Mechanically reinforced NASICON electrolytes co-doped with Sc3+ and Mg2+ for dendrite-resistant sodium metal batteries

Both the electrochemical and mechanical properties of solid-state electrolytes are crucial for achieving stable battery performance, while the widely studied NASICON-type electrolytes such as Na 3 Zr 2 Si 2 PO 12 (NZSP) still suffer from poor conductivity and a tendency to Na metal penetration. To address these problems simultaneously, we propose an integrated chemistry-structure-mechanics design principle, in which aliovalent Sc/Mg co-doping (chemistry) regulates lattice framework and grain-boundary evolution (structure), thereby enhancing mechanical robustness (mechanics) without compromising ionic transport. The optimized sample (Na 3.4 Zr 1.7 Sc 0.2 Mg 0.1 Si 2 PO 12 ) achieves a high room-temperature conductivity of 1.26 × 10 −3  S cm −1 and a 25% increase in hardness compared with the Mg-free analogue. The solid-state cell assembled with this electrolyte (Na/Na 3.4 Zr 1.7 Sc 0.2 Mg 0.1 Si 2 PO 12 /Na 3 V 2 (PO 4 ) 3 ) shows excellent cycling stability in a wide temperature range of 0-80 °C, and retains 90% of its initial capacity after 440 cycles at 30 °C and 1C. These results demonstrate that aliovalent co-doping to concurrently optimize lattice chemistry and ceramic microstructure is an effective route to high-performance NASICON electrolytes.