3-D binder-free graphene foam as a cathode for high capacity Li–O2 batteries

Abstract

To provide energy densities higher than those of conventional Li-ion batteries, a Li–O₂ battery requires a cathode with high surface area to host large amounts of discharge product Li₂O₂. Therefore, reversible formation of discharge products needs to be investigated in Li–O₂ cells containing high surface area cathodes. In this study, a binder-free oxygen electrode consisting of a 3-D graphene structure on aluminum foam, with a high defect level (I_D/I_G = 1.38), was directly used as the oxygen electrode in Li–O₂ batteries, delivering a high capacity of about 9 × 10⁴ mA h g⁻¹ (based on the weight of graphene) at the first full discharge using a current density of 100 mA g_graphene⁻¹. This performance is attributed to the 3-D porous structure of graphene foam providing both an abundance of available space for the deposition of discharge products and a high density of reactive sites for Li–O₂ reactions. Furthermore, the formation of discharge products with different morphologies and their decomposition upon charge were observed by SEM. Some nanoscaled LiOH particles embedded in the toroidal Li₂O₂ were detected by XRD and visualized by TEM. The amount of Li₂O₂ formed at the end of discharge was revealed by a titration method combined with UV-Vis spectroscopy analysis.