Enhancing Interfacial Stability Between NASICON‐Type Solid‐State Electrolyte and Lithium Metal Anode via Multifunctional Synergistic Interface Engineering

ABSTRACT Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP)‐based all‐solid‐state lithium metal batteries (ASSLMBs) hold exceptional promise for achieving high energy density and excellent safety, yet their practical application is severely hindered by critical interfacial issues, including poor contact, side reactions, and dendrite growth. Herein, a flexible multifunctional composite interlayer (PVGa) composed of Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and gallium(III) fluoride (GaF 3 ) is constructed at the LATP/Li interface via a facile solution drop‐casting method. The polymer matrix effectively fills interfacial voids, homogenizes current distribution, and suppresses side reactions, while GaF 3 undergoes in situ alloying with the Li anode to form a uniform and dense LiF/Li x Ga hybrid SEI layer with high ionic conductivity and interfacial energy, guiding homogeneous Li deposition. Benefiting from this synergistic effect, the LATP@PVGa symmetric cell achieves a critical current density of 1.9 mA cm −2 and exhibits stable cycling over 6000 h at 0.1 mA cm −2 and 4500 h at 0.2 mA cm −2 . Moreover, LiFePO 4 full cells retain 86.7% capacity after 1100 cycles at 0.5 C, demonstrating excellent practical application potential. This work provides a novel and effective strategy to address the multifaceted interfacial challenges in LATP‐based ASSLMBs.