DARPA looking for battery that could power a laptop for months

Drawback: it’s radioactive

Forget recharging or swapping out disposable AAs every day. What if you could power energy-hungry devices for months or even years at a time from a single, reasonably-sized battery? A Washington state-based fusion energy startup is helping to make that dream a reality for DARPA, which wants higher-power radioactive batteries for space. 

Avalanche Energy, which differentiates itself from the rest of the fusion sector by working on portable fusion reactors, announced on Wednesday that it had earned a $5.2 million contract from DARPA through the latter's Rads to Watts program. Begun last year, Rads to Watts' aim is to develop a method for turning "high-power nuclear radiation into kilowatts of electrical energy."

Radioactive batteries already exist, and have for some time, by capturing the decay particles of radioactive isotopes and converting them to electricity. They have the ability to last for decades, centuries, or even millennia, but they produce only a trickle of power for their size compared with conventional batteries. Modern lithium-ion cells, for example, typically store around 200 to 300 watt-hours per kilogram, depending on the chemistry and design. Betavoltaic batteries historically used in niche applications such as implantable medical devices, sensors, and some space systems, on the other hand, usually deliver power in the microwatt- to milliwatt-range.

For those wondering about the radioactive batteries onboard the Perseverance and Curiosity Mars rovers, which generate far more power, they each weigh around 100 pounds, yet are still only able to produce 110 watts, equating to around two and a half watts per kilogram.

According to Avalanche, DARPA wants the radioactive battery it's been commissioned to develop to be able to deliver "more than 10 watts per kilogram" - a major jump in power output for a nuclear battery. According to Avalanche, DARPA is seeking a radioactive battery that could power a laptop-class system for months from a device weighing only a few kilograms. Given DARPA wants its new super-charged radioactive batteries for space and defense purposes, the new battery has to be hardened for space and other extreme environments too. 

Avalanche said it has been commissioned to develop solid-state, micro-fabricated cells able to convert alpha particles into electricity (alphavoltaic), in contrast to the more human-safe beta particles found in things like pacemaker batteries. Alpha particles are easily blocked, but are more harmful to humans. Given the devices powered by this future battery are likely to be in space, that shouldn't be a problem. 

Guess you have to have something to do while the fusion cooks

Avalanche Energy's new endeavor into radioactive batteries isn't that much of a stretch, says the company, as it will involve the creation of technologies that will have direct applications for its mission to develop "practical, portable fusion power." 

"The very same fusion machines that produce high-energy alpha particles will also produce high-energy neutrons," Avalanche explained in a press release. "The neutrons produced are also efficient at creating the same radioisotopes needed for the Rads to Watts program, creating a reinforcing supply-and-technology flywheel around Avalanche's core fusion platform."

As one example of tech produced for Rads to Watts that will support its fusion work, Avalanche pointed to microchips it's developing for the batteries that are used to capture radioactive decay and convert it to electricity. DARPA wants "degradation-resilient" chips for the batteries, and while they'll be capturing alpha particles for now, Avalanche said that they'll be able to use the same chips for their fusion reactor design. 

That fusion reactor design, mind you, is even more far-fetched than 10-watt-per-kilogram nuclear battery technology: It's designed to sit on a desk, apparently. 

Known as the Orbitron, the device is being developed as a 1–100 kWe compact fusion machine, which Avalanche says could suit remote locations, defense uses, transportation, micro-grids, and even lunar surface power thanks to its modular design. The company says demonstrator units of the Orbitron have already been built and tested in-house over the past two years, though it has not reported net-positive energy gain.

In other words, a working version of that miniature, portable fusion reactor is probably 30 years out, too. Good thing they've got that radioactive battery gig to fall back on. ®