Betavoltaic Battery Expected to Live 25 Years

A prototype betavoltaic battery contains layers of silicon carbide and metal foil embedded with the radioactive isotope tritium. When high-energy electrons emitted by the decay of tritium hit the silicon carbide, it produces an electrical current that exits the cell through the metal pins. Image courtesy of Widetronix.)

Semiconductor firm Widetronix is developing a new type of betavoltaic battery that could have a 25-year lifespan. Although the batteries likely will first be used for military applications, they could be used to replace traditional lithium batteries in several biological implants including devices used in neurological stimulators and cardiac-rhythm management, according to the manufacturer. In addition to their long lifespan, the batteries are considered an attractive power source for medical implants because they can withstand harsher conditions than chemical batteries.

The use of betavoltaics in implantable devices is actually not new. The first pacemakers made use of betavoltaics fueled by the radioactive element promethium, but the betavoltaics were phased out after the development of less-expensive lithium-ion batteries. Decades-old semiconductors required a relatively large amount of a radioactive substances to generate a small power output. And, it goes without saying, that some people may be dubious of having radioactively powered devices implanted into their bodies.

Betavoltaic batteries, which harvest energy from the nuclear decay of isotopes, rely on a semiconductor to capture the energy in electrons, or beta particles, produced during the isotopic decay. The lifetime of betavoltaic devices depends on the half-life of the radioisotopes that power them, which can be as great as a century.

The battery prototypes from Widetronix are powered by the decay of the hydrogen isotope tritium into high-energy electrons. Since tritium has a half-life of 12.3 years, the company puts twice as much tritium in its batteries as initially required to make batteries. Hence the 25-year life span. The manufacturer, which is based in Ithaca, NY, USA, is a spin-off from Cornell University’s Wide Bandgap Laboratory.

The batteries are composed of a metal foil impregnated with tritium isotopes and a thin chip of the semiconductor material silicon carbide, which can convert 30% of the beta particles that hit it into an electrical current. “Silicon carbide is very robust, and when we thin it down, it becomes flexible,” says Widetronix CEO Jonathan Greene. “When we stack up chips and foils into a package a centimeter squared and two-tenths of a centimeter high, we have a 1-µW product.” A prototype being tested by Lockheed Martin for military purposes produces 25 nW of power.

For more information on this technology, see “A 25-Year Battery“in Technology Review, published by the Massachusetts Institute of Technology (Cambridge, MA, USA).

For information on another nuclear battery being developed by researchers at the University of Missouri, see our post on medtechinsider titled “Small and Efficient Nuclear Battery Uses Liquid Semiconductor.”

Tags: batteries, betavoltaics, pacemakers, Widetronix