Evaluation and electrochemical analyses of cathodes for lithium-air batteries

The performance of cathodes for lithium-air cells is evaluated from an automotive perspective. Unique aspects of this work include the following. Novel cathode structures are fabricated to improve cell performance operating on air. Convective air flow, critical to automotive operation, is used to evaluate cathode performance, and techniques to mitigate the resulting solvent evaporation from the electrolyte are discussed. The peak power is measured using the standard USABC test procedure, a benchmark for evaluating automotive performance. The importance of the kinetic, ionic, and mass transfer impedances as a function of discharge current density is identified using Tafel slopes, reaction orders, and electrochemical impedance spectroscopy (EIS) data. The distinct processes in the EIS data are identified as the anode-separator interface and the cathode. For the lithium-air cells used in this work, the discharge is controlled by a combination of the ionic transfer impedance at the anode-separator interface and the kinetic and mass transfer impedances in the cathode. Finally, impedance data establish the importance of performing EIS during discharge, not at open circuit voltage, to accurately determine the processes controlling the discharge reaction. The implication of these results to automotive applications for lithium-air batteries is discussed.