Capacitors II: The Sequel

Supercaps: How material science gave new life to an old technology

In electrical circuitry there have always been three basic ‘passive’ components: resistors, capacitors and inductors. Over time, all of them have improved steadily, in performance, usability, longevity, cost etc. They became smaller, cheaper, more reliable and easier to manufacture. Then, in the second half of the twentieth century, one of them unexpectedly leapt ahead.

The capacitor has had its moment in the sun before. Before batteries had been invented, the only deliberate man-made electrical energy storage device was a capacitor - a Leyden jar: a large glass container with a conductive metal coating on both the inside and outside surfaces. Invented independently around 1745 in the Netherlands and Germany, scientists used them to accumulate static electricity generated by friction. With a lot of effort, a scientist, or a showman, could store say 5 Joules of energy in such a large jar. If discharged quickly you could create a spark but, in reality, the amount of energy was only enough to lift a book from the floor onto a low coffee table.

But after Alessandro Volta introduced the voltaic pile, the first practical battery delivering continuous current in 1800, capacitors retreated backstage. For the next century and a half they became electrical housekeeping. They filtered noise and stabilised circuits. By now rather small, they still maintained the same book-lifting capacity. Every radio, television and computer contained them, but nobody built industries around them. Compared with batteries they seemed very limited.

Then, In 1954 ,Howard Becker, working at General Electric, filed a patent: Low Voltage Electrolytic Capacitor. It concealed more than one surprise.

Becker had found a new way of making capacitors using porous carbon electrodes immersed in an electrolyte. The resulting devices stored vastly, really vastly, more charge than conventional capacitors. His porous carbon contained an astonishing amount of internal area folded into a small volume. Electrical charge spread across all of it. A component that had seemed fundamentally limited suddenly wasn’t. He had invented supercapacitors.

The scale of the improvement is difficult to appreciate. The improvement is many orders of magnitude.

Now capacitors were back in the game vis-à-vis batteries. Battery technology was also improving rapidly though the changes were nowhere near as fast. Batteries still had an advantage on how much energy they could store, but they lost out completely to the new supercapacitors on power, how quickly the energy could be delivered or absorbed. They can charge, and discharge, in seconds, and survive millions of cycles. They are less like fuel tanks and more like fierce springs. Today, whenever electrical storage is considered, and it is considered a lot, supercapacitors are on the menu of possibilities, sometimes as replacements for batteries and sometimes complements to them. The dull passive component has re-emerged, literally, as a powerhouse.

And there are the other surprises of Becker’s patent. In it he writes disarmingly: “It is not known exactly what is taking place in the component...”. And, as so often, his employer, General Electric, didn’t realise what it had and more or less walked away. Other companies, particularly Standard Oil of Ohio in the late 1960s and later NEC in Japan, carried the technology forward into the first commercial supercapacitors.

Howard Becker’s invention continues to change the world and yet the man himself seems sadly lost. He does not have a Wikipedia page or indeed much presence at all on the web. There is no obvious record of when he died or if he even knew what he had achieved.

Becker’s transformative patent points toward something else: the significance of materials science. It is, in some ways, a hidden and fragmented discipline. It’s not taught in schools and sometimes finds it hard to find a unified place even in universities, and yet its critical importance to technological progress is undisputed. Materials scientists point out that “there are no engineering problems, only engineering materials problems” History provides them with plenty of supporting evidence.

The transistor is fundamentally a story about semiconducting materials. Jet engines are largely about high-temperature alloys. Optical fibre is about exceptionally pure glass. Modern batteries are stories about electrode chemistry.

The supercapacitor belongs on the same list.

The capacitor did not become important again because electrical engineers discovered new physics. It became important because materials scientists discovered how to fold something approaching a tennis court’s worth of surface area into a device that fits in the palm of your hand. It makes you wonder how many apparently mature technologies are simply waiting for the right material.

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Becker, H. I. (1957). Low Voltage Electrolytic Capacitor. U.S. Patent 2,800,616.