To optimize the performance of aqueous lithium-air battery (LAB), a series of experiments were conducted on the structure and composition of the air-breathing cathode. Using a thin 100μm carbon paper as the backing of cathode yielded good battery discharge performance. However, this thin carbon paper does little to prevent an aqueous catholyte from evaporating. A thin transition carbon nanofiber (CNF) layer bonded with PTFE (Teflon) was introduced into the cathode to alleviate water evaporation, while keeping oxygen diffusion through the cathode. Since oxygen diffusion is a limiting factor when the battery discharges at high current densities, the influence of PTFE content in the transition CNF layer was investigated, together with electrode thickness. An optimal value of 30wt.% PTFE in CNF was found to be the best to balance water evaporation and battery discharge performance. It is shown that a PTFE bonded CNF transition layer can significantly enhance cathode performance for air-breathing aqueous LABs.