Lattice matching governs interfacial kinetics and conversion reversibility in FeF3 cathodes

Abstract

Iron trifluoride (FeF3) conversion-type cathodes generally suffer from bottlenecks including poor interfacial stability and sluggish Li+ transport. Most existing studies have overlooked the critical regulatory effect of the lattice matching relationship between the surface layer and the matrix on electrochemical behaviors. In this work, a lattice-compatible FeF2/FeF3 interface, together with lattice-mismatched CoF3/FeF3 and CuF2/FeF3 interfaces, was in situ constructed on FeF3 substrates. Systematic characterizations confirm that the highly lattice-compatible interface can optimize interfacial transport kinetics, promote the reversible conversion of LiF, and build a stable cathode electrolyte interphase. The modified sample achieves an initial discharge specific capacity of 610 mAh g−1 at 100 mA g−1, and its capacity retention after 100 cycles is 50.0% higher than that of the pristine FeF3. High lattice matching alleviates interfacial strain and reduces the Li+ migration energy barrier, thus improving the reversibility of the conversion reaction. This work proves that lattice-compatible interfacial engineering is one of the vital design guidelines for high-performance FeF3 conversion-type cathodes.