固体电解质的低离子电导率及固体电解质与固态电极之间较差的界面可靠性是阻碍固态钠电池（SSSB）应用的两大紧迫挑战。本文采用简单的两步固相法合成了名义成分为Na_3+2xZr_2‒xMg_xSi₂PO₁₂ 的钠（Na）超离子导体（NASICON）型固体电解质，其中在25 ℃时Na_3.3Zr_1.85Mg_0.15Si₂PO₁₂（x=0.15, NZSP-Mg_0.15)表现出了3.54 mS∙cm^‒1的最高离子电导率。通过深入研究，本文证实晶界成分在决定NASICON总离子电导率中起着至关重要的作用。此外，由于文献中缺乏关于NASICON是否能够提供足够的阳极电化学稳定性来实现高压固态钠电池的研究，我们首先使用了高压Na₃(VOPO₄)₂F (NVOPF)正极来验证其与优化后的NZSP-Mg_0.15固体电解质之间的兼容性。通过比较不同配置（低压阴极与高压阴极、液态电解质与固体电解质）电池的电化学性能，以及对循环后的NZSP-Mg_0.15进行X射线光电子能谱（XPS）评估，结果表明，NASICON固体电解质在高电压下不够稳定，这证明了研究NASICON固体电解质和高压阴极之间界面的重要性。此外，通过将NZSP-Mg_0.15 NASICON 粉末涂在聚乙烯（PE）隔膜（PE@NASICON）上，形成了2.42 A∙h 的碳|PE@NASICON|NaNi_2/9Cu_1/9Fe_1/3Mn_1/3O₂ 非水系钠离子电池，其具有出色的循环性能，在2000 周循环后容量保持率为88%，从而证明涂有NASICON型固体电解质的隔膜具有高可靠性。

The low ionic conductivity of solid-state electrolytes (SSEs) and the inferior interfacial reliability between SSEs and solid-state electrodes are two urgent challenges hindering the application of solid-state sodium batteries (SSSBs). Herein, sodium (Na) super ionic conductor (NASICON)-type SSEs with a nominal composition of Na_3+2xZr_2–xMg_xSi₂PO₁₂ were synthesized using a facile two-step solid-state method, among which Na_3.3Zr_1.85Mg_0.15Si₂PO₁₂ (x = 0.15, NZSP-Mg_0.15) showed the highest ionic conductivity of 3.54 mS∙cm^–1 at 25 °C. By means of a thorough investigation, it was verified that the composition of the grain boundary plays a crucial role in determining the total ionic conductivity of NASICON. Furthermore, due to a lack of examination in the literature regarding whether NASICON can provide enough anodic electrochemical stability to enable high-voltage SSSBs, we first adopted a high-voltage Na₃(VOPO₄)₂F (NVOPF) cathode to verify its compatibility with the optimized NZSP-Mg_0.15 SSE. By comparing the electrochemical performance of cells with different configurations (low-voltage cathode vs high-voltage cathode, liquid electrolytes vs SSEs), along with an X-ray photoelectron spectroscopy (XPS) evaluation of the after-cycled NZSP-Mg_0.15, it was demonstrated that the NASICON SSEs are not stable enough under high voltage, suggesting the importance of investigating the interface between the NASICON SSEs and high-voltage cathodes. Furthermore, by coating NZSP-Mg_0.15 NASICON powder onto a polyethylene (PE) separator (PE@NASICON), a 2.42 A∙h non-aqueous Na-ion cell of carbon|PE@NASICON|NaNi_2/9Cu_1/9Fe_1/3Mn_1/3O₂ was found to deliver an excellent cycling performance with an 88% capacity retention after 2000 cycles, thereby demonstrating the high reliability of a separator coated with NASICON-type SSEs.