Production and Characterization of Oxygen Electrodes for use in Li-Air Batteries

Abstract

Lithium-Air Batteries (LAB) are one of the most promising upcoming energy storage devices. With a theoretical energy density of 11680 Wh/kg and a practical energy density around 1700Wh/kg a LAB has similar energy densities to gasoline. Furthermore a practical energy density of 1700 Wh/kg would mean a 5-10 fold increase over todays Li-Ion Batteries (LIB) with 100-200 Wh/kg. One of the major limiting factors on performance and round-trip efficiency is the catalyst used. Today´s LAB still suffer from high charge- and discharge overpotentials caused by insufficient catalysts. The major goal is to reduce overpotentials by using bifunctional catalysts catalyzing both the oxygen reduction reaction (ORR) as well as the oxygen evolution reaction (OER). Noble metal catalysts show good performance on both reactions but with increasing prices of noble metals metal oxides have drawn attention recently. In order to optimize the performance of Li-air batteries, it is highly important to understand the kinetics and influence of electrode morphology under different operating conditions. One of the most promising in-situ electrochemical characterization methods is the Electrochemical Impedance Spectroscopy (EIS). After a brief overview of different porous electrode models used in literature for fitting experimental data measured during oxygen reduction on gas diffusion electrodes the porous electrode model of Göhr will be discussed in detail. First results with different multi-layered gas diffusion electrodes (GDEs) using different metal oxides like perovskite type oxides as well as spinel type oxides and various other types of catalysts produced by different production techniques like reactive rolling and mixing, dry powder spraying or vacuum plasma spraying will be shown.