Janus Graphene Oxide Sheets with Fe₃O₄ Nanoparticles and Polydopamine as Anodes for Lithium-Ion Batteries

In this study, a one-step process to fabricate "Janus"-structured nanocomposites with iron oxide (Fe₃O₄) nanoparticles (Fe₃O₄ NPs) and polydopamine (PDA) on each side of a graphene oxide (GO) nanosheet using the Langmuir-Schaefer technique has been proposed. The Fe₃O₄ NPs-GO hybrid is used as a high-capacity active material, while PDA is added as a binder due to its unique wet-resistant adhesive property. The transmission electron microscopy image shows a superlattice-like out-of-plane section of the multilayered nanocomposite, which maximizes the density of the composite materials. Grazing-incidence small-angle X-ray scattering results combined with scanning electron microscopy images confirm that the multilayered Janus composite exhibits an in-plane hexagonal array structure of closely packed Fe₃O₄ NPs. This Janus multilayered structure is expected to maximize the amount of active material in a specific volume and reduce volume changes caused by the conversion reaction of Fe₃O₄ NPs. According to the electrochemical results, the Janus multilayer electrode delivers an excellent capacity of ∼903 mAh g^-1 at a current density of 200 mA g^-1 and a reversible capacity of ∼639 mAh g^-1 at 1 A g^-1 up to the 1800th cycle, indicating that this Janus composite can be a promising anode for Li-ion batteries.