Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
1999-02-02
2001-03-06
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C029S025030, C423S44500R
Reexamination Certificate
active
06198621
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarizable electrode and an electric double layer capacitor using the same. More particularly, the present invention relates to an electric double layer capacitor suited to instantaneously supply an electric power, and a polarizable electrode used in the electric double layer capacitor.
2. Description of the Related Art
An electric double layer capacitor is a capacitor having a large capacitance to accumulate charges in an electric double layer. A toxicant material such as a heavy metal and the like is not used as the material of the capacitor. Therefore, a load to environment is small. Also, unlike a secondary battery, a chemical reaction is not brought about. Therefore, the electric double layer capacitor is superior in a cyclic life of a charging and discharging operation. For this reason, the electric double layer capacitor is widely used for a backup power supply of a micro-computer, a memory or the like, instead of the secondary battery.
In recent years, an activated carbon/polyacen composite material as disclosed in Japanese Patent No. 2054380 is invented. Also, an activated carbon layer has become possible to be formed on an aluminum foil by using a binder, as disclosed in Japanese Laid Open Patent Application (JP-A-Showa 57-60828). As a result, an electric double layer capacitor having a large capacitance and a low resistance can be manufactured.
In this way, the electric double layer capacitor starts to be applied to various fields needing power. As such application fields, there are energy regeneration in a hybrid vehicle using an engine along with a motor and an electric vehicle, relaxation of electric power generation variation of solar power generation, wind power generation, a backup power supply for instant power fault, and rush current supply when a motor is started.
In these application fields, it is needed that the electric double layer capacitor has a low resistance and a high voltage so that the power from hundreds of watts to tens of kilowatts can be charged and discharged in several seconds in a high voltage equal to or greater than 100 V.
FIG. 1
is a sectional view illustrating a conventional electric double layer capacitor. Referring to
FIG. 1
, the electric double layer capacitor is composed of a basic cell
6
, terminal plates
7
which are provided on both sides of the basic cell
6
and in which solder is plated on an aluminum foil, sets of bolt and nut, and insulation bushes
8
. The basic cell
6
is composed of collector electrodes
3
, a separator
4
, gaskets
5
and polarizable electrodes
9
. The polarizable electrodes
9
function as positive and negative electrodes. The separator
4
prevents formation of an electric short circuit between the polarizable electrodes
9
and allows ions to pass through the separator
4
. The collector electrodes
3
are electrically connected to an external circuit and do not allow the electrolyte to pass through the collector electrodes
3
. The gaskets
5
are used to insulate the collector electrodes
3
from each other and seals the electrolyte. There may be an electric double layer capacitor having a coin cell structure or a winding structure as electric double layer capacitor using organic electrolyte.
The operation voltage of the electric double layer capacitor is limited to a voltage range in which any electrochemical reaction does not occurs in the polarizable electrode and the collector electrode and further the electrolyte is not resolved. Therefore, the operation voltage is about 1 V in a solution type of electrolyte, and about 2.5 V in an organic type of electrolyte. Usually, it is necessary to connect the basic cells
6
in series based on a desired operation voltage so as to increase a breakdown voltage. Therefore, tens to hundreds electric double layer capacitors must be connected in series in the power application field in which the breakdown voltage equal to or higher than 100 V is required.
Typically, the polarizable electrode
9
of the electric double layer capacitor is composed of activated carbon. The same material is used for both of the polarizable electrodes
9
. The polarizable electrode
9
may be formed as a paste type electrode in which activated carbon powder or activated carbon fiber and electrolyte are mixed. Instead, the polarizable electrode
9
may be formed as a cloth type electrode of activated carbon fibers or resin fiber holding the activated carbon powder. Otherwise, the polarizable electrode
9
may be formed as a solid type electrode in which activated carbon powder and carbon organic are coupled by binder such as Teflon, as disclosed in Japanese Patent Publication (JP-B-Heisei 7-70448). Also, an activated carbon/polyacen composite material are well known as the material of the binder portion for realization of capacitance. As disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 8-97102), the polarizable electrode is also well known in which a part of the polarizable electrode is coated with carbon glass in order to prevent particles from falling off.
As the material of the collector electrode
3
, conductive rubber, conductive elastomer, conductive polymer or the like is used as the solution type electrolyte, and metal such as aluminum or the like is used as the organic type electrolyte.
A porous film made of plastic and non-woven cloth are used as the material of the separator
4
.
Conventionally, the electric connection between the polarizable electrode
9
and the collector electrode
3
is held by pressing with an outer case or bonding with organic binder. For example, a polarizable electrode and a collector electrode are bonded by using conductive adhesive, in Japanese Laid Open Patent Applications (JP-A-Heisei 7-161589, JP-A-Heisei 9-270370, and JP-A-Heisei 8-97102). A polarizable electrode and a collector electrode are formed as a unit by use of organic binder in Japanese Laid Open Patent Application (JP-A-Heisei 8-148388).
An example is disclosed in Japanese Laid Open Patent Application (JPU-A-Heisei 3-73426), in which carbon whiskers are used to couple a polarizable electrode and a collector electrode. Also, an electric double layer capacitor in which an collector electrode is in contact with a sintered polarizable electrode through a conductive metal film is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 3-87010). Further, a technique of pressing an collector electrode and the powder of activated carbon deposited on the collector electrode together with binder by a pressing machine is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 6-196364). In addition, an electrode structure in which fibers of activated carbon are disposed between an collector electrode and an electrode material by electrostatic planting is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-320987).
The resistance of the electric double layer capacitor is composed of the resistance of the polarizable electrode, the resistance of the electrolyte, the contact resistances between the component materials and the resistance of the electrolyte within the polarizable electrode. In order to reduce the resistances of the respective component materials, it is necessary that the resistivity of each component material is reduced, an area thereof is made wider and the thickness thereof is made thinner. The contact resistance can be reduced by increasing a contact area between the component materials. The resistance of the electrolyte within the polarizable electrode is different from the intrinsic resistance of the electrolyte. This is because movement of ions can not follow the change of an applied voltage in a macro pore having a small pore diameter in a sub-micron order.
Such a macro pore contains not only small pores of the activated carbon particle, but also gaps between the activated carbon particles and between the fibers. This resistance can be considered as a diffusion resistance, since the movement of the ions to the electric double layer
Kibi Yukari
Saito Takashi
Dinkins Anthony
Hutchins, Wheeler & Dittmar
NEC Corporation
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