Disproportionation in Li-O2 batteries based on a large surface area carbon cathode

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Kinetics

Background:

• Lithium-oxygen (Li-O2) batteries offer high energy density but face challenges with discharge product stability and reaction mechanisms.
• Understanding the complex discharge process is crucial for optimizing Li-O2 cell performance and cycle life.

Purpose of the Study:

• To investigate the kinetics of the discharge process in Li-O2 cells.
• To elucidate the relationship between discharge kinetics and charge overpotential.
• To characterize the discharge product and its components for improved battery design.

Main Methods:

• Performed a kinetics study on the discharge process of Li-O2 cells with large surface area cathode material.
• Analyzed the charge overpotential in relation to discharge kinetics.
• Utilized scanning electron microscopy (SEM) to observe the morphology and growth of discharge products.

Main Results:

• Identified a first-order disproportionation reaction during discharge, forming two Li2O2 components.
• Characterized an oxygen-rich, superoxide-like component with lower charge potential (3.2-3.5 V) compared to the main Li2O2 component (∼4.2 V).
• Observed discharge products as toroids, assemblies of nanoparticles, with growth and decomposition consistent with the two-component model.

Conclusions:

• The porosity of activated carbon cathodes facilitates the formation of the superoxide-like component.
• The presence of distinct discharge product components influences the charge overpotential.
• Controlling growth conditions to manage discharge product nature is vital for enhancing Li-O2 cell performance.