The LiI compound was seen as a possible solution to some of the lithium-air battery’s problems – including an inability to sustain many charging-discharging cycles – but conflicting findings had raised questions about the material’s usefulness for this task.
According to the team, lithium-air batteries would be very lightweight – which would be particularly useful in electric vehicles – but it has been limited in practice because of three issues: the need for high voltages for charging, low efficiency, and low cycle lifetimes, which result from instability in the battery’s oxygen electrode.
Researchers have proposed adding lithium iodide in the electrolyte as a way of addressing these problems. But published results have been contradictory, with some studies finding the LiI does improve the cycling life, while others are said to show that the presence of LiI leads to irreversible reactions and poor battery cycling.
“In this new study,” says MIT postdoc Michal Tulodziecki, “we explored in detail how lithium iodide affects the process, with and without water.”
The team looked at the role of LiI on lithium-air battery discharge. In the presence of both LiI and water, a different lithium compound, LiOH (lithium hydroxide) is said to have been produced, which interferes with the charging process. These observations show that finding ways to suppress these reactions could make compounds such as LiI work better.
This study could also point the way toward selecting a different compound to suppress unwanted chemical reactions at the electrode surface.