Flexible binder-free graphene paper cathodes for high-performance Li-O2 batteries

In this study, free-standing porous graphene papers for high-capacity and reversible Li-O2 battery cathodes are investigated. The graphene paper-like films were fabricated by the assembling of graphene nanoplatelets (GNPs) with the aid of graphene oxides (GOs) as a stabilizer, using a vacuum-assisted filtration method. By using GOs as a stabilizer, the GNP/GO films were fabricated with a paper-like form and they exhibited a highly wrinkled and disordered morphology. Moreover, the use of GNPs as a basic material eliminated the need for a post-annealing to recover the intrinsic electrical conductivity of graphene sheets. Subsequently, the GNP/GO paper could be directly used as a Li-O2 battery cathode without any conducting additives and binders. The GNP/GO paper electrode showed a much higher discharge capacity in comparison to the reduced-GO paper and commercially available carbon papers. We also found that toroidal Li2O2 mainly nucleated and grew on discharge, and decomposed on charge with a relatively high O2 evolution/consumption efficiency of 87%. However, a large number of Li2O2 particles grew inside the GNP/GO paper electrode, resulting in severe volume expansion of the electrode. This volume expansion could be the primary reason for the capacity fading on cycling.