Metal working – Barrier layer or semiconductor device making – Barrier layer device making
Reexamination Certificate
2000-05-12
2002-04-30
Nguyen, Ha Tran (Department: 2812)
Metal working
Barrier layer or semiconductor device making
Barrier layer device making
C361S502000, C361S503000, C361S518000, C427S080000
Reexamination Certificate
active
06379402
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for producing an electric double layer capacitor having a low resistance and a large capacitance of at least 10 F.
2. Discussion of the Background
A conventional low resistance large capacitance electric double layer capacitor for power application is such that a pair of strip electrodes each having a thin film polarizable electrode material made mainly of active carbon powder formed on a current collector, are wound with a separator interposed, to form an element, this element is impregnated with an electrolyte and accommodated in a bottomed cylindrical metal container, and an opening of the container is sealed with a sealing member. Further, JP-A-4-154106 discloses an electric double layer capacitor wherein rectangular positive electrode and negative electrode each having a polarizable electrode formed on each side of a current collector, are alternately laminated in plurality with a separator interposed to form an element, the element is accommodated in an angular container, and the element is impregnated with an electrolyte and sealed by a sealing cover. For the electrodes of these electric double layer capacitors, activated carbon having a large specific surface area, is employed.
With conventional electric double layer capacitors employing activated carbon, a usual withstand voltage per unit element is from about 2.0 to 2.8 V in the case of electric double layer capacitors employing a non-aqueous electrolyte, although it may depend also on the selection of the solvent and the solute to be used. The energy is proportional to the square of the voltage. Accordingly, it is desired to increase the output density by increasing the energy density by improvement of the durability against application of a high voltage and by an increase of the capacitance density and by lowering the internal resistance, so that a larger quantity of energy can be taken out rapidly. Further, from the viewpoint of the energy storage, it is desired to improve the voltage-holding property after charging.
JP-A-7-022295 discloses that in a process for producing a coin-shaped electric double layer capacitor employing a non-aqueous electrolyte, a voltage of 2 V is preliminarily applied prior to sealing the container, whereby it is possible to suppress an increase of the thickness of the cell or an increase of the internal resistance with time, even if a voltage of 2 V is applied during charging. However, this electric double layer capacitor has a high internal resistance and a small capacitance, and further the voltage-holding property is also inadequate, and as such, it can not be applied to power application.
Further, JP-A-5-343263 discloses that polarizable electrodes are impregnated with a sulfuric acid electrolyte, a voltage of 1 V is preliminarily applied, then an inert gas is injected, followed by sealing, whereby it is possible to reduce the internal resistance and leakage current and to increase the capacitance. However, this electric double layer capacitor employs an aqueous electrolyte, whereby the useful voltage of a unit element is 1 V at the highest, the energy density is low and the voltage-holding property is inadequate, and therefore it is hardly applicable to power application.
Whereas, in JP-A-10-41199, the present inventors have proposed a method for obtaining a large capacitance electric double layer capacitor which is excellent in the voltage-holding property and which exhibits little decrease with time of the capacitance, by preliminarily applying a voltage slightly higher than the rated voltage.
Heretofore, to increase the capacitance of an electric double layer capacitor, activated carbon having a larger specific surface area has been employed, but there has been a problem that when a high voltage is applied, a gas is likely to be generated by decomposition of the surface functional groups of activated carbon or the solvent of the electrolyte, or by decomposition of impurities contained in a small amount in the capacitor cell. According to the method disclosed in JP-A-10-41199, a gas can be generated prior to the use of the electric double layer capacitor by a preliminary application of a voltage, and this gas can be discharged out of the capacitor container. However, if it is used for a long period of time by applying a voltage continuously for e.g. a few thousands hours, a gas will gradually be generated, to increase the inner pressure of the container, and especially when a readily deformable container such as angular container is employed, there will be a problem that the container tends to swell. Accordingly, it is necessary to take a deformation of the container into consideration, when a module is to be constituted by means of a plurality of capacitors.
Accordingly, it is an object of the present invention to provide a large capacitance electric double layer capacitor having a high withstand voltage, whereby the container is hardly deformable, and the performance is constant even when it is used for a long period of time.
SUMMARY OF THE INVENTION
The present invention provides a process for producing a large capacitance electric double layer capacitor, which comprises a step of forming an element by disposing a positive electrode and a negative electrode containing a carbon material having a specific surface area of at least 500 m
2
/g to face each other with a separator interposed, a step of impregnating the element with a non-aqueous electrolyte and then applying an applied voltage of from 1 to 1.5 times the rated voltage across the positive electrode and the negative electrode, a step of maintaining the element under a reduced pressure, a step of accommodating the element in a metal container, and a step of sealing the metal container.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
this specification, the rated voltage is the maximum working voltage allowable for the guaranteed life as an electric double layer capacitor in a usual working condition. When the rated voltage is not prescribed for a product, a voltage is applied to the electric double layer capacitor at 60° C. for 1000 hours, whereby the maximum voltage at which the volume change can be controlled within 30%, is taken as the rated voltage. Further, in this specification, the element represents one having a positive electrode and a negative electrode facing each other with a separator interposed, which is accommodated in one container for electric double layer capacitor. For example, in a case where a positive electrode and a negative electrode are accommodated in a container as alternately laminated in plurality with a separator interposed, the entire laminate is called an element.
In the process of the present invention, the applied voltage to the element is from 1 to 1.5 times the rated voltage of the electric double layer capacitor. If it is less than 1 time, the effect for improving the voltage holding property is little as compared with a case where no applied voltage is applied, and if it exceeds 1.5 times, the initial capacitance tends to be low, or the internal resistance tends to increase. Preferably, it is from 1 to 1.15 times, particularly preferably from 1.03 to 1.12 times.
The above application of the voltage is preferably carried out at a temperature of from 35 to 85° C. When the voltage is applied while heating, the effect for improving the voltage-holding property increases, whereby the time for applying the voltage can be shortened. If it is lower than 35° C., the heating effect is small, and if it exceeds 85° C., the initial capacitance tends to be low, and the internal resistance tends to increase. Particularly preferred is from 50 to 70° C.
The time for applying the above voltage is preferably at least 2 hours, usually from 5 to 100 hours. If the time for application of the voltage is short, the voltage-holding property can not be increased, and the amount of gas generated during use tends to be large, whereby swelling of the capacitor container tends to increase. On the other hand, if the time for
Hiratsuka Kazuya
Suhara Manabu
Asahi Glass Company Limited
Nguyen Ha Tran
LandOfFree
Method for manufacturing large-capacity electric... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for manufacturing large-capacity electric..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for manufacturing large-capacity electric... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2902013