Hello,

We noticed you're browsing in private or incognito mode.

To continue reading this article, please exit incognito mode or log in.

Not an Insider? Subscribe now for unlimited access to online articles.

Christopher Mims

A View from Christopher Mims

New "Ultra-Battery" as Energy-Dense as High Explosives

Metallized xenon difluoride heralds a new class of solid fuels.

  • July 9, 2010

The energy density of batteries is tremendously important as an enabler of new technologies. Meanwhile, the scramble to create ever more powerful batteries has even led some manufacturers to contemplate powering cell phones with energy-dense hydrocarbons like propane.

This is why the claims made for an extremely early-stage “ultra-battery” recently announced in the journal Nature Chemistry are so remarkable.

“If you think about it, [this] is the most condensed form of energy storage outside of nuclear energy,” said inventor Choong-Shik Yoo of Washington State University. Yoo’s ultra-battery consists of “xenon difluoride (XeF2), a white crystal used to etch silicon conductors,” compressed to an ultra-dense state inside a diamond vice exerting a pressure of more than two million atmospheres.

Applying this level of pressure to XeF2 “metallizes” the substance, pushing all of its atoms closer together, into a new stable state.

This figure shows how the crystal changes color as it changes states, from a relatively soft transparent crystal to a “reddish two-dimensional graphite-like hexagonal layered structure,” and then, above 70 Gigapascals of pressure, to a “black three-dimensional fluorite-like structure,” which is a metal.

In its ultra-dense state, the mechanical energy transmitted to the metallized XeF2 is now stored in the substance itself as a kind of chemical energy. All it takes to release it is a perturbation of a single atom in the crystal, which will cause the entire metallized substance to spontaneously “unzip,” says Yoo.

The reaction would be, quite literally, explosive. In an instant the XeF2 would turn its stored energy into thermal energy with almost 100% efficiency. The XeF2 stores about 1 kilajoule of energy per gram, or “about 10% of the energy stored in a rocket fuel of liquid H2 and O2 mixtures, or about 20% of [the energy stored in] one of the most powerful explosives, HMX,” says Yoo. When viewed as a potential energy storage medium, this discovery qualifies as “a new class of energetic molecules or solid fuels,” he adds.

Until we figure out how to build rocket-powered consumer electronics, the trick to turning XeF2 into a viable means for storing and releasing energy is to figure out what sort of impurities to add to make it “metastable,” just like all the combustible fossil fuels we are surrounded by, which we call plastics.

“If you think about all materials we know, 95% or more are in a metastable state,” says Yoo.

Metastability is a fundamental problem in materials research, and is common to many other substances that metallize and acquire exotic properties after being compressed to an extreme degree, including CO2, N2, O2 etc. If Yoo and his colleagues can conquer this issue for a common substances that can acquire a new molecular configuration at high pressures, they will have created an entirely new means of storing energy.

That goal is a long way off, however - so far Yoo’s discovery has only been synthesized in the lab, in amounts so tiny that when it “unzips” it poses no hazard.

Follow Christopher Mims on Twitter, or contact him via email.

Become an MIT Technology Review Insider for in-depth analysis and unparalleled perspective.

Subscribe today
More from Sustainable Energy

Can we sustainably provide food, water, and energy to a growing population during a climate crisis?

Want more award-winning journalism? Subscribe to Insider Plus.
  • Insider Plus {! insider.prices.plus !}*

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus the digital magazine, extensive archive, ad-free web experience, and discounts to partner offerings and MIT Technology Review events.

    See details+

    Print + Digital Magazine (6 bi-monthly issues)

    Unlimited online access including all articles, multimedia, and more

    The Download newsletter with top tech stories delivered daily to your inbox

    Technology Review PDF magazine archive, including articles, images, and covers dating back to 1899

    10% Discount to MIT Technology Review events and MIT Press

    Ad-free website experience

/3
You've read of three free articles this month. for unlimited online access. You've read of three free articles this month. for unlimited online access. This is your last free article this month. for unlimited online access. You've read all your free articles this month. for unlimited online access. You've read of three free articles this month. for more, or for unlimited online access. for two more free articles, or for unlimited online access.