Na Plating and Stripping Using Highly Na-Ion Conductive Solid Polymer Electrolytes Based on Polyvinylidene Fluoride and Polyvinylpyrrolidone

Abstract

Solid-state sodium-ion batteries (ss-SIBs) are a promising alternative to commercially available lithium-ion batteries (LIBs) for next-generation energy storage applications. They have lower production costs and are safer than LIBs. Moreover, sodium is more abundant than lithium. The incorporation of solid polymer electrolytes (SPEs) into SIBs has been attracting much more attention due to the easy processability, low costs, safe usability, modification scope, and abundance of polymers. However, SPEs for ss-SIBs with high ionic conductivity and low interfacial resistance between electrolytes and electrodes are lacking. In addition, SPEs face major challenges such as suitable manufacturing methods and the lack of knowledge about low-cost ss-SIBs assembly. Herein, using a facile solution casting process, we have successfully fabricated a high sodium-ion conductive composite SPE film based on polyvinylidene fluoride (PVDF) polymer, polyvinylpyrrolidone (PVP) binder, and NaPF6 salt. A comprehensive characterization has been conducted using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR), Thermogravimetric Analysis (TGA), Raman, and electrochemical impedance spectroscopy techniques to investigate the structural, thermal, and electrochemical performance of the as-prepared SPE films. High ionic conductivity (8.51 x 10-4 S cm-1 and 8.36 x 10-3 S cm-1 at 23°C and 78 °C, respectively) was observed from the SPE. A hybrid symmetric half-cell assembly (Na foil + 20 µL of 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (EC: PC = 1:1) + Carbon-cloth |SPE| Carbon-cloth + 20 µL of 1 M NaClO4 in EC and PC (EC: PC = 1:1) | Na foil) showed excellent Na plating-stripping performance up to 8 mA cm-2 for 100 cycles. In addition, Na+ transfer mechanism in the composite electrolyte has been investigated using impedance and dielectric spectroscopy. The results indicate the promising applicability of SPEs in next-generation high-power rechargeable SIBs.