Improving the rate capacity and cycle stability of FeP anodes for lithium-ion batteries via in situ carbon encapsulation and copper doping

Abstract

FeP has emerged as an appealing anode material for lithium-ion batteries (LIBs) thanks to its high theoretical capacity, safe voltage platform and rich resources. Nevertheless, sluggish charge transfer kinetics, inevitable volume expansion and easy agglomeration of active materials limit its practical applications. Here, novel Cu-doped FeP@C was synthesized by a synergistic strategy of metal doping and in situ carbon encapsulation. The optimized Cu-doped FeP@C anode demonstrates a highly reversible specific capacity (920 mAh g−1 at 0.05 A g−1), superb rate performance (345 mAh g−1 at 5 A g−1) and long-term cycle stability (340 mAh g−1 at 2 A g−1 after 600 cycles). The electrochemical mechanism was investigated by cyclic voltammetry, kinetic analysis and DFT calculations. The results reveal that carbon frameworks can improve the conductivity and slow down the volume expansion, with highly dispersed FeP facilitating Li-ion migration during the charge and discharge processes. Additionally, Cu doping leads to rearrangement of the charge density and an additional lattice distortion in FeP, which boosts the electron mobility and enriches the surface-active sites, promoting electrochemical reaction and charge storage. This study presents a feasible and effective design for developing transition metal phosphate (TMP) anodes for high-performance LIBs.