Copper-doped metal-organic framework-74 solid-state electrolytes for high performance all-solid-state sodium metal batteries.

Rechargeable solid sodium metal batteries are attractive by virtue of their high energy density and cost-effectiveness. However, the inefficient Na transport dynamics and short lifepan hinder the practical application of solid sodium battery. Mg-MOF-74 nanomaterials have emerged as promising candidates for solid-state electrolytes because of their homogeneous porous structure and highly exposed metal sites. Nonetheless, the Na conductivity of pristine Mg-MOF-74 solid-state electrolytes is limited by sluggish ion movement. In this study, we successfully developed a series of bimetallic MOFs, specifically CuMg-MOF-74, by introducing copper doped metal to Mg-MOF-74. This metal-doped MOF electrolytes possess excellent Na transport and enhanced electrochemical stability in solid sodium metal batteries. The bimetallic sites of CuMg-MOF-74 deliver a superior capability to anchor anion ClO than single Mg sites in Mg-MOF-74, as validated by density functional theory calculation. Benefiting from that, CuMg-MOF-74 electrolytes substantially increase the ionic conductivity to 3.18 × 10 S cm and the Na transference number to 0.86 at room temperature. Additionally, NaV(PO)|CuMg-MOF-74|Na cells demonstrated a high specific capacity of 104.5 mAh g at 1C, with an impressive capacity retention rate of 91 %. Overall, this study delivers a viable method to optimize MOF materials for improved Na conductivity in future applications.