Vapor-Phase Oxidative Polymerization Enabled Carbon-Coated FeF2 Cathodes With Enhanced Electrochemical Performance

Abstract

FeF₂ is a promising cathode material for high-energy lithium-ion batteries owing to its high theoretical specific capacity, low cost, and environmental benignity. However, its practical application is severely hindered by low intrinsic electronic conductivity and sluggish reaction kinetics, resulting in poor cycling stability and limited rate performance. Carbon coating is widely regarded as an effective strategy to improve its electrochemical performance. Herein, a vapor-phase oxidative polymerization strategy followed by a low-temperature carbonization process is proposed to construct a polypyrrole-derived carbon coating on FeF₂ particles (FeF₂@coPPy). The effects of carbonization time (1, 4, 8 h) on the composition, morphology, and electrochemical properties of the materials were systematically investigated. Prolonged carbonization enhances the carbonization degree of polypyrrole, resulting in improved electronic conductivity and electrochemical performance. However, excessive carbonization induces partial oxidation of FeF₂ to Fe₂O₃ and particle agglomeration, which deteriorate electrochemical properties. Benefiting from an optimized carbon shell and preserved phase integrity, FeF₂@coPPy-4 delivers the best overall performance, maintaining a reversible capacity of 207.2 mAh/g after 100 cycles at 0.1 C and exhibiting excellent rate capability. This work demonstrates a versatile and effective vapor-phase coating strategy for advancing metal fluoride cathodes toward high-performance energy storage applications.