Interface‐Targeting Integrated Sandwich‐Structured Na ₃ Zr ₂ Si ₂ PO ₁₂ Composite Electrolyte for Ultra‐Long Cycle Life Sodium Metal Batteries

Na₃Zr₂Si₂PO₁₂ (NZSP) has stimulated considerable attention due to its remarkable ionic conductivity and exceptional chemical/electrochemical stability. However, an unstable electrolyte/electrode interface and large interface resistance severely restricted its practical application. To settle this issue, an interface-targeting integrated sandwich-like NZSP composite electrolyte was constructed by designing an artificial interface layer on both the anode and cathode sides. The uniformly deposited SbF₃ layer on the anode side of NZSP instantly formed a Na_xSb/NaF-rich conductive layer during discharging, which effectively suppressed the growth of Na dendrites. The flexible PVDF layer on the cathode side of NZSP mitigated volume expansion/contraction and thus enhanced the poor solid-solid interfacial contact. Befitting the unique interface design, the Na/SbF₃-NZSP-SbF₃/Na symmetric cells demonstrated a critical current density of up to 1.9 mA cm^-2 and achieved ultra-stable plating/stripping cycling over 2600 h at 0.1 and 0.2 mA cm^-2, respectively. Noticeably, the Na₃V₂(PO₄)₃/PVDF-NZSP-SbF₃/Na full cells attained a high capacity retention of 90.0% after 2100 cycles at 0.5 C. Even for a high mass loading of 10.33 mg cm^-2, Na₃V₂(PO₄)₃/PVDF-NZSP-SbF₃/Na has no capacity attenuation over 50 cycles at 0.1 C. This bilateral interface design strategy promotes the utilization of NZSP electrolytes and offers an avenue for the development of solid-state sodium-ion batteries (SIBs).