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Atomic MEMS Battery has 50 Year Charge
notestein writes "Working for DARPA, a couple of Cornell researchers (Amil Lal, Hui Li ) have developed a battery that uses decaying nickel-63 to drive a flexing MEMS cantilever to generate electricity. They expect a production version to produce useful energy for at least 50 years."
Microwave replacement
Heater
Photographic film eraser
Electromagnetical warfare
Rodents killer
Hair remover
And I'm sure Al Qaeda can think of more wonderful uses.
One detail conveniently left out of the article is how much actual *power* is generated by this device. If a 1cc device produces only 10mA sustained, you're far better off with standard batteries for most anything except devices that actually *require* a long-running power source, and don't draw any significant amount of current. Consider this: I use 4 1700mAh AA cells in my digicam. They're, what, 3-4cc each? So at 10mA per MEMS device, you get only 160mA from that same volume.
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The quantity of energy you'd get would be less than the energy of a decaying isotope, which is not very much. Even with advances in technology, this can't be very much.
Actually, this turns out not to be the case.
Consulting Ye Rubber Bible, Nickel-63 liberates about 67 KeV per decay (quite low; decays are typically in the 1 MeV range). This gives an energy density of about 35 kW/hr per _gram_ over the lifetime of the battery. _Energy_ density is far higher than anything based on chemical reactions.
It's _power_ density that's low for most practical battery materials. With a half-life of 92 years, you get about 20 mW per gram released (actually a bit more than that at first; it _averages_ to this as it emits half its decay energy over the whole 92 years).
The nice thing about Nickel-63 is that the decay produces beta rays (high-energy electrons) and nothing else. This could be shielded by a thick sheet of plywood, or a thin sheet of lead. Most radioisotopes aren't nearly as friendly (there is usually gamma emission as the decay product sheds excess energy, which is difficult to shield against). [ObDisclaimer: I'm assuming that the lead also blocks the x-rays produced as the high-energy electrons smack into the shielding.]
The other nice thing is that the decay product is stable and is a solid (Copper), and so both inert and likely to stay in the battery. Carbon-14, the other "friendly" radioisotope that I can think of offhand, has a lower power density (though a higher energy density), and produces a gas as a byproduct (Nitrogen), which could eventually cause problems if allowd to build up near your MEMS devices.