Oxygen reduction by lithiated graphene and graphene-based materials.

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Lithium-air batteries (LABs) offer high theoretical energy density, surpassing lithium-ion batteries.
• Carbon materials are favored as LAB cathodes due to their properties, but poor cyclability hinders practical application.
• The reactivity of carbon cathodes with oxygen reduction products remains unclear, limiting battery performance.

Purpose of the Study:

• To investigate the reactivity of graphene and graphene-based materials with oxygen reduction products in lithium-air batteries.
• To elucidate the mechanisms behind the poor cyclability of carbon cathodes in LABs.
• To identify stable and reactive species for improved LAB cathode design.

Main Methods:

• In situ X-ray photoelectron spectroscopy (XPS) was employed to directly study the reactions.
• Graphene and graphene-based materials were tested for reactivity.
• Lithium peroxide (Li2O2), lithium oxide (Li2O), and in situ generated potassium superoxide (KO2) were used as model reactants.

Main Results:

• Graphene and graphene-based materials showed no reaction with Li2O2 and Li2O, even at elevated temperatures.
• Potassium superoxide (KO2) demonstrated strong reactivity with graphene.
• These findings contrast with the thermodynamic favorability of Li2O2 and Li2O reactions with carbon.

Conclusions:

• The poor cyclability of carbon cathodes in LABs is not due to reactions with Li2O2 or Li2O.
• Superoxide species are highly reactive with graphene, suggesting they play a critical role in cathode degradation.
• Understanding these reactions is crucial for designing stable and efficient LAB cathodes.