Lithium Iron Phosphate Cathode Material Modified with a Fluoride-Doped Carbon Layer and Polyaniline Nanoparticles for Lithium-Ion Batteries

LiFePO4 cathode material exhibits suppressed rate performance resulting from its inherently poor electronic conductivity and inferior lithium-ion (Li+) diffusivity. Herein, a dual-coating interfacial engineering strategy has been developed to improve the electrochemical performance of LiFePO4 composites. Initially, a fluoride-doped carbon (FC) layer is constructed on the surface of LiFePO4 through solid-phase sintering. Subsequently, highly conductive polyaniline (PANI) nanoparticles are uniformly coated on the surface of the FC layer through π-π stacking and electrostatic interactions. Experimental investigation and theoretical calculation demonstrate that the dual-coating layer of FC and PANI produces synergistic enhancement effects for the LiFePO4@FC@PANI (LiFePO4@FCP) composites at low rates. First, FC acts as an “induced layer” to induce the conformal growth and facilitate a uniform coating of PANI. Second, FC regulates the local electronic structure and decreases the HOMO–LUMO energy gap. Finally, FC enables a more ordered arrangement of PANI molecular chains and reduces entanglement and steric effects. This synergistic effect establishes a more continuous electron transport channel while lowering interfacial impedance and facilitating Li+ diffusion. The electrochemical performance results indicate that LiFePO4@FCP cathode demonstrates excellent performance (a discharge capacity of 95.8 mAh g–1 at 10 C) and stable cycling (a capacity retention above 70% over 1000 cycles at 5 C). This research proposes a strategy for the development of LFP cathode materials through multilevel interface design.