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

Exploiting solid electrolyte (SE) materials with high ionic conductivity, good interfacial compatibility, and conformal contact with electrodes is essential for solid-state sodium metal batteries (SSBs). Here we report a crystalline Na 5 SmSi 4 O 12 SE which features high room-temperature ionic conductivity of 2.9 × 10 -3  S cm -1 and a low activation energy of 0.15 eV. All-solid-state symmetric cell with Na 5 SmSi 4 O 12 delivers excellent cycling life over 800 h at 0.15 mA h cm -2 and a 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 leads to faster ionic transport and superior interfacial properties. Impressively, the Na|Na 5 SmSi 4 O 12 |Na 3 V 2 (PO 4 ) 3 sodium metal batteries achieve a remarkable cycling performance over 4000 cycles (6 months) with no capacity loss. These results not only identify Na 5 SmSi 4 O 12 as a promising SE but also emphasize the potential of the CTA transition as a promising mechanism towards long-lasting SSBs.