Enhanced ionic conductivity of Ce-doped Na ₃Zr ₂Si ₂PO ₁₂ electrolyte for achieving superior performance of solid-state sodium batteries

Solid-state sodium batteries (SSSBs) are gaining significant attention for their potential in electrochemical energy storage. However, the development of SSSBs is hindered by the low ionic conductivity of sodium-ion solid electrolytes (SSEs). Herein, Ce with a relatively large ionic radius is employed to replace Zr in Na₃Zr₂Si₂PO₁₂ (NZSP), aiming to increase the ionic conductivity of the SSEs. Through structural analysis and theoretical calculations, it is inferred that Ce doping is favorable for stabilizing phases with higher ionic conductivity, increasing the Na⁺ concentration via the substitution of Zr⁴⁺ with Ce³⁺, and facilitating the generation of a densified microscopic morphology. The Ce-doped NZSP achieves a high room-temperature conductivity of 2.08 mS·cm⁻¹ and good interfacial compatibility with Na metal. Furthermore, the assembled Na₃V₂(PO₄)₃ cell based on Ce-doped NZSP maintains a capacity of 111.18 mAh·g⁻¹ at 0.5 C after 200 cycles, with a high retention of 98.06%.