High ionic conductivity and dendrite-resistant NASICON solid electrolyte for all-solid-state sodium batteries

The low ionic conductivity and poor dendrites suppression capability of Na 3 Zr 2 Si 2 PO 12 solid electrolyte limit the practical application of all-solid-state sodium batteries . Herein, the optimized Na 3.4 Mg 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 electrolyte is obtained by simultaneously substituting the Zr 4+ with Mg 2+ and P 5+ with Si 4+ through solid-state reaction. The Na 3.4 Mg 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 electrolyte has superior room temperature ionic conductivity of 3.6 × 10 −3  S cm −1 , which is 17 times higher than that of pristine Na 3 Zr 2 Si 2 PO 12 . No short circuit of the Na/Na 3.4 Mg 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 /Na symmetric battery is observed up to 2.0 mA cm −2 , and the symmetric battery displays stable sodium plating/stripping cycles for over 2000 h at 0.1 mA cm −2 and 300 h at 1.0 mA cm −2 . The resultant Na 3.4 Mg 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 electrolyte is further employed in two all-solid-state sodium batteries. The Na 3 V 2 (PO 4 ) 3 /Na 3.4 Mg 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 /Na all-solid-state sodium battery maintains a discharge capacity of 93.3 mAh g −1 at 0.1C after 50 cycles, and the FeS 2 /Na 3.4 Mg 0.1 Zr 1.9 Si 2.2 P 0.8 O 12 /Na all-solid-state sodium battery delivers a discharge capacity of 173.1 mAh g −1 at 0.1C after 20 cycles, which are significantly enhanced compared with those based on pristine Na 3 Zr 2 Si 2 PO 12 . This strategy provides an efficient method to prepare optimized NASICON solid electrolytes with high ionic conductivity and excellent dendrites suppression capability and promotes the practical application of all-solid-state sodium batteries.