Optimization of Air Electrode for Li/Air Batteries

Abstract

The effects of carbon microstructure and loading on the performance of Li/air batteries were investigated. We found that the capacities of Li/air batteries were related to both the specific capacity per unit weight of the carbon source ( mAh g − 1 ) and the carbon locating per unit area ( g cm − 2 ) . Therefore, the product of these two parameters [i.e., the area-specific capacity ( mAh cm − 2 ) ] was introduced to optimize the performance of the air electrode. At the fixed electrolyte amount ( 100 μ L / cell ) , the best area-specific capacity of 13.1 mAh cm − 2 was obtained at a carbon loading of 15.1 mg cm − 2 . Further increase or decrease in the carbon loading led to a reduced area-specific capacity. The capacities of air electrodes increased with increasing mesopore volumes of the carbon sources. The uniformity of the pore sizes also played an important role in determining the electrochemical performances of the Li/air batteries. At fixed carbon loading and discharge rates, the capacity increased significantly with increasing electrolyte amounts. This phenomenon was explained by the formation of extra triphase regions in the air electrodes. After optimizing the electrode and electrolyte parameters, a high capacity of 1756 mAh g − 1 carbon was obtained for Li/air batteries operated in ambient oxygen pressure (0.21 atm).