Terminally Fluorinated Polyimide Interphase for Durable Lithium‐Rich Layered Oxide Cathodes

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ABSTRACT Lithium‐rich layered oxides (LLOs) deliver high energy density via coupled cationic/anionic redox, but high‐voltage oxygen activation generates radical‐rich interfaces that accelerate electrolyte decomposition, surface reconstruction, and mechanical failure. Although polyimide serves as an oxidation‐resistant interphase on LLO cathodes, its durability is limited by labile termini vulnerable to reactive oxygen species, whereas backbone fluorination compromises ionic transport. In this study, a terminally fluorinated polyimide (FPI) interphase is constructed on LLOs (LLO‐FPI) by introducing electron‐withdrawing ─CF 3 termini to elevate the interfacial electronic barrier, thereby mitigating oxidative attack and oxygen release while preserving backbone integrity. Terminal fluorination suppresses radical‐mediated degradation and parasitic oxidation, while the high‐modulus FPI interphase constrains stress‐driven particle cracking without sacrificing Li + kinetics. Consequently, LLO‐FPI exhibits exceptional long‐term cycling stability, retaining 80.8% capacity after 1000 cycles. A Si/C||LLO‐FPI pouch cell delivers 409 Wh kg −1 with 90.1% capacity retention over 100 cycles. These findings identify terminal fluorination as a versatile strategy for durable high‐energy‐density batteries.

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