Next Energy News reports the U.S. Air Force Research Laboratory has invented betavoltaic power cells which use radioisotopes as the energy source. Such a battery could potentially power a notebook for years.
The site claims these batteries will be safe and may be available on the market within 2-3 years.
Betavoltaics generate power when an electron strikes a particular interface between two layers of material. The Process uses beta electron emissions that occur when a neutron decays into a proton which causes a forward bias in the semiconductor. This makes the betavoltaic cell a forward bias diode of sorts, similar in some respects to a photovoltaic (solar) cell. Electrons scatter out of their normal orbits in the semiconductor and into the circuit creating a usable electric current.
The profile of the batteries can be quite small and thin, a porous silicon material is used to collect the hydrogen isotope tritium which is generated in the process. The reaction is non-thermal which means laptops and other small devices like mobile phones will run much cooler than with traditional lithium-ion power batteries. The reason the battery lasts so long is that neutron beta-decay into protons is the world's most concentrated source of electricity, truly demonstrating Einstein’s theory E=MC2.
Sounds to good to be true. Well, according to Rupert Goodwins from ZDNet it is. He says the technology isn't really ready yet:
One is that the sort of atomic structures that generate power when bombarded with high energy electrons are the sort that tend to fall apart when bombarded with high energy electrons. While solar cells have the same problem, it's to a much lesser extent. There's a lot of research into making materials that don't suffer so much, but it remains a serious issue.
Secondly, while it's true that a tritium-powered battery will eventually turn into an inert, safe lump of nothing much, and while it's also true that a modest amount of shielding will keep the radioactivity within the battery the while, there's the small problem that if you break the battery during its life the nasties come out.
Thirdly, they don't have a great conversion efficiency. Around 25 percent is the best you can get - which is pretty good, but leaves 75 percent sloshing around as heat. That means a 25 watt battery will get plenty warm.
Lastly, they're not very good batteries. Even the latest devices, which are very clever in the way they saturate a porous structure with the gas and thus usefully capture quite a large number of the energetic electrons, have an energy density of the order of twenty five watts per kilo. Lithium ion batteries, the sort you have in your laptop, manage 1.8 kilowatts per kilo. That's 72 times more bang per gram. Do you fancy carrying a battery 72 times heavier than the one you have at the moment, especially if it's hotter than a sixty watt light bulb?