Asahi Glass Co., Ltd. has successfully developed a new electric double-layer capacitor with an improved energy density, nearly triple that of the conventional product (Asahi Glass is based in Tokyo and its president is Shinya Ishizu.). The new capacitor has a high capacitance density of 13F/cc per cell volume and the world's highest operating voltage of 3.0V. These features enable the new capacitor to resolve a weakness of capacitors, namely the lack of energy compared with secondary batteries, and provide a high energy density of 10 Wh/liter at a high output range of 1000 W/liter. With this development, we expect that the capacitor will find ready applications in industrial fields, such as in the automotive industry.
In collaboration with ELNA Co., Ltd., an affiliated manufacturer of capacitors, Asahi Glass started development of an electric double-layer capacitor in 1985. The collaboration yielded the successful development of a small, coin-shaped capacitor used primarily for the back-up of IC memories and mass-production commenced at ELNA Co., Ltd. in 1988.
Since that time, we have used the technology developed for the mass production of the coin-shaped capacitor to try to expand the technology for large capacitors in an effort to increase the output power source. We have been independently developing electrode and electrolyte solution to resolve the problem of the shortage of energy density. The features of the electrode and electrolyte that we have recently developed are as follows:
|Electrode: A high-performance molded electrode with high capacitance density and low electric resistance. The main material is special high-purity, high-capacitance, activated carbon, and the electrode is made using the microfibril high-density molding method using fluorocarbon resin PTFE made by Asahi Glass.
|Electrolyte: High-performance organic electrolyte maintaining a high operating voltage and high output, made by combining asymmetrical quaternary ammonium salt, one of our patented technologies, and low polar organic solvent.
To achieve good cost performance, we applied a cylindrical cell structure of a rolled up electrode with good productivity and developed a "Tabless structure" that does not require a lead tab to be pulled out from the electrode, as with the conventional type. The output is increased by improving the volumetric capacitance density through the efficient packing of the devices and by reducing the internal cell resistance. The electric capacitance of a single cylindrical cell is approximately 500 to 2000 F. In addition, we have the technology to set single cylindrical cells as a 14-V/42-V high-voltage module by connecting them in series. In the course of these developments, we have filed approximately 300 patent applications.
The current requirement for automobile application is a high-output from a small-sized power source, so it is expected that there will now be considerable demand for use in hybrid cars and fuel cell cars. The market for hybrid cars in particular is estimated to grow to approximately 2,200,000 units by 2010, so we will be expanding our business by primarily targeting the market for mini-hybrid cars that can maximize the performance of the new capacitor.
|Electric double-layer capacitor
A capacitor that stores electricity in the electric double layer formed at the interface between electrolyte solution containing ions and electrode materials that have a large surface area. With a very large electrostatic capacitance compared with that of a normal capacitor, so it is used as a means of power storage that is capable of charging and discharging. Because of the physical phenomenon of storing charge in the electric double layer, it is possible to discharge a large amount of current and charge the device quickly. There is very low deterioration in performance after repeated charging and discharging, so the power source can be used semi-permanently.
The unit of electrostatic capacitance of a capacitor. When applying a DC voltage of V volts to a capacitor with an electrostatic capacitance of C farads, the electric charge, Q coulombs, stored in the capacitor is expressed as Q = C x V.
|Output density, energy density
When discharging a capacitor at an output of W watts, if the duration of the discharge is represented in hours, the amount of energy E generated at that time is expressed as E = W x h. These values differ according to the size of the capacitor. Therefore, to standardize the performance for comparison, each value is divided by the volume of the capacitor cell in liters and represented as W/liter for output density and Wh/liter for energy density.
|Microfibril high density molding method
When polytetrafluoroethylene (PTFE) is mechanically sheared, it becomes just a few microns thick. The molding method uses this property to immobilize activated carbon powders into the micro fibrillated PTFE network.
|Asymmetrical quaternary ammonium salt
Quaternary ammonium is a positive ion with four alkyl groups attached to each nitrogen atom. Until now, symmetrical quaternary ammonium consisting of the same four alkyl groups has been used. The development of asymmetrical ammonium that unites four different alkyl groups has enabled us to significantly improve the solubility and the electrical conductivity.
|Cylindrical cell structure of rolled up electrodes, series module
This is a cylindrical structure based on a device rolled up with a separator between two long positive and negative electrodes. When it is necessary to drive them at several volts to a high voltage of several hundred volts, multiple single cells are used in a module form, connecting them in series.