June 18, 2012
An uncommon and highly stable electrolyte endows lithium-air batteries with long operating life and other attractive performance traits, according to a study in Nature Chemistry by researchers in Italy and South Korea (DOI:10.1038/nchem.1376).
Because of the large quantity of energy released in the oxidation of lithium, these devices have the potential to pack a lot more energy into a small, lightweight cell than other batteries—possibly 10 times more than lithium-ion batteries (C&EN, Nov. 22, 2010, page 29).
That high theoretical energy density has made Li-air batteries heavily studied systems for powering electric vehicles over acceptably long driving ranges. Yet several technical challenges, such as short lifetimes, low numbers of charging cycles, and sluggish discharge rates, have prevented these batteries from fulfilling their promise. Researchers believe those problems are connected to lithium oxidation products and intermediates, which include Li2O2 and an anionic oxygen radical, O2·–, a highly reactive species. O2·– decomposes typical electrolytes such as organic carbonate solutions of lithium compounds. Until now, scientists have had little success finding stable alternatives.
Bruno Scrosati and Jusef Hassoun of Sapienza University of Rome, Yang-Kook Sun of Hanyang University, Seoul, and coworkers find that tetraethylene glycol dimethyl ether (TEGDME)-lithium triflate serves as a highly stable Li-air battery electrolyte. On the basis of microscopy and various types of analyses, the group reports that its “preliminary” data provide evidence of reversible formation of Li2O2, fast kinetics, and almost no deterioration in battery performance during more than 100 charging cycles. They propose that the enhanced battery stability may be partly attributed to a fleeting oxygen radical lifetime in the selected electrolyte.
“This contribution is significant in that it demonstrates that Li-air batteries are capable of long cycle life,” says Li-air battery inventor Kuzhikalail M. Abraham, a Northeastern University research professor and battery consultant. Last year, Abraham published a study pointing to the potential of TEGDME-lithium hexafluorophosphate as an electrolyte, but he noted that his test cells exhibited high resistance and charge-capacity loss with continued cycling. The improvement reported now may be related to the design of the carbon-based oxygen diffusion electrode, he says.