Non-aqueous electrolyte electric double-layer capacitor

Details Non-aqueous electrolyte electric double-layer capacitor Non-aqueous electrolyte electric double-layer capacitor

2000-11-09

2002-10-22

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Double layer electrolytic capacitor

C361S503000, C361S504000, C361S508000, C361S512000, C029S025030

Reexamination Certificate

active

06469888

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-aqueous electrolyte electric double-layer capacitor appropriately used in back-up power supplies, auxiliary power supplies and the like, and various types of energy reserves.
2. Description of the Related Art
Non-aqueous electrolyte electric double-layer capacitors are capacitors that use an electric double-layer formed between a polarizable electrode and an electrolyte. These capacitors were first developed and produced in the 1970s, underwent a period akin to early infancy in the 1980s, and experienced a period of growth and development beginning in the 1990s.
Non-aqueous electrolyte electric double-layer capacitors differ from batteries in that the charge/discharge cycle of a non-aqueous electrolyte electric double-layer capacitor is a cycle in which ions are electrically adsorbed from an electrolyte on an electrode surface, while the charge/discharge cycle of a battery is an oxidation-reduction reaction cycle accompanied by a mass transfer. In comparison with batteries, non-aqueous electrolyte electric double-layer capacitors have the following advantages: the capacitors have excellent instantaneous charge/discharge properties which show virtually no deterioration even when charge/discharge is repeated; because there is no charge/discharge overvoltage at the time of charge/discharge, the capacitors suffice as simple and inexpensive electrical circuits; the remaining capacity can be easily understood; the capacitors have durable temperature properties in temperature conditions within a range of −30° C. to 90° C.; and the capacitors are non-polluting. For these reasons, non-aqueous electrolyte electric double-layer capacitors have been spotlighted in recent years as an environmentally sound, new energy reserve product.
A non-aqueous electrolyte electric double-layer capacitor is an energy reserve device having a positive and negative polarizable electrode and an electrolyte. In a contact surface between the polarizable electrode and the electrolyte, positive and electric charges oppose one another in an array with an extremely short distance separating the charges to form an electric double-layer. Because the electrolyte serves as an ion source for the purpose of forming the electric double-layer, similar to the polarizable electrode, the electrolyte is an important substance that controls the basic properties of the energy reserve device.
Conventionally, aqueous electrolytes, non-aqueous electrolytes, solid electrolytes and the like have been known as the aforementioned electrolyte. However, from the standpoint of improving the energy density of a non-aqueous electrolyte electric double-layer capacitor, non-aqueous electrolytes in particular have garnered attention among these electrolytes because a high operational voltage can be set. Application of non-aqueous electrolytes has therefore progressed.
At present, non-aqueous electrolytes in which a solute (supporting electrolyte) such as (C
2
H
5
)
4
P·BF
4
or (C
2
H
5
)
4
N·BF
4
or the like has been dissolved in an organic solvent having a high permittivity such as a carbonate (e.g., ethyl carbonate, propylene carbonate and the like), gamma butyrolactone or the like are being applied.
However, because the flash point of the solvent included in these non-aqueous electrolytes is low, there has been the problem that when the non-aqueous electrolyte electric double-layer capacitor is ignited by heat or the like, the non-aqueous electrolyte catches fire, flames spread over the surface of the non-aqueous electrolyte, and the risk of danger is therefore high. There has also been the problem that vaporization and decomposition of the non-aqueous electrolyte due; to heat or the like can generate gas which causes the non-aqueous electrolyte electric double-layer capacitor to burst or ignite, whereby the non-aqueous electrolyte catches fire, flames spread over the surface of the non-aqueous electrolyte, and the risk of danger is therefore high.
Attendant to the application of non-aqueous electrolyte electric double-layer capacitors in recent years, expectations have come to be placed on the development of electric automobiles, hybrid cars and the like, and the demand for the safety of non-aqueous electrolyte electric double-layer capacitors continues to escalate each day.
In the midst of such circumstances, development has been anticipated of non-aqueous electrolyte electric double-layer capacitors whose safety is fundamentally high regardless of safety measures such as providing auxiliary parts like safety valves, which have respective properties such as safety, charge/discharge amount and low internal resistance which are equally as superior as those of conventional non-aqueous electrolyte electric double-layer capacitors, which have excellent resistance to flammability, excellent self-extinguishability or incombustibility, excellent resistance to deterioration, excellent long-term stability, are electrochemically safe and easy to manufacture.
SUMMARY OF THE INVENTION
In response to such demands, the present invention was devised in order to solve the various problems occurring in the conventional art and achieve the following objects.
A first object of the present invention is to provide a non-aqueous electrolyte electric double-layer capacitor in which there is no danger of being ignited, which exhibits excellent safety as a result of there being no danger of bursting or catching flame in the event of a short-circuit, which maintains sufficient electrical conductivity, in which the surface resistance of the non-aqueous electrolyte is low, and which has excellent properties at low temperatures.
A second object of the present invention is to provide a non-aqueous electrolyte electric double-layer capacitor able to maintain safety and long-term stability required as a capacitor, which has excellent self-extinguishability or incombustibility, is electrochemically safe and resistant to deterioration, in which the surface resistance of the non-aqueous electrolyte is low, and which has excellent properties at low temperatures.
A third object of the present invention is to provide a non-aqueous electrolyte electric double-layer capacitor which maintains respective properties required as a non-aqueous electrolyte electric double-layer capacitor such as low internal resistance, has excellent self-extinguishability or incombustibility and is resistant to deterioration, in which the surface resistance of the non-aqueous electrolyte is low, and which has excellent properties at low temperatures.
A fourth object of the present invention is to provide a non-aqueous electrolyte electric double-layer capacitor which maintains respective properties required as a non-aqueous electrolyte electric double-layer capacitor such as low internal resistance, has excellent self-extinguishability or incombustibility and is resistant to deterioration, in which the surface resistance of the non-aqueous electrolyte is low, and which by using only a phosphazene derivative as a solvent exhibits excellent long-term stability, can be easily manufactured and has excellent properties at low temperatures.
A first aspect of the non-aqueous electrolyte electric double-layer capacitor of the present invention for the purpose of achieving the first object is a non-aqueous electrolyte electric double-layer capacitor comprising a non-aqueous electrolyte having a supporting electrolyte and a phosphazene derivative, and a positive electrode and a negative electrode.
A second aspect of the non-aqueous electrolyte electric double-layer capacitor of the present invention for the purpose of achieving the second object is a non-aqueous electrolyte electric double-layer capacitor, further comprising an organic solvent, wherein a potential window of the phosphazene derivative is within a range having a lower limit of +0.5V or lower and an upper limit of +4.5V or higher, and a potential window of the organic solvent is within a wider range than the potential window of the ph

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