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

Abstract Na 3 Zr 2 Si 2 PO 12 (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 SbF 3 layer on the anode side of NZSP instantly formed a Na x Sb/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/SbF 3 ‐NZSP‐SbF 3 /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 Na 3 V 2 (PO 4 ) 3 /PVDF‐NZSP‐SbF 3 /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 , Na 3 V 2 (PO 4 ) 3 /PVDF‐NZSP‐SbF 3 /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).