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

As a promising solid electrolyte, the NASICON-type Na 3 Zr 2 Si 2 PO 12 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 Mn 2+ -doped Na 3 Zr 2 Si 2 PO 12, demonstrating enhanced ionic conductivity and electrochemical properties. We systematically investigate the effect of doping content on the ionic conductivity. The results show that Na 3.4 Zr 1.8 Mn 0.2 Si 2 PO 12 has an extremely high room-temperature ionic conductivity of 3.3 mS cm –1, which is 4 times that of undoped Na 3 Zr 2 Si 2 PO 12 . 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 Mn 2+ -doped Na 3 Zr 2 Si 2 PO 12 exhibit improved cycling performance. The quasi-solid-state sodium–metal battery using Na 3 V 2 (PO 4 ) 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 Na 3 Zr 2 Si 2 PO 12 . This work provides an effective strategy for enhancing the performance of Na 3 Zr 2 Si 2 PO 12 for its application in sodium–metal batteries.