The problem of high charge polarization is one of the most significant challenges in current nonaque-ous lithium-oxygen ($Li-O_2$) batteries. The development of oxygen electrode which reduces oxygen evolution reaction (OER) overpotential is thus essential to remedy this problem. Here, we suggest a binder-free electrode based on Co nanoparticles-embedded carbon nanofibers (Co-CNFs), which simultaneously reduces the charge and discharge polarization and greatly extends cycling stability more than six fold. The Co-CNF low-ers discharge polarization because of an enhanced oxygen reduction reaction (ORR) activity compared to the Co-free CNF. Even though the embedment of Co does not enhance OER catalytic activity, it significantly reduces charge overvoltage by forming easily decomposable discharge product, amorphous $Li_2O_2$. A mecha-nism for the amorphous $Li_2O_2$ formation was suggested in terms of charge delocalization induced by the Co NPs. The findings suggest a novel electrode design strategy of combining inexpensive metal nanoparticles and carbons for modulating the phase structure of discharge products.