Lithium-air batteries have the potential to be the next big leap in battery tech because they get rid of a lot of the weight and complexity involved with standard batteries. That's because, instead of having all the battery components stored inside the battery itself, lithium-air batteries use oxygen in the atmosphere to bring some electrons to the party. There has been some progress in terms of getting air into the battery and having the oxygen react once it gets there, but the technology still faces a significant challenge: reactive oxygen tends to also react with the battery's components.

The result of these reactions is that existing lithium-air batteries can typically only handle a handful of charge/discharge cycles before they start to decay. But researchers have now found an electrolyte material that doesn't react with oxygen, allowing stable performance over multiple charging cycles. And the theoretical capacity of the battery was staggering, possibly more than ten times that of the lithium-ion tech on the market.

The problem has been, as the researchers put it, that lithium-air batteries have an end-point of lithium peroxide (Li 2 O 2 ), which forms through an intermediate oxygen radical. That radical is very reactive and will generally decompose the electrolyte that shuttles charged ions around between the battery's two electrodes. If it's not possible to avoid the reactive oxygen, the authors reasoned, the best thing to do is to change the electrolyte to something that doesn't react with oxygen.

Some preliminary research in this area had been done, but the initial materials would only conduct charges well at temperatures above 70°C. The authors came up with a mixture of an ethylene glycol derivative (tetra(ethylene) glycol dimethyl ether) and a complex lithium salt, LiCF 3 SO 3 . This worked well at room temperature and, perhaps most significantly, the authors found it went through oxygen reactions so quickly that they couldn't detect any reactive oxygen intermediates. "Equally importantly, the peak corresponding to LiCO 3 +—one of the most likely products of electrolyte decomposition—is not seen," the authors note.

This chemical stability also translated to stable performance, with the behavior on the 20th charge/discharge cycle being difficult to distinguish from the 100th. It also performed well across a variety of charges, from half an amp/gram of electrode material up to 3A/g.

The difficulty of interpreting these results is that the electrode is only one part of a larger assemblage. Although the authors take some pains to argue that the electrode they measure is a major component of the battery's weight, it's still difficult to compare to other battery technology.

That said, the authors calculate a theoretical capacity that's nothing short of jaw-dropping. At a high discharge rate, they figure it can handle up to 13,500Wh/kg of electrode. "Even assuming a reduction factor of one order of magnitude due to the weight of the ancillary components, such the cell case, current collectors and electrolyte, the practical energy density may be estimated at a value much higher than that offered by the present lithium-ion battery technology," they argue.

For comparison, current lithium technology is at around 150Wh/kg, and the most promising hardware that has been announced might be able to double that. If the authors' order-of-magnitude estimate is right, it would still place this battery at 10 times the capacity of the current generation of lithium-ion batteries.

Nature Chemistry, 2012. DOI: 10.1038/NCHEM.1376 (About DOIs).

Listing image by Raymond Yee