Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
2001-04-23
2003-10-07
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S303000
Reexamination Certificate
active
06631073
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrode material for a battery and electric double layer capacitor, a method of producing the same, a battery, and an electric double layer capacitor, particularly to an electrode material which is most suitable for forming an electric double layer capacitor having a large capacitance and large current discharge capability, and a method of producing the same.
BACKGROUND ART
As materials having the capacity to adsorb various substances or ions, for example, powdered activated carbon, granular activated carbon and fibrous activated carbon have been known and are widely used as electrode materials for various batteries, various adsorbents used in water purifiers, deodorization apparatuses, decoloration apparatuses or the like and catalyst carrier. These activated carbons are prepared by activating a carbon material mainly made from coconut shell, coal, lumber or bamboo as a raw material in the presence of steam or in the presence of zinc chloride or potassium hydroxide, and include numerous fine pores therein.
These fine pores are generally referred to as submicropores when the pore diameter is smaller than 0.7 nm, micropores when the pore diameter is within a range from 0.7 to 2.0 nm, mesopores when the pore diameter is within a range from 2.0 to 50 nm, and macropores when the pore diameter is 50 nm or larger.
According to a conventional method of preparing the activated carbon, although activated carbon including micropores having a pore diameter within a range from 0.7 to 2.0 nm and submicropores having a pore diameter smaller than 0.7 nm developed therein are made, formation of mesopores having a diameter within a range from 2.0 to 50 nm is insufficient and the volume of mesopores account for less than 10% of the total volume of pores. Such an activated carbon has a large specific surface area and excellent capability to adsorb molecules having a size smaller than 2.0 nm, but is not capable of efficiently adsorbing and desorbing an organic compound and an inorganic compound, which are used as an electrolyte of the electric double layer capacitor, and aggregates of larger size whichare formed through solvation of these substances.
In view of the adsorption and desorption properties appropriate for the molecule size of the adsorbed material, it is desirable to prepare an activated carbon that has pores of only a specific size. However, no adsorbent having a pore size distribution that is specific in a particular range of pore sizes has been obtained in the mesoscopic pore range.
Although such an activated carbon that supports transition metals or transition metal compounds and has a catalytic action to decompose a material adsorbed onto the activated carbon and electrode materials having a large capacitance have been reported no activated carbon-supported transition metal having a pore size distribution that is specific in a particular range of pore sizes has been obtained in the mesoscopic pore range, as described above. Also, because the activated carbon is processed to support the transit ion metal's or transition metal compounds by adsorption of the transition metals or transition metal compounds after the activated carbon has been prepared, in case the activated carbon is immersed in an electrolytic solution for use as an electrode material, for example, there is such a problem that the supported metal elutes. Therefore, an electrode material that has satisfactory electrical characteristics and stable charge and discharge characteristics has not been made available.
In recent years, demands for an electric double layer capacitor that utilizes activated carbon as the electrode material have been increasing as the backup power source, auxiliary power source and other uses, and are attracting much attention with the development of the electronics industry.
More recently, it has been called for to reduce the size of memory backup power sources further, and develop a secondary battery that can be used as an auxiliary power source having a large capacity and capability to supply a large current instantaneously such as the onboard power source for vehicles.
Activated carbon has a large specific surface area and high chemical stability, and therefore, electrode materials that consist mainly of activated carbon are used as both positive and negative electrodes, for the polarizing electrodes of an electric double layer capacitor.
While the capacitance of the electric double layer capacitor is dependent on the specific surface area, packing density and internal resistance of the electrode material and other factors, particularly important is the relationship between the size of the electrolyte ions included in the electrolytic solution that forms the electric double layer and the size of the pores formed in the electrode material.
In those that are referred to as the electric double layer capacitors of an organic solvent base that utilize an ammonium ion, phosphonium ion or the like, among the electric double layer capacitors, it is said that pores having a pore diameter of 2 nm or larger in the electrode material contribute to the capacitance. Also, in a water-based electric double layer capacitor that uses sulfuric acid as the electrolyte, it is believed that pores having a pore diameter of 2 nm or larger contribute to the performance such as capacitance and current density. Thus, it is expected that excellent materials for electrodes of an electric double layer capacitor or battery will be made from an activated carbon that includes pores having a pore diameter within a range of X±&agr; nm (3.0≦X<10, &agr;=1.0; range of pore size distribution) of which volume accounts for 15% or more of the total volume of mesopores having a pore diameter within a range from 2.0 to 50 nm.
When using a metal supporting activated carbon made by dispersing a large amount of a transition metal or a transition metal compound in an activated carbon as the electrode material, electrolyte that has migrated into the electric double layer is taken into the transition metal or transition metal compound that is present in the activated carbon, and therefore, a greater amount of energy can be stored in comparison to a case in which the electric double layer is used individually. Thus, an activated carbon that includes pores having a pore diameter within a range of X±&agr; nm (3.0≦X<10, &agr;=1.0; range of pore size distribution) of which volume accounts for 15% or more of the total volume of mesopores having a pore diameter within a range from 2.0 to 50 nm, and contains 0.01 to 50% by weight of a transition metal or a transition metal compound will make excellent electrodes for an electric double layer capacitor or a battery.
The thickness of the electric double layer formed from ions that are adsorbed onto the inner surface of pores in an electrode material is believed to be about 1 nm. Since the pore diameter must be 2 nm or larger in order to form the electric double layer evenly on the inner surface of the pores, a conventional activated carbon of which pores consist mainly of micropores having a pore diameter of 2 nm or less is not suited for use as an electrode material for large capacitance and large current discharge. Moreover, in a conventional activated carbon of which pores consist mainly of micropores having a pore diameter of 2 nm or less, the speed of migration,of the electrolyte ions generated through salvation becomes slower which is believed to make such an activated carbon unsuited for use as an electrode material for large capacitance and large current discharge.
Accordingly, an activated carbon, which is made by supporting a transition metal or transition metal compound on the conventional activated carbon of which pores consist mainly of micropores having a pore diameter of 2 nm or less, does not have such pores for the electric double layer to be formed evenly over the inner surface thereof, and the speed of the electrolyte ions to migrate in the pores becomes slower, and therefore, the act
Ibaraki Satoshi
Kojima Kenji
Marumo Chisato
Muto Akinori
Sakata Yusaku
Dinkins Anthony
Flynn ,Thiel, Boutell & Tanis, P.C.
Kanebo Limited
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