Soft-template fabrication of hierarchical nanoparticle iron fluoride as high-capacity cathode materials for Li-ion batteries

Abstract

Iron fluoride cathode material for rechargeable Li-ion batteries has attracted extensive attention in recent years due to its high theoretical energy density (712 mAh g−1, 1951 Wh kg−1) and plentiful sources. However, its poor electronic conductivity, sluggish kinetics and volume effect during cycling cause the fast capacity fading. In this work, a hierarchical nanoparticle iron fluoride has been successfully prepared by reverse micelle soft-template method to improve the sluggish kinetics of ions diffusion and electrons transport in iron fluoride. Hierarchical nanostructure not only promotes the sufficient infiltration and soak of electrolyte, but also provides a path for the rapid diffusion of lithium ions. As cathode material for batteries, the as-prepared hierarchical nanoparticle material delivers a high initial discharge capacity of 526.9 mAh g−1 and a long-term cycle performance with a low capacity fading rate of 0.55% per cycle for 100 cycles at 23.7 mA g−1, which outperforms most FeF3/C materials. Even up to 600 mA g−1, it displays a superior rate performance with discharge capacity of 207.6 mAh g−1. Furthermore, the simple adjustment of the alcohols-water ratio realizes the fabrication of iron fluoride samples with different morphology, microscopic dimension and crystal structure. The results show that the reverse micelle soft template method is a cost-efficient, tunable and potential feasible strategy for the preparation of high-performance iron fluoride material and it can also be extended to the synthesis of other nanoscale metal fluorides.