A Fluorinated 3D Interphase With Built‐In Si‐Gradient Lithiophilicity Enables Spatially Adaptive Li Deposition for Stable Li Metal Anode

ABSTRACT Li metal anodes, sought after for next‐generation high‐energy batteries, are severely hindered by dendritic growth and an unstable solid electrolyte interphase (SEI). Here, we design a fluorinated 3D artificial SEI with a built‐in vertical Si‐gradient lithiophilicity (3D F‐SiG SEI) via in situ copolymerization of hexafluorobutyl methacrylate and 2,4,6,8‐tetramethyl‐2,4,6,8‐tetraethynylcyclotetrasiloxane. Critically, this crosslinking reaction proceeds exclusively under the catalytic action of the Li metal substrate, ensuring seamless interfacial integration. The resulting porous SEI generates a continuous lithiophilicity gradient that homogenizes Li + flux, enforces “bottom‐up” pore‐filling deposition, and buffers volume fluctuations. Simultaneously, the F/Si‐rich chemistry promotes in situ formation of a stable LiF‐enriched Si‐based SEI, which reduces the nucleation overpotential and accelerates interfacial kinetics. The modified anode delivers an average Coulombic efficiency of 99.4% in half cells and ultralong cycling stability over 3500 h in symmetric cells. Full cells paired with LiFePO 4 and high‐nickel NCM cathodes exhibit superior capacity retention and rate capability even under high mass loading. This work provides a blueprint for simultaneously engineering interfacial deposition, buffering volume fluctuations, and enhancing air stability in practical Li metal anodes.