Iron-Based Fluoride Conversion Cathodes: Mechanisms, Design Strategies, and Challenges for High-Energy Lithium-Ion Batteries

Abstract

Iron-based fluorides (FeF₃, FeF₂) are used as conversion-type cathode materials. With their high theoretical specific capacity, abundant resources, and low cost, they have become promising candidates for next-generation high-energy-density lithium-ion batteries. However, their inherent low electronic and ionic conductivity, significant volume changes, complex phase transition processes, and unstable electrode/electrolyte interfaces severely limit their electrochemical performance and practical applications. This paper provides a systematic review of performance regulation and functionalization design strategies for iron-based fluoride cathode materials in recent years. First, we conduct an in-depth analysis of the distinct lithium storage mechanisms in FeF₃ and FeF₂, highlighting the resulting performance differences and challenges. Furthermore, we highlight recent research advances in improving charge transport, buffering mechanical stress, suppressing side reactions, and stabilizing interfaces through multilevel strategies. These strategies include nanostructuring and microstructural design, lattice regulation, carbon-based composites, and interface engineering. Through synergistic effects, these strategies effectively enhance the cycling stability, rate capability, and reaction reversibility of iron-based fluorides. Finally, we discuss the key issues facing the future commercialization of iron-based fluorides, aiming to provide design insights for their further development.