Boasting an energy density similar to that of gasoline, lithium-air (or lithium-oxygen) batteries may one day prove the panacea for the range-anxiety associated with electric vehicles. But first there are a number of challenges that need to be overcome, one of which is the unwanted buildup of lithium peroxide on the electrode which hampers this type of battery's performance. Scientists have now figured out a way that this mess might be avoided – an advance they say could lead to batteries with five times the energy density of those currently available.
By doing away with clunky internal oxidizers and instead drawing on oxygen from the air to power its chemical reaction, lithium-air batteries could feature energy densities with many times that of current lithium-ion batteries.
But an undesirable byproduct of this chemical reaction is the formation of lithium peroxide, which obstructs the electrode's conducting surface. One potential way to overcome this is to alter the electrode and chemical makeup of the electrolyte so that it produces lithium hydroxide instead, as demonstrated by scientists at the University of Cambridge late last year.
But by focusing purely on the electrode, a team at the Argonne National Laboratory has worked out how such a battery could be made to produce lithium superoxide during discharge, rather than lithium peroxide. It says that the lithium superoxide is more easily broken down, dissociating into lithium and oxygen to allow for higher efficiency and an improved life cycle. It could also enable "closed system" lithium-air batteries, which wouldn't require intake of extra oxygen from the environment and would make them safer and more efficient.
"The stabilization of the superoxide phase could lead to developing a new closed battery system based on lithium superoxide, which has the potential of offering truly five times the energy density of lithium ion," says Khalil Amine, a member of the research team.
The formation of the lithium superoxide is attributed to the spacing of iridium nanoparticles in the electrode. While lithium superoxide has traditionally been hard to synthesize due to its thermodynamic instability, the researchers say the iridium atoms look to be a good recipe for its growth moving forward.
"This discovery really opens a pathway for the potential development of a new kind of battery," says Larry Curtiss, a battery scientist at Argonne. "Although a lot more research is needed, the cycle life of the battery is what we were looking for."
The research was published in the journal Nature.
Source: Argonne National Laboratory
