Bifunctional Composite Catalysts Using Co3O4 Nanofibers Immobilized on Nonoxidized Graphene Nanoflakes for High-Capacity and Long-Cycle Li-O2 Batteries

Designing a highly efficient catalyst is essential to improve the electrochemical performance of Li-O-2 batteries for long-term cycling. Furthermore, these batteries often show significant capacity fading due to the irreversible reaction characteristics of the Li2O2 product. To overcome these limitations, we propose a bifunctional composite catalyst composed of electrospun one-dimensional (ID) Co3O4 nanofibers (NFs) immobilized on both sides of the 2D nonoxidized graphene nanoflakes (GNFs) for an oxygen electrode in Li-O-2 batteries. Highly conductive GNFs with noncovalent functionalization can facilitate a homogeneous dispersion in solution, thereby enabling simple and uniform attachment of ID Co3O4 NFs on GNFs without restacicing. High first discharge capacity of 10 500 mAh/g and superior cyclability for 80 cycles with a limited capacity of 1000 mAh/g were achieved by (i) improved catalytic activity of ID Co3O4 NFs with large surface area, (ii) facile electron transport via interconnected GNFs functionalized by Co3O4 NFs, and (iii) fast O-2 diffusion through the ultrathin GNF layer and porous Co3O4 NF networks.