Nuclear Battery Efficiency Raised

Advanced Battery Technology, Jul 2005

Scientists in the U.S. claim to have increased efficiency on batteries based on nuclear sources tenfold. University of Rochester researchers raised the efficiency by increasing the surface area of the silicon detector.

"For 50 years, people have been investigating converting simple nuclear decay into usable energy, but the yields were always too low," said Philippe Fauchet, professor of electrical and computer engineering at the University of Rochester. "We've found a way to make the interaction much more efficient, and we hope these findings will lead to a new kind of battery that can pump out energy for years."

Betavoltaics uses PN junctions in silicon to convert electrons emitted by tritium gas into a current. Fauchet's technique is to add pits to the silicon surface, so electrons are more likely to strike the junctions. Each pit etched into the silicon is 1 µm wide and 40 µm deep. The PN junction is formed on the inside wall of the pit. By improving the quality of the wells etched into the silicon, the team hopes to achieve much higher efficiencies.

"Our ultimate design has roughly 160 times the surface area of the conventional, flat design," says Fauchet. "We expect to be able to get an efficiency that very nearly matches, and we're doing this using standard semiconductor industry fabrication techniques."

The power source, tritium - H3, has a half-life of 12.3 years, which would directly translate to the battery's lifetime of half its output current.

The gas is relatively safe compared to other nuclear sources as it emits a weak beta particle, transforming to inert helium molecules.

Target applications for the batteries include implanted medical devices, satellites or deep-sea sensors. The technology has been licensed to U.S. firm BetaBatt.