Li-O2 Kinetic Overpotentials: Tafel Plots from Experiment and First-Principles Theory

Area of Science:

• Electrochemistry
• Materials Science

Background:

• Lithium-oxygen (Li-O2) batteries offer high theoretical energy density.
• Understanding kinetic overpotentials is crucial for optimizing cycle efficiency.
• Current research focuses on identifying key limitations in Li-O2 battery performance.

Purpose of the Study:

• To investigate the current dependence of kinetic overpotentials in Li-O2 batteries.
• To compare experimental Tafel plots with theoretical predictions.
• To determine the primary factors limiting high-current operation in Li-O2 batteries.

Main Methods:

• Experimental measurement of Tafel plots in a bulk electrolysis cell.
• First-principles theoretical calculations for comparison.
• Analysis of kinetic overpotentials and cell impedance.

Main Results:

• Kinetic overpotentials for Li-O2 discharge and charge are found to be small at practical current densities.
• Experimental Tafel plots show semiquantitative agreement with theoretical results.
• Kinetic overpotentials are significantly smaller than iR drop losses due to cell impedance.

Conclusions:

• Minimizing cell impedance is more critical than minimizing kinetic overpotentials for developing high-current Li-O2 batteries.
• Achieving ~85% cycle efficiency at 10 mA/cm² is theoretically possible if only kinetic limitations were present.
• Focusing on reducing cell impedance could unlock higher performance in next-generation Li-O2 batteries.