Enhancing cycling performance of FeF₃ cathode by introducing a lightweight high conductive adsorbable interlayer

Iron fluorides, as a kind of high specific capacity conversion-type cathode materials for lithium rechargeable batteries, are attracting an increasing number of researchers. However, their practical applications are hindered by the poor electrical conductivity and the volume effect during cycling. In this work, a lightweight porous hollow carbon nanofiber (PHCNF) interlayer is proposed to coat on the original FeF₃ cathode to solve these problems. This interlayer is synthesized through a facile carbonizing-activating process using polypyrrole (PPy) as raw material, and plays a difunctional role in trapping the escaped FeF₃ particles and improving the electrical conductivity of electrode. By introducing the high conductive coating layer, an extremely high specific capacity of 217 mAh g⁻¹ for 40 cycles in the 2–4.5 V region is achieved, which is close to the theoretical specific capacity of 237 mAh g⁻¹ for FeF₃. Also, a superior power capability is retained delivering a reversible specific capacity of 193 mAh g⁻¹ at 200 mA g⁻¹ and 101 mAh g⁻¹ even at 1000 mA g⁻¹.