Batteries and Portable Power

University of Rochester Develops Nuclear Battery

A battery with a lifespan measured in decades is in development at the University of Rochester, as scientists demonstrate a new fabrication method that in its roughest form is already 10 times more efficient than current nuclear batteries —- and has the potential to be nearly 200 times more efficient. The details of the technology are already licensed to BetaBatt Inc. (Houston, TX), which formed to capitalize on the technology, and was recently awarded a technology commercialization grant by the National Science Foundation, which funded the initial research.

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.

Betavoltaics, the method that the new battery uses, has been around for half a century, but its usefulness was limited due to its low energy yields. The new battery technology makes its successful gains by increasing the surface area where the current is produced. Instead of attempting to invent new, more reactive materials, the university team focused on turning the regular material's flat surface into a three-dimensional one. 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.

Holding the batteries back is that so little current is generated -— much less than a conventional solar cell — and as particles in the tritium gas decay, half of them shoot out in a direction that misses the silicon altogether. In order to catch more of the radioactive decay, the researchers decided to use a deeply pitted collecting surface instead of a flat collecting surface 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, the insides are coated with a material to form a p-n junction just one-tenth of a micron thick to induce a current.

The university team is currently working on a technique to create and line the wells in a uniform, lattice formation that should increase the energy produced by as much as 160-fold over current technology.

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