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 Na_3.4Zr_1.8Mn_0.2Si₂PO₁₂ 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.