Ultrathin Li_1.3Al_0.3Ti_1.7(PO₄)₃-Based Flexible Solid Electrolyte for All-Solid-State Lithium Batteries

NASICON-type solid electrolytes are highly attractive for solid-state lithium batteries due to their superior ionic conductivity and low cost. However, practical implementation remains severely limited by their inherent brittleness, poor solid-solid contact, and severe side reactions with lithium metal. Herein, we report a flexible Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP)-based composite solid electrolyte film fabricated via an in-situ polymerization strategy. This film achieves an exceptionally high LATP loading of 90 wt% within a minimal thickness of 20 μm, ensuring outstanding thermal stability and safety. Crucially, the composite electrolyte delivers a competitive roomtemperature ionic conductivity of 1.5 × 10^-4 S cm^-1 and an expansive electrochemical window exceeding 5.1 V. Consequently, symmetric Li||Li cells demonstrate excellent interfacial stability, sustaining over 600 hours of steady cycling at 60 °C and 0.1 mA cm^-2. Furthermore, full cells paired with LFP and NCM811 cathodes display superior long-term cyclability and rate performance.