Nanoscale Iron Fluoride Supported by Three-Dimensional Porous Graphene as Long-Life Cathodes for Lithium-Ion Batteries

Abstract

FeF3·0.33H2O wins the favor of researchers for high theoretical capacity and low cost, but practical application is trapped by low intrinsic conductivity and slow Li+ diffusion coefficient. To solve this problem, a three-dimensional (3D) porous graphene-loaded FeF3·0.33H2O nanocomposite is prepared by a non-polluting hydrothermal method and in-situ fluorination. The excellent conductive network of 10–30 nm iron fluoride primary particles and 3D graphene in the composite structure reduces the electrochemical polarization of FeF3·0.33H2O. The 3D porous graphene facilitates the rapid migration of Li+ and reduces the concentration polarization. Therefore, the sample exhibits a high capacity of 205 mAh g−1 at 0.1 C with more than 91% of the theoretical capacity and excellent rate performance of 135.8 mAh g−1 at 6 C. Even cycled over 1400 times at 1.25 C, the specific capacity of 100.2 mAh g−1 is remained, which is only 0.02% attenuation per cycle. Experiments and calculations show that outstanding electrochemical properties of the electrodes are attributed to the improvement of electronic conductivity and ionic conductivity.