Graphene is considered as a promising cathode candidate for Li-O2 batteries because of its excellent electronic conductivity and oxygen adsorption capacity. However, for Li-O2 batteries, the self-stacking effect caused by two-dimensional (2D) structural properties of graphene is not conducive to the rapid oxygen transport and mass transfer process, thereby affecting the electrode kinetics. Here, we successfully prepared three-dimensional (3D) graphene with different scales by plasma-enhanced chemical vapor deposition and physical pulverization strategies, in which CH4 is the carbon source and H2/Ar mixed gas is the etching gas. Meanwhile, we fabricated 3D graphene-based Pt nanocatalysts by an ultraviolet-assisted construction strategy and then applied them in Li-O2 batteries. Systematic studies reveal a special relevance between electrochemical performance and graphene particle size, and the smaller-sized 3D graphene can better maintain the microstructure distribution in both the Pt embedding process and electrochemical applications, which is beneficial to the transport of oxygen and Li ions, lowering the decomposition energy barrier of Li2O2, and further obtaining reduced charge overpotential (0.22 V) and prolonged cycle life for Li-O2 batteries. Finally, we anticipate that this work could promote the practical application of 2D materials and larger-sized 3D materials in Li-O2 batteries.
Keywords: Li−O2 batteries; PECVD; Pt nanocatalysts; charge overpotential; three-dimensional graphene; ultraviolet-assisted.