Flexible composite solid electrolyte with 80 wt% Na3.4Zr1.9Zn0.1Si2.2P0.8O12 for solid-state sodium batteries

Composite solid electrolyte (CSE) with high ceramic content has received extensive attention due to the combined advantages of ceramic electrolyte and flexible polymer component as well as superior thermal stability and mechanical properties. However, high ionic conductivity , desired flexibility and excellent electrolyte-electrode interfacial contact are huge challenges. Herein, a flexible, non-flammable and high ion conductive NASICON CSE with 80 wt% Na 3.4 Zr 1.9 Zn 0.1 Si 2.2 P 0.8 O 12 particles in polyethylene oxide is realized through coupling with trace amount of ionic liquid into the CSE. The resultant NASICON CSE delivers high ionic conductivity of 1.48 × 10 −4  S cm −1 at 25 °C, outstanding thermal stability and good interfacial stability against sodium metal. Benefiting from these merits, the assembled Na 3 V 2 (PO 4 ) 3 //Na solid-state sodium batteries demonstrate excellent rate performances and cycling stability with a capacity retention of 90.0% after 150 cycles at 0.5 C under 60 °C. The Na 3 V 2 (PO 4 ) 3 //Na battery further exhibits an initial discharge capacity of 109.4 mAh g −1 with a capacity retention of 85.4% after 150 cycles at 0.2 C under 25 °C. Moreover, the Na 3 V 2 (PO 4 ) 3 //Na pouch battery exhibits impressive flexibility and safety. This work provides a promising strategy to realize flexible, non-flammable and high ion conductive NASICON CSE with high content of NASICON component for solid-state sodium batteries.