Fluorination‐Tuned Covalent Organic Framework Interphases for Controllable LiF Content in Dendrite‐Free Lithium Metal Batteries

Abstract

To tackle the challenge of precisely regulating LiF content within the solid electrolyte interphase (SEI) of high‐energy‐density lithium metal batteries (LMBs), this work presents a fluorination‐gradient design strategy, enabling controllable LiF formation through a covalent organic framework‐based artificial SEI layer (0F‐, 2F‐, and 4F‐COF), and lays the foundation for uncovering the interfacial regulation mechanism. Density functional theory calculations reveal that the electron‐withdrawing F group not only forms an ultra‐low HOMO energy orbital but also promotes the dissociation of LiPF6 via charge delocalization, enabling an oxidation stability of up to 5.4 V (vs. Li+/Li). Consequently, the Li||Li symmetric cell sustains stable cycling for over 6000 h at 1 mA·cm−2, while 4F‐COF@Li cell enables capacity retentions of 90.0% (LiFePO4, 1000 cycles), 80.5% (LiNi0.8Co0.1Mn0.1O2, 300 cycles), and 70.1% (LiNi0.9Co0.09Mo0.01O2, 300 cycles) at 5 C. Ab initio molecular dynamics simulations combined with in situ characterizations further reveal that F‐rich microenvironment of 4F‐COF accelerates LiPF6 dissociation and inhibits dendrite growth while directing the formation of a robust LiF‐rich SEI interphase. Overall, this work establishes precision fluorination of COF‐based artificial SEI layers as a new design strategy for developing safe, high‐rate, and dendrite‐free LMBs.