conductive material is low in the decomposition voltage and accordingly, the output voltage is low, or has a problem in the production process because an interface between the electrolyte and the electrode is difficult to form.
JP-A-4-253771 proposes to use a polyphosphazene-base polymer compound as an ion conductive material of a battery or electric double layer capacitor. The battery or electric double layer capacitor using a solid ion conductive material mainly comprising such a polymer compound is advantageous in that the output voltage is high as compared with those using an inorganic ion conductive material and it can be formed into various shapes and easily sealed. However, in this case, the ion conductivity of the solid polymer electrolyte is not sufficiently high and it is approximately from 10
−4
to 10
−6
S/cm, as a result, the takeout current is disadvantageously small. Furthermore, in assembling a solid electrolyte together with polarizable electrodes in a capacitor, it is difficult to uniformly compound the solid electrolyte with the carbon material having a large specific area because the materials mixed are both a solid.
The solid polymer electrolytes under general investigations are improved in the ion conductivity up to approximately from 10
−4
to 10
−5
S/cm at room temperature, however, this still stays in a level lower by two figures than that of the liquid ion conductive material. Further, at low temperatures of 0° C. or less, the ion conductivity generally lowers to an extreme extent. Furthermore, when the solid electrolyte is compounded and assembled with an electrode of an element such as a battery or electric double layer capacitor or when the solid electrolyte is formed into a thin film and assembled in an element such as a battery or electric double layer capacitor, difficult techniques are necessary for the working of compounding or continuously contacting the solid polymer electrolyte with an electrode, thus, a problem is also present in the process of producing an element.
As an example of the solid polymer electrolyte,
Br. Polym. J
., Vol. 319, page 137 (1975) reports that a composite material of a polyethylene oxide with an inorganic alkali metal salt exhibits ion conductivity, but the ion conductivity thereof at room temperature is as low as 10
−7
S/cm.
Many reports have been issued in recent years stating that a comb-type polymer having introduced into the side chain thereof oligooxyethylene is intensified in the thermal mobility of oxyethylene chain which undertakes the ion conductivity, and thereby improved in the ion conductivity.
For example,
J. Phys. Chem
., Vol. 89, page 987 (1984) describes an example where oligooxyethylene is added to the side chain of polymethacrylic acid and an alkali metal salt is compounded thereto. Further,
J. Am. Chem. Soc
., Vol. 106, page 6854 (1984) describes polyphosphazene having an oligooxyethylene side chain, compounded with an alkali metal salt, however, the ion conductivity is about 10
−5
S/cm and still insufficient.
U.S. Pat. No. 4,357,401 reports that a solid polymer electrolyte comprising a salt ionizable with a cross-linked polymer having a hetero atom is reduced in the crystallinity, has a low glass transition point and is improved in the ion conductivity, but the ion conductivity is about 10
−5
S/cm and still insufficient.
J. Appl. Electrochem
., Vol. 5, pp. 63-69 (1975) reports that a so-called polymer gel electrolyte obtained by adding a solvent and an electrolyte to a cross-linked polymer compound, such as polyacrylonitrile or polyvinylidene fluoride gel, has a high ion conductivity. Further, JP-B-58-36828 (the term “JP-B” as used herein means an “examined Japanese patent publication”) reports that a polymer compound gel electrolyte similarly obtained by adding a solvent and an electrolyte to a polymethacrylic acid alkyl ester has a high ion conductivity.
However, despite the high ion conductivity, these polymer gel electrolytes are disadvantageous in that due to the fluidity imparted, they cannot be handled as a complete solid, have poor film strength or film formability, readily cause short circuit when applied to an electric double layer capacitor or a battery, and have a problem in view of sealing similar to the case of using a liquid ion conductive material.
U.S. Pat. No. 4,792,504 propo
Naijo Shuichi
Nishioka Ayako
Nishioka Masaaki
Ohkubo Takashi
Takeuchi Masataka
Kalafut Stephen
Showa Denko Kabushiki Kaisha
Sughrue, Mion, Zinn Macpeak & Seas, PLLC.
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