Engineering Composite Solid-State Electrolyte with Multiple Ionic Channels for Stable Sodium Metal Batteries

Xin Wang¹Jiayang Li^1*Xinghan Li¹Hyojoo Lee¹Ziwei Tong¹Wei Kong Pang^1*Bernt Johannessen^1,2*

• ¹University of Wollongong, Wollongong, Australia
• ²Australian Nuclear Science and Technology Organisation, Sydney, Australia

Composite solid-state electrolytes (CSSEs) represent a promising pathway toward advanced sodium metal batteries (SMBs), which are crucial for meeting the demand for higher energy density in electric vehicles and devices. However, the overall performance of SMBs, particularly in terms of safety and stability, remains below expectations due to limited ionic conductivity and interfacial uneven Na deposition. Herein, we develop an innovative composite solid-state electrolyte system that selects NASICON-type Na3.7Zr1.45Sc0.4Mg0.15Si2PO12 (NSMZSP) as an inorganic filler for incorporation into a polyvinylidene fluoride (PVDF) organic matrix. The optimized PVDF@NSMZSP CSSE creates multiple ionic transport channels along the PVDF, NSMZSP, and PVDF/NSMZSP interfaces, thus effectively promoting Na+ transport dynamics and optimizing the electrolyte/electrodes interface compatibility. An exceptional ionic conductivity of 5.5×10-4 S cm-1 at room temperature and a high Na+ transference number of 0.56 can be achieved accordingly. Full Na//Na3V2(PO4)3 cells employing this electrolyte deliver excellent rate capability and long-term cycling stability, maintaining a high initial discharge capacity of 95.7 mAh g-1 at 0.5 C, with a capacity retention of 95% after 200 cycles. This work demonstrates a promising CSSE system with fast ionic transportation, improved interfacial stability and sustainable cycle life, inspiring the construction of next-generation SMBs with well-designed CSSEs in the field of energy storage technology.