Two commercial carbon blacks, Ketjen black EC600JD (KB600) and Super P with quite different porosity parameters, are used for the cathode of a lithium-air battery. With high specific pore volume, KB600 shows a higher weight specific capacity. However, Super P exhibits a super high volume specific capacity, about 7 times higher than that of KB600, ascribed to its higher proportion of pores with suitable size for the deposition of solid products. The effects of O2 partial pressure and discharge rate on the specific capacity are investigated, combined with characterizations of contact angle and the structure of the electrodes. It is demonstrated that the Super P electrode possesses better O2 transport that improves the use of the whole electrode volume, and the special mechanism of O2 diffusion in the Super P electrode is proposed. By mixing KB600 with Super P with a weight ratio of 5:1, an electrode is obtained that exhibits increased O2 transport. The weight specific capacity is 1219 mAh g−1, about 1.2 times higher than that of KB600.