Lithium-air batteries were seen as promising in the 1970s as a potential power source for electric vehicles, offering energy densities that rival gasoline and far exceed conventional lithium-ion batteries. However, over the past few decades, scientists have been unable to overcome challenges in the practical application of this technology, including reversible charging and poor cyclability that lead to battery degradation after a few uses.
A research team from MIT, Harvard University and Cornell University has found a way to isolate and study an enigmatic molecule that may be responsible for the degradation of key components in Li-air batteries – superoxide. of lithium.
“The key to trapping lithium superoxide is to use a containment shell of quinone, a molecule used as an energy carrier in biology,” says Matthew Nava PhD ’17, lead author of a paper on the work, published recently in PNAS. Nava, who is now a postdoctoral fellow at Harvard University working in the lab of Patterson Rockwood energy professor Daniel G. Nocera, contributed to the work as a researcher in the lab of chemistry professor Henry Dreyfus Christopher Cummins, who is a lead author of the study; with Shiyu Zhang of MIT; Katharine Pastore and Kyle Lancaster of Cornell University; and Xiaowen Feng and Daniel Nocera of Harvard.
Like many discoveries, this one started as an accident. While a graduate student in the Cummins group, Nava noticed that lithium peroxide turned blue when it approached quinone, representing a rare color change of two reactive solids. Although they knew that the lithium superoxide intermediate must be present in this new material, this was difficult to prove, since the intermediate was buried in a highly colored, detonation-prone quinone shell.
Lithium-air batteries operate by transferring electrons from a large surface area cathode to oxygen gas during discharge, generating deposits of lithium peroxide, the crucial storage material for this class of batteries. Lithium superoxide, formed during charging and discharging, is too unstable and short-lived at room temperature for scientists to study reliably; thus, being able to generate and stabilize this crucial intermediate is an important step towards the development of a viable lithium-air battery.
“The limited cycling [of li-air batteries] indicate that our understanding of the metal oxides that form the energy storage unit of these batteries is incomplete,” explains Nava. “This work demonstrates how encapsulation or physical confinement with specific materials could be a powerful method to prevent electrolyte and cell degradation in these batteries and increase cell cyclability.”
As the world slowly transitions to renewable energy sources, the intermittency issues and challenges of converting renewables into usable fuels must be addressed. Batteries may play a crucial role in the need for reliable and efficient energy storage, and this discovery may have provided a vital key to pave the way forward.