The preparation and characterization of iron fluorides polymorphs FeF3•0.33H2O and β-FeF3•3H2O as cathode materials for lithium-ion batteries

Two kinds of iron fluorides, FeF3 center dot 0.33H(2)O and beta-FeF3 center dot 3H(2)O,.have been synthesized by different chemical routes using Fe(NO3)(3)center dot 9H(2)O and NH4F as precursors and investigated as cathode materials for secondary lithium batteries. beta-FeF3 center dot 3H(2)O was obtained via a mechano-chemical process and FeF3 center dot 0.33H(2)O was obtained by a precipitation reaction from ethanol solution. To further improve their electrochemical properties, a ball milling process with carbon has been used to form composites. The fluorides were characterized by X-ray diffraction (XRD), thermal analysis, FTIR spectroscopy, galvanostatic charge/discharge and cyclic voltammetry measurements. The results showed that the as-prepared B-FeF3 center dot 3H(2)O/C exhibited better rate performance and cycling stability. It exhibited an initial discharge capacity of 199.6mA h g(-1) at a current density of 20 mA g(-1) in a voltage range of 1.8-4.5V and still reserved a discharge capacity of about 146.5 mAhg(-1) after 10 cycles. Only a capacity loss of 15 mAhg(-1) and 7 mA hg(-1) was observed when the current density was at 40 mAg(-1) and 80 mAg(-1), respectively. (C) 2014 Elsevier Ltd. All rights reserved.