Influence of the Porous Structure of the Cathode on the Discharge Capacity of Lithium-Air Batteries

In the development of lithium-air batteries, to understand how the porous structure of the cathode affects the performance of the battery system is important because the main electrochemical reaction which occurs in this system is the deposition of Li2O2 in the pores of the cathode. To clarify the relationship between the porous structure of the cathode and the performance of the battery system, we used carbon gels with different pore size distributions as model cathodes and investigated how their pores are filled during discharging by analyzing the structure of cathodes discharged to different depths through N-2 adsorption experiments. The dominant deposit formed during discharging was identified to be Li2O2 by X-ray diffraction. Interestingly, the ratio of the volume of the Li2O2 deposited in fully discharged cathodes to the meso-macropore volume of the cathode was in the range of 0.5-0.6 and was fairly constant among the samples. Such ratios are higher than those of microporous carbon cathodes such as activated carbon cathodes. These results suggest that increasing the meso-macro pore volume of the cathode is effective to obtain large capacities in lithium-air batteries.