Mn Dopant Na3Zr2Si2PO12 with Enhanced Ionic Conductivity for Quasi-Solid-State Sodium–Metal Battery

As a promising solid electrolyte, the NASICON-type Na3Zr2Si2PO12 holds excellent application in solid-state sodium-ion batteries, which are an alternative to lithium batteries. However, its insufficient conductivity is one of the key factors impeding its applications. Herein, we report Mn2+-doped Na3Zr2Si2PO12, demonstrating enhanced ionic conductivity and electrochemical properties. We systematically investigate the effect of doping content on the ionic conductivity. The results show that Na3.4Zr1.8Mn0.2Si2PO12 has an extremely high room-temperature ionic conductivity of 3.3 mS cm-1, which is 4 times that of undoped Na3Zr2Si2PO12. According to the Meyer-Nedle rule, it can be known that as the activation energy decreases, the ionic conductivity shows a gradually increasing trend. Additionally, the Na symmetric batteries using Mn2+-doped Na3Zr2Si2PO12 exhibit improved cycling performance. The quasi-solid-state sodium-metal battery using Na3V2(PO4)3 achieves a high discharge specific capacity of 91.3 mAh g-1 at 0.1C, with a high capacity retention of 92.2% after 260 cycles, far surpassing the counterpart based on undoped Na3Zr2Si2PO12. This work provides an effective strategy for enhancing the performance of Na3Zr2Si2PO12 for its application in sodium-metal batteries.