Nuts and Volts - February 2012

The Edison Cell

By Walter Noon III

With the wild fluctuations in fuel prices over the last few years, world concern over global warming, and simply the idea of creating new and more sustainable technologies, immense interest and progress has developed recently in the world of battery development.

In fact, it seems that every day we hear of a new breakthrough, and another step closer to that long sought elusive goal of a truly workable battery storage system! Perhaps one day soon we’ll have a battery that displays no “memory” effect, one that can be completely discharged or overcharged without harm, and require no complex computerized management system. This battery could even prove so durable it will be immune to damage from vibration and not break down chemically over time. In operation, such a battery might even routinely outlast the very vehicle or machine it was designed to operate in! Last, we could complete our wish list by adding in the impossible: low materials toxicity, simple construction, and, of course, good energy density.

Does such a battery sound like too much to hope for?

Thomas Edison didn’t think so when in 1899 — working with a design pioneered by Waldemar Jungner — he patented a battery with all these characteristics.

It was Edison’s hope that electric vehicles — which currently had the lead in popularity — would easily trump internal combustion or steam to be the vehicle of choice of his time, and ours. The Edison cell had a greater energy density than popular lead acid, and recharged in half the time. Astoundingly, it was not harmed by being fully discharged (even if dead shorted for years), and overcharging occasionally was actually good for the cell. It was even recommended as a monthly exercise in the battery’s manual!

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Edison advertised that the cell had a life of at least four years, but the materials proved to be so stable (due to the low solubility of the reactants in the electrolyte) that some are still producing their full capacity today after more than 50 years! Problems with the Edison cell were few, and included poor performance at low temperatures, a high self discharge rate when unused (20% to 40% per month), and a slower than normal charge and discharge rate (65%). Yet, the practical nature of these cells was undeniable, and perhaps remains so today.

Like many overlooked gems throughout the history of engineering, perhaps these “diamonds in the rough” deserve a second look and some thoughts as to how our present technology could be improved by examining the principles of their operation. Many times historically these cells have been referred to as “the battery that worked too well.” Though they were popular and profitable in niche markets for Edison, it has been said that a business model could never be created for the general public by producing a product that does not require replacement. However, these days where “going green” is more than a quaint idea, perhaps Edison’s idea has finally found its time.