A prototype of the battery at TU Wien. (Image: tuwien.at)

Li-ion batteries are ubiquitous today, but that does not mean that they are the best solution for all areas of application. A team at TU Wien (Vienna) has developed an oxygen-ion battery that has some important advantages: It does not allow for quite as high energy densities as a Li-ion battery, but its storage capacity does not decrease irrevocably over time: it can be regenerated and thus may enable an extremely long service life. Plus, the oxygen-ion batteries can be produced without rare elements and are made of incombustible materials.

The new battery, which uses ceramic materials, could be an excellent solution for large energy storage systems, e.g., storing electrical energy from renewable sources.

“We have had a lot of experience with ceramic materials that can be used for fuel cells for quite some time,” said TU Wien’s Alexander Schmid. “That gave us the idea of investigating whether such materials might also be suitable for making a battery.”

The ceramic materials studied can absorb and release doubly negatively charged oxygen ions. When a voltage is applied, the oxygen ions migrate from one ceramic material to another, after which they can be made to migrate back again — generating electric current.

“The basic principle is actually very similar to the Li-ion battery,” said Professor Jürgen Fleig. “But our materials have some important advantages.”

One of the main advantages being that ceramics are not flammable — so fire accidents are practically ruled out. Also, there is no need for rare elements.

“In this respect, the use of ceramic materials is a great advantage because they can be adapted very well,” said Tobias Huber. “You can replace certain elements that are difficult to obtain with others relatively easily.”

The battery prototype still uses lanthanum — an element that is not exactly rare but not completely common either. However, even lanthanum is to be replaced by something cheaper, and such research is already underway. Cobalt and nickel — found in many batteries — are not used at all.

Left to right: Professor Jürgen Fleig, Tobias Huber, Alexander Schmid. (Image: tuwien.at)

Arguably the most important advantage of the oxygen-ion battery is its potential longevity.

“In many batteries, you have the problem that at some point the charge carriers can no longer move,” said Schmid. “Then they can no longer be used to generate electricity, the capacity of the battery decreases. After many charging cycles, that can become a serious problem.”

The oxygen-ion battery, however, can be regenerated without any problems; if oxygen is lost due to side reactions, then the loss can simply be compensated for by oxygen from the ambient air.

The new battery is not intended for smartphones or electric cars, because the oxygen-ion battery only achieves about a third of the energy density that one is used to from Li-ion batteries and runs at temperatures between 200 °C - 400 °C. The technology is a boon for storing energy, though.

“If you need a large energy storage unit to temporarily store solar or wind energy, for example, the oxygen-ion battery could be an excellent solution,” said Schmid. “If you construct an entire building full of energy storage modules, the lower energy density and increased operating temperature do not play a decisive role. But the strengths of our battery would be particularly important there: the long service life, the possibility of producing large quantities of these materials without rare elements, and the fact that there is no fire hazard with these batteries.”

Here is a Tech Briefs interview, edited for length and clarity, with Schmid.

Tech Briefs: What were the biggest technical challenges you faced?

Schmid: One of the major technological challenges was, and partly still is, the sealing of the battery. In order to keep its charge, the storage electrodes need to be isolated from the oxygen in the atmosphere; also, oxygen can leak, and this causes a slow self-discharge of the battery. Getting this sealing to be perfectly oxygen-blocking is challenging, and we are still working on improving its oxygen blocking properties.

Tech Briefs: Can you explain in simple terms how the technology works?

Schmid: OIBs work by transferring oxygen — in the form of oxide ions and electrons — between two oxide electrodes. One of those electrodes can take up oxygen easily, while the other more easily releases oxygen. By applying a voltage, oxygen is “pumped” from the oxygen affine electrode to the less oxygen affine electrode — the battery gets charged. Then, oxygen “flowing back” can drive an external electronic load — the battery is discharged.

Tech Briefs: The research paper says, “…But even lanthanum is to be replaced by something cheaper, and research into this is already underway.” How is that research going? Any interesting new findings thus far?

Schmid: This is a topic of ongoing research, so we can’t eliminate lanthanum, but the preliminary results look promising.

Tech Briefs: The paper also says a patent is pending. Potentially, how soon could we see the oxygen-ion battery available?

Schmid: This is really hard to estimate. I expect at least 10 years until the technology is ready for large scale commercial application.

Tech Briefs: Are there any set plans for even further research/testing? What are your next steps?

Schmid: Yes, we will continue to work on this topic, both with a basic research approach and also with a more application focused approach.