In recent years Lithium air (Li-air) battery has attracted considerable attention mainly due to its extreme high specific energy^1,2. The theoretical specific energy is estimated up to 3,000 Wh kg^-1, which is approximately one order of magnitude higher than that of conventional Li-ion battery³. The cathode of Li-air battery is chosen as porous carbon material in most studies, which plays a significant role of Li₂O₂ storage and electron transfer. Good electronic conductivity, fast oxygen diffusion, stable mechanical integrity and sufficient surface area and porosity are required for Li-air battery cathode⁴.

In this study, a simple and scalable method for manufacturing three-dimensional carbon nanotube (CNT) foams as the Li-air battery cathode was being reported. CNT foams were synthesized using poly(methyl methacrylate) (PMMA) microspheres as a template and Polyacrylonitrile (PAN) as a precursor to create crosslinks among CNTs^5,6. The tunable porosity and major pore size afford the opportunity to estimate the influence of cathode pore structure with controlled configuration and properties. A series of CNT foams with high porosity and desired major pore size were tested as cathodes in Li-air cells for single galvanostatic discharge performance. As shown in Fig. 1, the cathode with major pore size of 6 μm achieved a specific capacity over 10,000 mAh g^-1 at a current density of 0.13 mA cm^-2. Meanwhile, a direct inverse correlation between cathode major pore size and cell discharge specific capacity was observed. The electrochemical performance was combined with microscopy, porosimetry and modeling for further discussion. The results revealed that discharge product of Li₂O₂ were mainly deposited in micro-size pores and the reduced pore size favored the discharge reaction due to the increased volume specific surface area.

1. N. Akhtar and W. Akhtar, Int. J. Energy Res., 39, 303–316 (2015).

2. N. Imanishi and O. Yamamoto, Mater. Today, 17, 24–30 (2014).

3. J. P. Zheng, R. Y. Liang, M. Hendrickson, and E. J. Plichta, J. Electrochem. Soc., 155, A432-A437.

4. J. Lu, L. Li, J. Park, Y. Sun, F. Wu and K. Amine, Chem. Rev., 114, 5611–5640 (2014).

5. Y. Cui and M. Zhang, ACS Appl. Mater. Interfaces, 5, 8173–8178 (2013).

6. Y. Cui and M. Zhang, J. Mater. Chem. A, 1, 13984-13988 (2013).