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 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 SSEs with NASICON-coated separator.

固态电解质（SSEs）的低离子电导率和SSEs与固态电极之间较差的界面可靠性是阻碍固态钠电池（SSSBs）应用的两大紧迫挑战。在此，采用简便的两步固相法合成了标称组成为 Na _{3+2 x} Zr _{2– x} Mg _x Si ₂ PO ₁₂的钠 (Na) 超离子导体 (NASICON) 型 SSE ，其中Na _3.3 Zr _1.85 Mg _0.15 Si ₂ PO ₁₂ ( x  = 0.15, NZSP-Mg _0.15)在 25 °C 下显示出 3.54 mS∙cm ^-1的最高离子电导率。通过深入研究，证实晶界的成分在决定 NASICON 的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 是否可以提供足够的阳极电化学稳定性来实现高压 SSSB，我们首先采用高压 Na ₃ (VOPO ₄ ) ₂ F (NVOPF) 正极来验证其兼容性使用优化的 NZSP-Mg _0.15上证所。通过比较具有不同配置（低压阴极与高压阴极、液体电解质与 SSE）的电池的电化学性能，以及对循环后的 NZSP-Mg _0.15进行 X 射线光电子能谱评估，证明了NASICON SSEs 在高压下不够稳定，这表明研究 NASICON SSEs 和高压阴极之间的界面的重要性。此外，通过将 NZSP-Mg _{0.15 NASICON 粉末涂覆在聚乙烯 (PE) 隔板 (PE@NASICON) 上，形成了一个 2.42 A∙h 的碳|PE@NASICON|NaNi 2/9} Cu _1/9非水钠离子电池铁_1/3锰_1/3 O ₂被发现具有出色的循环性能，在 2000 次循环后具有 88% 的容量保持率，从而证明了具有 NASICON 涂层隔膜的 SSE 的高可靠性。