Macroporous Carbon Nanotube (CNT) Foams as Li-Air Battery Cathodes

The cathode microstructure of Li-air battery plays a significant role in Li2O2 storage and electron transfer. Here we report a tunable three-dimensional (3D) hierarchically macroporous carbon nanotube (CNT) foam as an air cathode. Excellent electrochemical performance with a specific capacity over 10,000 mAh g(-1) was achieved, which can be attributed to a combination of sufficiently large tunnels for oxygen transport and an appropriate pore width for oxygen reduction in its pore structure. Also, an inverse correlation between the major pore size of carbon and cell capacity was observed experimentally and a simplified analytical model was proposed to explain this correlation. Based on a combined study of galvanostatic discharge, microscopy, porosimetry and modeling, we found that the discharge product Li2O2 was mainly deposited in micro-scale pores, while the reduced major pore size favored discharge reaction due to increased volume specific surface area.