Interface-Stabilized LLTO/PVDF/PE Composite Separator Boosts High-Performance All-Solid-State Lithium Metal Batteries

The development of composite solid electrolytes with high ionic conductivity and superior interfacial stability is crucial for practical all-solid-state lithium metal batteries (ASSLMBs). Herein, a high-performance bilayer composite separator is designed by integrating Li0.33La0.557TiO3 (LLTO) nanofibers into a poly(vinylidene fluoride) (PVDF) matrix, which is coated onto a polyethylene (PE) substrate. The interconnected LLTO nanofibers construct three-dimensional continuous ion-conducting pathways and reduce the crystallinity of the polymer matrix, endowing the optimized separator (with 60 wt % LLTO) with a high ionic conductivity of 5.17 × 10–4 S cm–1, a large lithium-ion transference number (tLi+= 0.81), and a wide electrochemical stability window up to 4.87 V. The unique bilayer architecture, where the LLTO/PVDF layer facilitates rapid Li+ transport and the PE layer ensures interfacial compatibility, enables stable lithium plating/stripping over 500 h and yields a high critical current density of 2.9 mA cm–2. Furthermore, the robust mechanical properties of the separator ensure uniform lithium-ion flux and effectively resist lithium dendrite penetration. When applied in NCM811/Li metal battery, this modified solid-state electrolyte separator enabled remarkable cycling stability (89.8% capacity retention after 200 cycles at 5C) and exceptional rate performance (115.4 mAh g–1 at 5C). This work provides a feasible and effective strategy for designing composite separators toward high-energy-density and dendrite-free ASSLMBs.