PNNL

Abstract

The effects of carbon microstructure and carbon loading on the performance of Li/air batteries were investigated. The active carbons from various sources were compared, and a dry rolling method was optimized to prepare air electrodes with high mesopore volume. It is found that the capacities of air electrodes improve significantly when the mesopore volume of the carbon source is high. However, for carbons with low mesopore volumes, other factors such as surface activity also play an important role in determining the electrochemical performances of the Li/air batteries. A practical criterion, area-specific capacity, was used to optimize the carbon loading for air electrode. The best area-specific capacity of 13.1 mAh/cm2 was obtained at a carbon loading of 15.1 mg/cm2. Further increasing or decreasing the carbon loading led to a reduced area- specific capacity. Finally, at fixed carbon loading and discharge rates, electrolyte amount was another key factor governing cell performance. A spring mechanism is proposed to explain the formation of the tri-phase regions in air electrodes. After optimizing the parameters listed above, a high capacity of 1,756 mAh/g carbon corresponding to a specific energy of 4,614 Wh/kg carbon was obtained for Li/air batteries operated in a dry air environment.