Reduction of charge and discharge polarization by cobalt nanoparticles-embedded carbon nanofibers for Li-O2 batteries.

The problem of high charge polarization is one of the most significant challenges in current nonaqueous Li-O2 batteries. The development of an electrode for the oxygen evolution reaction (OER) at reduced overpotential is thus essential. Here, we suggest a binder-free electrode based on Co nanoparticles embedded in carbon nanofibers (Co-CNFs), which simultaneously reduces the charge and discharge polarization and extends cycling stability. Co-CNF gives rise to a lower discharge polarization because of an enhanced oxygen reduction reaction activity compared to Co-free CNF. Although the embedment of Co does not enhance the OER activity, it significantly reduces charge overvoltage by forming easily decomposable amorphous Li2 O2 . A mechanism for the formation of amorphous Li2 O2 is suggested in terms of charge localization induced by the Co NPs. The findings suggest a new electrode design strategy of combining inexpensive metals and carbon materials for modulating the phase of the discharge product.