Lithium intercalation mechanism into FeF(3)·0.5H(2)O as a highly stable composite cathode material

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 FeF(3)·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 FeF(3)·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 ~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 FeF(3)·0.5H(2)O transitions to an amorphous-like phase through a lithiation process. However, a reversible oxidation change of Fe(3+) ↔ Fe(2+) is identified by the XAS results.