Oxygen Ion Batteries

A future based on renewable energy is an aspirational goal we’ll never realize without better energy storage technology. Lithium-ion batteries have become the standard for rechargeable cells, but their volatility and low reliability make them a questionable choice for our green future. Researchers from the Vienna University of Technology (TU Wien) have developed an alternative. The team’s oxygen-based battery doesn’t have the same energy density as Li-ion, but it’s much safer and more stable.

Lithium isn’t the only possible fuel for a reversible reduction battery—alternatives like sodium and magnesium have been proposed, too. However, none of the traditional options offer better performance or characteristics than lithium. And using lithium in a future smart grid is a risky proposition. For one, the lithium and cobalt needed for Li-ion batteries are expensive and rare. Lithium-ion batteries also have a habit of overheating and catching fire if they are damaged or stored in high-temperature environments.

According to IEEE Spectrum, the oxygen-ion battery uses the same charge-discharge mechanism as lithium-ion—the oxygen just stands in for lithium. When supplied with voltage, oxygen ions migrate to the oxygen-absorbing electrode to store power. During discharge, the oxygen flows in the other direction to produce a current. The Austrian researchers measured the energy density at 140 milliwatt-hours per cubic centimeter, about 30% of lithium-ion. The tradeoff could be worth it, though.

The study team, led by TU Wein researcher Alexander Schmid, built a small-scale laboratory version of this system (see above), confirming that it still worked after 1,000 charge cycles. However, they believe the oxygen-ion cell could last much longer, potentially into the hundreds of thousands of cycles. Capacity loss in Li-ion cells is often due to ions being diverted by side reactions and parasitic current. The same would happen in oxygen-ion systems, but there’s plenty of oxygen in the air. It should be possible to refresh these batteries with atmospheric oxygen to replace the lost ions.

An oxygen-ion battery also has promise as part of a green energy grid because it would be less delicate than lithium-ion cells. The team says this new battery can operate normally at 200-400 degrees Celsius. The solid electrolyte inside is non-flammable, making it ideal for use in power generating and storage facilities. Even with the lower energy density, oxygen-ion could end up being more affordable—the materials inside, like iron, calcium, and chromium, are all plentiful and stable. Now, someone just has to build a bigger battery.

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