Perovskite Fluoride Anode Stabilized via Ligand‐Field Engineering for High‐Performance Lithium‐Ion Batteries

Abstract

ABSTRACT Perovskite fluorides (AMF 3 , A = alkali metal ions; M═Fe, Mn, etc.) have emerged as promising high‐capacity anode materials for lithium‐ion batteries (LIBs). However, their practical application is hindered by an intrinsic coupling of structural degradation and interfacial instability, primarily arising from the dynamic evolution of transition‐metal (TM) electronic states during cycling. Conventional extrinsic modification strategies have proven inadequate in addressing this intrinsic limitation. Herein, we propose a universal ligand‐field engineering strategy to intrinsically regulate the TM electronic environment, with KFeF 3 employed as a representative model system. Isovalent Mn 3+ doping effectively tunes the Fe‐centered ligand field, suppressing Jahn‐Teller distortions and mitigating spin‐state fluctuations. The resulting KFe 0.5 Mn 0.5 F 3 @C composite exhibits outstanding cycling stability, demonstrating negligible capacity decay after 500 cycles at 0.5 A g −1 and an unprecedented capacity retention of 94.65% after 1700 cycles at 1 A g −1 . Theoretical calculations further reveal that Mn doping stabilizes a low‐spin Fe state, which mitigates crystal‐field distortions while simultaneously facilitating the formation of a robust LiF‐rich solid‐electrolyte interphase (SEI). This work offers an electronic‐state‐driven solution to the coupled mechanical‐chemical degradation, thereby establishing ligand‐field regulation as a fundamental design principle for developing advanced conversion‐type electrodes.