In a recent paper, He et al. (ChemElectroChem 2014, 1, 2052-2057) described a methodology for measuring out-of-cell oxygen diffusivity in lithium-air battery (LAB) cathodes, combining an electrochemical device with a classical gas-transport model. We will demonstrate here that the authors erroneously assumed that the Knudsen diffusivity of gaseous oxygen in the porous cathode is smaller than the diffusivity in the electrolyte and, consequently, that the oxygen mass transport would limit the current output of the battery. Therefore, it is impossible to determine the oxygen diffusivity in LAB cathodes by using the electrochemical device proposed by the authors, comprising an oxygen pump, the LAB cathode, and an oxygen sensor.