Engineering a synergistic La-MOF-OH/PEO interfacial layer toward high-performance all-solid-state sodium metal batteries

Sodium-based all-solid-state metal batteries (ASSMBs) are promising alternatives to traditional lithium-based batteries. However, interfacial mismatch remains a long-standing challenge between Na metal nodes and solid-state electrolytes (SSEs), such as Na/NASICON interface, motivating extensive interface engineering efforts. Interfacial modification using flexible polymer composites with fillers has been investigated to mitigate this issue. Despite these advances, current filler designs predominantly target polymer disordering (e.g., PEO), seriously undermining the multifunctional potential of fillers. In this work, a novel MOF (La-MOF-OH) was designed by judiciously selecting metal nodes (La³⁺) and linkers (H₃chel). It was blended with PEO to form an La-MOF-OH/PEO layer (LMPL) on NASICON, constructing the NASICON-LMPL. Therein, La-MOF-OH acts as multifunctional active fillers by enriching Na⁺, providing low-barrier pathways for Na⁺ migration, and lowering crystallinity of PEO. Na|NASICON-LMPL|Na symmetric cells with a high critical current density (CCD) of 1.8 mA cm⁻² sustain stable cycling for over 2000 h at 0.1 and 0.5 mA cm⁻². Na|NASICON-LMPL|Na₃V₂(PO₄)₃(NVP) full cells deliver 106.4 mAh g⁻¹ at 0.1 C and retain 92.8% capacity after 100 cycles at 1 C. This work underscores the significance of the proposed design principles for MOF fillers, combined with interfacial engineering, as a versatile and general strategy for developing high-performance.