A New Route to High‐Performance Halide‐Based Solid‐State Batteries: Perfluoropolyether Enables Ion Transport Expansion and Interfacial Protection

ABSTRACT Halide‐based solid‐state batteries (SSBs) promise high energy density and inherent safety but are constrained by sluggish Li + transport and interfacial instabilities in composite cathodes. Filling voids with fluid organic could provide a compliant interface contact. Yet, halide SSEs are highly reactive with organics. Here, we systematically assess the chemical compatibility of functional organic molecules with halide SSEs and identify perfluoropolyether (PFE) as an exceptionally stable functional organic toward the cost‐effective halide SSEs Li 1.75 ZrCl 4.75 O 0.5 (LZCO). Owing to its low volatility, high wettability, and intrinsic nonflammability, PFE is readily integrated into composite cathodes via dry‐electrode processing without compromising the safety of SSBs. During cycling, PFE scavenges deintercalated Li + and forms an in situ fluoropolyether‐LiF hybrid cathode electrolyte interphase (CEI). This conformal CEI converts discrete point contacts between LiNi 0.82 Co 0.14 Mn 0.04 O 2 (Ni82) and LZCO into continuous areal contacts. Rapid Li + transport through the highly conductive CEI reactivates the previously isolated Ni82 particles. Concurrently, the robust CEI suppresses parasitic reactions including electrolyte oxidation, O 2 evolution, rock‐salt phase formation, Li/Ni mixing, and particle cracking of Ni82. Cathodes containing PFE deliver 206 mAh g −1 at 0.1C and exhibit 83% capacity retention after 1500 cycles at 0.5C. Pouch‐cell validation underscores the scalability of PFE for commercially viable SSBs.