Three-Dimensional Porous CoFe2O4/Graphene Composite for Highly Stable Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are promising alternatives to lithium-ion batteries (LIBs), because of the low cost and great potential in large-scale energy storage. Herein, we present a simple two-step hydrothermal route to construct a novel CoFe2O4/graphene composite. The composite is composed of nanoporous CoFe2O4 hollow spheres that are well-anchored onto nitrogen-doped graphene sheets (CoFe2O4@3D-NG) with a unique 3D network structure, which can not only offer short pathways for Na+ diffusion and conductive networks for electron transport, but also render sufficient active sites for Na+ interfacial reaction and rigid structural stability for volume expansion. When used as an anode material for SIBs, the CoFe2O4@3D-NG electrode delivers an impressively high performance of Na storage, which includes a large initial discharge capacity of 596 mAhg(-1) at 50 mAg(-1), a high rate capability of 79mAhg(-1) at 1000mAg(-1), and a long cyclability of 118 mAhg(-1) after 1200 cycles at 500 mAg(-1). This work indicates a promising way to design and fabricate advanced CoFe2O4-based anode materials for high-performance Na-storage.