Your next smartphone or electric vehicle might be powered by a nuclear battery instead of your usual lithium-ion cell thanks to a breakthrough made by University of Missouri researchers. This is bad news for those of you who think that WiFi signals are bad for your health — especially if they’re received by a smartphone situated near your head or gonads — but great news for all of the people who value all-day battery life ahead of increased radiation exposure. The world could probably do with reduced fertility rates anyway, right?
First, just to put your mind at rest: This nuclear battery doesn’t contain a mini nuclear fission reactor — that would be insane (at least given our current grasp of nuclear power generation, anyway). Instead, this battery, developed by Baek Kim and Jae Kwon at the University of Missouri, uses the betavoltaic process to generate electricity. A betavoltaic device, as the name implies, is fairly similar a photovoltaic device — but instead of generating electricity from photons, it generates electricity from beta radiation — i.e. high-energy electrons that are emitted by radioactive elements. A betavoltaic device is constructed in almost exactly the same way as a photovoltaic cell: a piece of silicon (or other semiconductor) is wedged between two electrodes, and when radiation hits the semiconductor it produces a flow of electrons (voltage, electricity).
“But surely having a battery, and thus a mobile device, packed full of radioactive material is a bad idea” I hear you say. And usually, yes, you’d be right. What makes a betavoltaic battery somewhat safe is that beta radiation can be easily stopped with a thin piece of aluminium; gamma radiation, on the other hand, has so much penetrative power that it can only be stopped by a big lump of lead (or other dense metal). This doesn’t mean that beta radiation in itself is safe — it can cause cancer and death — but it’s much easier to control. Just make sure the betavoltaic nuclear battery casing is more than a couple of millimeters thick — and don’t drop it. Ever.
Anyway, back to the University of Missouri’s battery. Basically, Kim and Kwon’s nuclear battery consists of a platinum-coated titanium dioxide electrode, water, and a piece of radioactive strontium-90. Strontium-90 (Sr-90) radioactively decays with a half-life of 28.79 years, producing an electron (beta radiation), an anti-neutrino, and the isotope yttrium-90. Y-90 itself has a half-life of just 64 hours, decaying into more electrons, anti-neutrinos, and zirconium (which is stable). The best thing about using strontium-90 as a fuel is that it produces almost no gamma radiation — so, as far as radioactive materials go, it’s pretty safe and easy to handle. (Still, there’s no avoiding the fact that it’s used extensively in medicine, both for radiotherapy of cancer, and as a radioactive tracer.)
While betavoltaic batteries are fairly old hat — they powered some of the earlier pacemakers, before more advanced chemistries such as lithium-ion arrived — the Missouri researchers say that their addition of water is a key breakthrough. Not only does water absorb a lot of the energy of the beta radiation (in high quantities it’s damaging to the betavoltaic semiconductor), but the beta radiation also splits the water molecules, producing free radicals and electricity.
“Water acts as a buffer and surface plasmons created in the device turned out to be very useful in increasing its efficiency,” Kwon says. “The ionic solution is not easily frozen at very low temperatures and could work in a wide variety of applications, including car batteries and, if packaged properly, perhaps spacecraft.” [Research paper: doi:10.1038/srep05249 - "Plasmon-assisted radiolytic energy conversion in aqueous solutions"]
Ultimately, even if beta radiation can be quite easily contained, I doubt we’ll ever see commercial nuclear batteries. Those headlines about exploding lithium-ion batteries are already scary enough; I can’t imagine Apple or Samsung will ever open themselves up to even worse headlines/lawsuits. (“Smartphone owner dies from acute radiation sickness after dropping his phone”.) There’s also the distinct possibility of terrorists creating a dirty bomb from all of that strontium-90 (which itself isn’t cheap, incidentally).
For now, nuclear batteries will probably only be used in military and space applications, where extreme longevity outweighs any risks. Still, it’s nice to dream of a smartphone or other mobile device that never once needs recharging…