Three‐Dimensional Porous CoFe 2 O 4 /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 CoFe 2 O 4 /graphene composite. The composite is composed of nanoporous CoFe 2 O 4 hollow spheres that are well‐anchored onto nitrogen‐doped graphene sheets (CoFe 2 O 4 @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 CoFe 2 O 4 @3D‐NG electrode delivers an impressively high performance of Na storage, which includes a large initial discharge capacity of 596 mAh g −1 at 50 mA g −1 , a high rate capability of 79 mAh g −1 at 1000 mA g −1 , and a long cyclability of 118 mAh g −1 after 1200 cycles at 500 mA g −1 . This work indicates a promising way to design and fabricate advanced CoFe 2 O 4 ‐based anode materials for high‐performance Na‐storage.