Web Japan > NIPPONIA No.28 > Special Feature*
NIPPONIA No.28 March 15, 2004

Special Feature*
New Capacitors To Change Energy Lifestyles
The Nanogate Capacitor is attracting plenty of attention as a dramatic innovation in electric energy storage. What are capacitors, and how can they help solve energy and environmental problems? Will they change the way we live? Find out the answers in this report from the center of today's capacitor development.
Written by Takahashi Koki, Photos by Sakai Nobuhiko
Other photo and illustration credits: Okamura Laboratory, Inc.; Honda Motor Co., Ltd.

Okamura Michio is leading the way in capacitor research.
A green, eco-conscious world would have emission-free electric cars and be powered by solar panels and wind turbines using natural energy sources. But this ideal is still far off, partly because of limitations in today's batteries. An electric car today carries a 400-kg lead battery that must be charged often, and replaced one day. Solar panels function only when the sun shines, and wind turbines turn only when the wind blows, so a backup electrical supply is needed. These energy systems are limited because there is still no efficient, economical way to store electric energy.
But the world of electric storage devices is being radically altered by a new technology, Energy Capacitor Systems® (ECaSS).
Capacitors store electric energy as electricity, so in theory they are an efficient storage medium, more efficient than lead-acid batteries that must first convert electric energy into chemical energy in order to store it, or hydroelectric stations that pump water to a higher level, storing it there to generate electricity later.
Capacitors have a history going back more than 250 years to the invention of the Leyden jar, a device that stores static electricity. Today, capacitors are used as condensers, one of the components required in electronic devices everywhere.
But as storage devices, conventional capacitors have a drawback—their energy density (the amount of electric energy they can store per unit weight or volume) is small, so they cannot store much energy unless they are very large and very heavy. Theoretically speaking, if we were to replace an electric car's 400-kg lead-acid battery with a conventional capacitor storing the same amount of electric energy, the capacitor would have to weigh about 20 times more than the battery—8 tons!
This problem was solved by a researcher named Okamura Michio.
On New Year's Day, 1992, Okamura was playing with a neighbor's cat in his garden. The cat had thick, fluffy hair. Okamura happened to have a thin plastic writing pad, and he began rubbing the cat's hair with it. This created static electricity, making the cat's hair stand on end and causing a crackling sound.
Okamura says, "At that moment, it hit me—it is more efficient to store electric energy as electricity, and it should be possible to store plenty of that energy using ultra-thin electric double layers. All of the concepts I needed to develop ECaSS came to me at that moment."
An electric double layer is formed at the interface between an electrode and an electrolyte. One layer forms at the positive electrode, the other at the negative electrode. This phenomenon was discovered by the German physicist Helmhortz more than 120 years ago.
The electric double layer acts like an insulating membrane until the voltage exceeds a certain limit, after which electrolysis begins. The "membrane" has the thickness of only one layer of electrolyte molecules. It is so thin that its thickness cannot even be compared to the thickness of conventional films that are used as insulating membranes. ECaSS, designed according to this principle, has a much larger energy density than conventional capacitors, making Okamura's capacitors significantly smaller.


   Special Feature*    Wonders of Japan    Living In Japan
   Why Not Try Growing a Bonsai Tree?    Japanese Animals and Culture
   Bon Appetit!    Japan Travelogue    Cover Interview    In Japan Today