Fabrication of spherical precursor-based green sheets for the preparation of high-performance partially fluorinated NASICON electrolytes in solid-state sodium batteries

초록

For the realization of practical solid-state sodium-ion batteries, the development of solid electrolytes with high ionic conductivity and scalable manufacturing processes is essential. In this study, spherical precursor powders for NASICON-type solid electrolytes (Na3.1Zr1.55Si2.3P0.7O11) were synthesized via a spray drying and combined with a polytetrafluoroethylene (PTFE) binder to produce flexible and scalable green sheets. These were subsequently sintered through a solid-state process with shortened sintering time to obtain high-performance NASICON electrolytes. The optimized NASICON electrolyte prepared with 0.5 wt% PTFE exhibited a high relative density of 99.6% and ionic conductivity of 1.93 x 10-3 S cm-1 at room temperature. Notably, PTFE decomposition during sintering induced partial fluorination of NASICON, which contributed to interfacial stabilization and suppression of sodium dendrite growth. As a result, the optimized NASICON demonstrated a high critical current density of 1.5 mA cm-2 and stable Na plating/stripping behavior at 1.0 mA cm- 2 for over 1000 h. Furthermore, the solid-state sodium battery, composed of a Na3V2(PO4)3 (NVP) cathode and a Na metal anode, delivered an initial discharge capacity of 109.1 mAh g-1 at 0.01 A g-1 and retained 94.8% of its capacity after 100 cycles at 0.1 A g- 1. This work highlights an effective dry-processing strategy for the fabrication of highperformance Na-based solid electrolytes and provides a viable pathway toward the practical realization of large-area solid-state sodium batteries.

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