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 Na3Zr2Si2PO12 solid electrolyte limit the practical application of all-solid-state sodium batteries. Herein, the optimized Na3.4Mg0.1Zr1.9Si2.2P0.8O12 electrolyte is obtained by simultaneously substituting the Zr4+ with Mg2+ and P5+ with Si4+ through solid-state reaction. The Na3.4Mg0.1Zr1.9Si2.2P0.8O12 electrolyte has superior room temperature ionic conductivity of 3.6 × 10−3 S cm−1, which is 17 times higher than that of pristine Na3Zr2Si2PO12. No short circuit of the Na/Na3.4Mg0.1Zr1.9Si2.2P0.8O12/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 Na3.4Mg0.1Zr1.9Si2.2P0.8O12 electrolyte is further employed in two all-solid-state sodium batteries. The Na3V2(PO4)3/Na3.4Mg0.1Zr1.9Si2.2P0.8O12/Na all-solid-state sodium battery maintains a discharge capacity of 93.3 mAh g−1 at 0.1C after 50 cycles, and the FeS2/Na3.4Mg0.1Zr1.9Si2.2P0.8O12/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 Na3Zr2Si2PO12. 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.