Lithium intercalation mechanism into FeF3 center dot 0.5H(2)O as a highly stable composite cathode material

Abstract

The growing demand for lithium-ion batteries (LIBs) requires investigation of high-performance electrode materials with the advantages of being environmentally friendly and cost-effective. In this study, a nanocomposite of open-pyrochlore-structured FeF3 center dot 0.5H(2)O and reduced graphene oxide (RGO) is synthesized for use as a high-performance cathode in LIBs, where RGO provides high electrical conductivity to the composite material. The morphology of the composite shows that FeF3 center dot 0.5H(2)O spheres are embedded into RGO layers and high-resolution TEM image shows that those spheres are composed of primary nanoparticles with a size of similar to 5 nm. The cycling performance indicates that the composite electrode delivers an initial high discharge capacity of 223 mAh g(-1) at 0.05 C, a rate capability up to a high C-rate of 10 C (47 mAh g(-1)) and stable cycle performance at 0.05 C (145 mAh g(-1) after 100 cycles) and 0.2 C (93 mAh g(-1) after 100 cycles) while maintaining high electrochemical reversibility. Furthermore, the responsible electrochemical reaction is investigated using in-situ XRD and synchrotron-based X-ray absorption spectroscopy (XAS), and the XRD results show that FeF3 center dot 0.5H(2)O transitions to an amorphous-like phase through a lithiation process. However, a reversible oxidation change of Fe3+<-> Fe2+ is identified by the XAS results.