Flexible Free-Standing Fe2O3 Nanoparticle/Carbon Shells/Graphene Films for Advanced Lithium-Ion Batteries

High-capacity anode materials of transition-metal oxides (TMOs) usually undergo low conductivities and drastic volume variation derived from a multielectron-transfer conversion reaction mechanism, which seriously hinder the cycling stability and rate performance toward their commercialization. Herein, a free-standing Fe2O3/C shells/reduced graphene oxide (Fe2O3/C/RGO) film as an additive-free anode is fabricated by a facile twostep strategy accompanied by the physical cross-linking feature of chitosan. In this free-standing structure, the Fe2O3 nanoparticles (NPs) with diameters of 20-30 nm are encapsulated by chitosan pyrolytic C shells and further confined within a highly ordered RGO film. As a consequence, the ultrasmall Fe2O3 NPs can effectively reduce the Li+ diffusion pathway, while the C shell and RGO sheets act as a matrix to alleviate the huge volumetric change of Fe2O3 NPs during the charge/discharge process. Benefiting from the advantages of a free-standing film, the well-designed Fe2O3/ C/RGO film effectively resolves long-standing challenges and achieves an admirable capacity of 609 mAh.g(-1) at 1 A.g(-1), a good rate performance (up to 4 A.g(-1)), and an outstanding cycling performance over 1000 cycles. These results provide a universal strategy to integrate TMOs with RGO to construct a flexible self-supported film for superior lithium-ion batteries.