Electrochemical Performance of PEO–NaNO ₃ –NASICON Polymer–Ceramic Composite Electrolytes: The Roles of Composition and Particle Size of Ceramic Filler

Polymer–ceramic composite electrolytes (CEs) integrate the flexibility of a polymer electrolyte (PE) and the high ionic conductivity of a ceramic electrolyte. Thus, CEs are considered one of the promising electrolytes for the development of solid-state sodium rechargeable batteries. Here, we report the ionic conductivity and electrochemical cell performance of solid CEs comprising PEO–NaNO3 (with fixed EO/Na+ = 15:1) polymer electrolyte (PE) and highly conducting NASICON ceramic of Na3.4Zr1.9Zn0.1Si2.2P0.8O12 (NZZSP) with 0–75 wt %. The (PE)–(60 wt % Na3.4Zr1.9Zn0.1Si2.2P0.8O12) composite electrolyte exhibits high room temperature (RT) conductivity of 2.2 × 10–4 S cm–1. Results of the structural and thermal characterizations of CEs, conducted using X-ray diffraction (XRD), solid-state NMR spectroscopy, positron annihilation lifetime spectroscopy (PALS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC), are presented. The ionic conduction property of CEs was investigated by electrochemical impedance spectroscopy (EIS), and an electrochemical test of the optimized CE was conducted with cyclic voltammetry and galvanostatic cycling. The ionic transport property of (PE)–(60 wt % Na3.4Zr1.9Zn0.1Si2.2P0.8O12) CE has been compared with (PE)–(60 wt % Na3.4Zr1.9Nb0.1Si2.4P0.6O12) and (PE)–(60 wt % Na3.4Zr1.8Sc0.2Si2.2P0.8O12) CEs. The role of the NASICON composition, geometry, and size of the ceramic filler on the ionic conductivity has been revealed. The symmetrical cells of Na|PE–60 wt % Na3.4Zr1.9Zn0.1Si2.2P0.8O12|Na and Na|PE–60 wt % Na3.4Zr1.9Nb0.1Si2.4P0.6O12|Na show a promising long-term and stable cycling performance at RT.