Ferroelectric Low-Tortuosity Separators for Dendrite-Free Solid-State Lithium Metal Batteries

Lithium metal batteries face uncontrollable dendrite growth and interfacial instability. While solid polymer electrolytes (SPEs) via in situ polymerization offer a promising solution, they require functional separators-yet commercial ones suffer from tortuous pores, poor wettability, and low thermal stability. Here, we engineer ferroelectric BaTiO₃-coated track-etched membranes (BTEMs) with vertically aligned channels to address these challenges. The low-tortuosity architecture shortens Li⁺ diffusion pathways, while ferroelectric polarization homogenizes electric field and Li⁺ flux. Coupled with in situ polymerized poly(1,3-dioxolane) (PDOL) electrolyte, the BTEMs-based SPE achieves exceptional ionic conductivity (σ = 0.12 mS cm^-1) and transference number ( $t_{L{i}^{+}}$ = 0.73). The resulting solid-state batteries deliver >1000 h of stable Li plating/stripping and Li||LiFePO₄ full cells retaining 80.2% capacity after 260 cycles at 0.4 C. The pouch cell delivers a discharge capacity of 5.83 mAh and remains operational even after folding or cutting. Both experimental and computational studies confirm that the low-tortuosity BTEMs shorten the Li⁺ transport pathway and drive electric field redistribution, thereby achieving uniform Li deposition. Overall, this work establishes a paradigm of geometrically engineered ferroelectric separators that concurrently resolve ionic transport bottlenecks and dendrite propagation, paving the way for next-generation LMBs with high performance and safety.