Electrochemically induced crystalline-to-amorphization transformation in sodium samarium silicate solid electrolyte for long-lasting all-solid-state sodium metal batteries

Abstract Exploiting solid electrolyte (SE) materials with high ionic conductivity, good interfacial compatibility, and ultraconformal contact with electrode are essential for solid-state sodium metal batteries (SSBs). Here we report a crystalline Na5SmSi4O12 SE which features high room-temperature ionic conductivity of 2.90×10-3 S cm-1 and a low activation energy of 0.15 eV. All-solid-state symmetric cell with Na5SmSi4O12 delivers excellent cycling life over 800 h at 0.15 mA h cm-2 and high critical current density of 1.4 mA cm-2. Such excellent electrochemical performance is attributed to an electrochemically induced in-situ crystalline-to-amorphous (CTA) transformation propagating from the interface to the bulk during repeated deposition and stripping of sodium, which lead to faster ionic transport and superior interfacial properties. Impressively, the Na3V2(PO4)3||Na5SmSi4O12||Na SSBs achieves a remarkable cycling performance over 4000 cycles (6 months) with no capacity loss. These results not only identify Na5SmSi4O12 as a promising SE, but also emphasize the potential of the CTA transition as a promising mechanism towards long-lasting SSBs.