The University of Rochester reports that a newly designed betavoltaic battery (based on the energy from radioactive decay) can run for ten years and is already ten times more powerful than any other previously designed betavoltaic battery:
The technology is geared toward applications where power is needed in inaccessible places or under extreme conditions. Since the battery should be able to run reliably for more than 10 years without recharge or replacement, it would be perfect for medical devices like pacemakers, implanted defibrillators, or other implanted devices that would otherwise require surgery to replace or repair. Likewise, deep-space probes or deep-sea sensors, which are beyond the reach of repair, also would benefit from such technology…
Similar to the way solar panels work by catching photons from the sun and turning them into current, the science of betavoltaics uses silicon to capture electrons emitted from a radioactive gas, such as tritium, to form a current. As the electrons strike a special pair of layers called a “p-n junction,” a current results. What’s held these batteries back is the fact that so little current is generated–much less than a conventional solar cell. Part of the problem is that as particles in the tritium gas decay, half of them shoot out in a direction that misses the silicon altogether. It’s analogous to the sun’s rays pouring down onto the ground, but most of the rays are emitted from the sun in every direction other than at the Earth. Fauchet decided that to catch more of the radioactive decay, it would be best not to use a flat collecting surface of silicon, but one with deep pits.
A layer of silicon riddled with pits, each of which would fill with the radioactive tritium gas, would be like dropping the sun into a deep well lined with solar panels. Almost all of the sun’s rays, no matter which way they were emitted, would strike a well wall. Only those rays that fired straight up and out of the well would be lost. With this reasoning, Fauchet devised a method to excavate pits into a microscopic piece of silicon.
The pits, or wells, are only about a micron wide (about four ten-thousandths of an inch), but are more than 40 microns deep. After the wells are “dug” with an etching technique, their insides are coated with a material to form a p-n junction just a tenth of a micron thick, which is the best thickness to induce a current. The Advanced Materials paper details how these wells were dug in a random fashion, yielding a 10-fold increase in current over the conventional design. The team is already working on a technique to create and line the wells in a much more uniform, lattice formation that should increase the energy produced by as much as 160-fold over current technology.
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