Compositions – Electrolytes for electrical devices
Reexamination Certificate
2001-08-22
2003-09-30
Koslow, C. Melissa (Department: 1755)
Compositions
Electrolytes for electrical devices
C252S399000, C429S199000, C429S200000, C429S306000, C429S324000, C429S347000, C136S252000, C136S243000, C136S254000, C136S263000
Reexamination Certificate
active
06627099
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel electrolyte composition and an electrochemical battery using the same. More particularly, the present invention relates to a non-aqueous secondary battery and a photoelectric chemical battery.
2. Description of the Related Art
The electrolyte used in an electrochemical battery such as a non-aqueous secondary battery or a dye sensitized battery, contains ions which are selected in accordance with the purpose of the battery. The electrolyte is a medium which functions to transport these ions between electrodes, and this function is referred to as “ion conductivity”. For example, a lithium secondary battery, which is a typical non-aqueous secondary battery, has a problem pertaining to the transportation of a lithium ion, while a dye-sensitizing solar battery has a problem pertaining to the conductivity of an iodide ion or an iodide trimer ion. In such batteries, generally, as electrolytes, there are used many solution systems having high ion conductivity. However, a problem arises that, due to depletion or leakage of a solvent when it is contained in a battery, durability of the battery may deteriorate. Further, in the lithium secondary battery, since a metallic container must be used to seal a solution therein, the weight of a battery becomes heavier, and it becomes difficult to provide a battery which has a high degree of freedom with respect to configuration.
Recently, in order to overcome such drawbacks concerning a solution system electrolyte, there have been proposed a variety of electrolytes. For example, a so-called gel electrolyte in which the solution system electrolyte is soaked in a polymer matrix is more advantageous as compared to the solution system electrolyte in that deterioration of ion conductivity of the gel electrolyte is reduced so that battery performance does not deteriorate. However, the gel electrolyte is not able to completely inhibit volatilization of a solvent, thereby can not completely solve problems concerning the solution system electrolyte. Further, a polymer electrolyte having a salt dissolved in a polymer such as a polyethylene oxide was expected to solve such a problem described above. However, ion conductivity of the polymer electrolyte is still insufficient. On the other hand, an imidazolium salt or a pyridinium salt having BF
4−
or (CF
3
SO
2
)
2
N— and the like as a counter anion, is a room temperature molten salt which is liquefied at room temperature, and these salts have been proposed as electrolytes for a lithium ionic battery. However, the mechanical strength and ion conductivity of the electrolyte have an inverse relationship with each other. Therefore, when the mechanical strength is increased by increasing the viscosity of the molten salt itself or by including a polymer therein, ion conductivity of the electrolyte may deteriorate. Further, in such an electrolyte described above, ion conductivity largely depends on temperature, and is insufficient particularly at a low temperature.
In solar power generation in which light energy is converted to electric energy, a single crystal silicon solar battery, a polycrystalline silicon solar battery, an amorphous silicon solar battery, and a compound solar battery such as cadmium telluride or indium copper selenide have been used for practical purposes or for research and development. However, in order to use such solar batteries in general, problems with respect to manufacturing cost, availability of a raw material, duration of an energy payback time, and the like must be solved. On the other hand, there has been proposed a large number of solar batteries in which organic materials are used to increase size or reduce cost. However, a problem arises that energy conversion efficiency is low and durability is poor.
Under such circumstances, in “Nature” (volume No. 353, pages 737 to 740, in 1991), U.S. Pat. No. 4,927,721, and the like, there are disclosed technologies regarding a photoelectric conversion element which uses an oxide semiconductor which was sensitized by a dye (abbreviated to a “dye-sensitized photoelectric conversion element” hereinafter) and a photoelectric chemical battery using the same. The batteries disclosed above are formed by a photoelectric conversion element which functions as a negative electrode, a charge transport layer, and a counter electrode. The aforementioned photoelectric conversion element is formed by an electric conductive support and a photosensitive layer, which photosensitive layer includes a semiconductor having a dye adsorbed on the surface thereof. The aforementioned charge transport layer is formed by an oxidation reductant, which is responsible for charge transportation between a negative electrode and a counter (positive) electrode. A battery made by this method is favorable in that they are inexpensive and they can provide a relatively high energy conversion efficiency (i.e., photoelectric conversion efficiency). However, because an aqueous solution (i.e., electrolyte solution) using a salt such as potassium iodide as an electrolyte is used as a charge transport layer, long-term use of this battery causes the electrolyte to transpire and thus become depleted, thereby causing a problem in that the photoelectric conversion efficiency deteriorates noticeably or the battery no longer functions as a battery.
In order to solve this problem, WO95/18456 discloses a method in which depletion of an electrolyte solution is prevented by using an imidazolium salt i.e., a low molten compound as an electrolyte. Through this method, since water or an organic solvent which has been conventionally used as a solvent for an electrolyte becomes unnecessary or since it is sufficient to use only a small amount thereof, durability of the electrolyte is improved. However, the durability is still insufficient for practical use. Further, when the concentration of the imidazolium salt is increased, there arise problems in that the viscosity increases, the charge transport performance deteriorates, and the photoelectric conversion efficiency thereby decreases. Moreover, although there has been provided a method using a triazolium salt as an electrolyte, there arises a problem similar to that of the imidazolium salt.
SUMMARY OF THE INVENTION
In a conventional electrochemical battery, when an electrolyte composition containing a low molecular solvent was used, there was a problem of durability in that the solvent volatilizes or leaks to thereby deteriorate battery performance. On the other hand, when a salt-based electrolyte which is liquefied at room temperature i.e., a so-called molten salt electrolyte was used, since this electrolyte does not contain a low boiling point compound, it is effective in preventing deterioration of the battery performance due to volatilization. However, there is a drawback in that, since viscosity of the electrolyte is generally high, charge transport performance thereof is low.
In view of the aforementioned problems, an object of the present invention is to provide an electrolyte composition that is excellent in durability and charge transport performance. Further, another object of the present invention is to provide an electrochemical battery in which deterioration of the battery performance with time is minimized.
Means for solving the aforementioned problems are described below:
A first aspect of the present invention is an electrolyte composition that includes a salt therein, the salt comprising: an anion which contains a mesogen group and an alkyl or alkenyl group having 6 carbons or more in the structure thereof; and an organic or inorganic cation.
A second aspect of the present invention is: an electrolyte composition that includes a salt therein, the salt comprising: an anion which contains a mesogen group, and an alkyl or alkenyl group having 6 carbons or more in the structure thereof; and an organic or inorganic cation, wherein the mesogen group is represented by the following formula (1):
wherein Y
11
represents a bivalent 4 to 7-m
Ono Michio
Qian Chang-yi
Wariishi Koji
Yasuda Takayasu
Burns Doane , Swecker, Mathis LLP
Fuji Photo Film Co. , Ltd.
Koslow C. Melissa
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