Yongqiang Shen

Sheet-like structure FeF3/graphene composite as novel cathode material for Na ion batteries

A sheet-like structure FeF3/graphene composite is successfully synthesized by a novel and facile sol–gel method. The structure and electrochemical performance of the as-synthesized FeF3/graphene composite are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and electrochemical measurement. The results indicate that the FeF3 nanosheets are loaded on the surface of the graphene sheets to form the sheet-like structure hybrid. Fourier transform infrared (FTIR) spectrum confirms that C–F bonds exist in FeF3/graphene composite, and it further indicates that a chemical bond between FeF3 and graphene has been formed and FeF3 can preferably stick to the surface of the graphene. The FeF3/graphene composite as cathode material of rechargeable Na ion batteries (NIB) exhibits a fairly high initial discharge capacity of 550 mA h g−1 at 0.1 C, and it still keeps a capacity of 115 mA h g−1 after 50 cycles at 0.3 C at a range of 1.0–4.0 V for NIB.

Preparation and performance of spherical FeF2.5·0.5H2O nanoparticles wrapped by MWCNTs as cathode material of lithium ion batteries

Spherical FeF2.5·0.5H2O–MWCNTs nanocomposites are synthesized via an ionic liquid (IL) based on precipitation route as a high performance cathode material for lithium ion batteries (LIBs), in which the BMMimBF4 is used as environmentally friendly fluorine source, appropriate solvent and binder. The addition of MWCNTs can not only increase the conductivity of the active material, but also play a role in designing a especial morphology where nano-sized FeF2.5·0.5H2O particles grew up. The structure, morphology and electrochemical performance of the as-prepared samples have been characterized by X-ray diffraction (XRD), Rietveld refinement of XRD pattern, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and charge/discharge tests. The results show that the spherical FeF2.5·0.5H2O–MWCNTs nanocomposites present the cubic crystal structure with the cell volume of 1.13293 nm3. Furthermore, it can deliver a high initial discharge capacity of 324.7 mA h g−1 and stable cycle performance of 175.2 mA h g−1 after 50 cycles at 40 mA g−1 between 1.5 V and 4.5 V. Especially, even at a high current density of 500 mA g−1, the as-prepared material can still display a high discharge capacity of 136.0 mA h g−1.