Comprehensive Study of PAN-NaBF4 Solid Polymer Electrolytes: Insights Into Optical, Structural, Thermal, Electrical, and Electrochemical Properties for Sodium-Ion Batteries

This research explores the use of solid polymer electrolytes (SPEs) as a conductive medium for sodium ions in sodium-ion batteries, presenting a possible alternative to traditional lithium-ion battery technology. The researchers prepare SPEs with varying molecular weight ratios of polyacrylonitrile (PAN) and sodium tetrafluoroborate (NaBF₄) using a solution casting method with dimethyl formamide as the solvent. Through optical absorbance measurements, we identified the PAN:NaBF₄ (80:20) SPE composition as having the lowest energy band gap value (4.48 eV). This composition also exhibits high thermal stability based on thermogravimetric analysis results. Electrochemical impedance spectroscopy reveals an ionic conductivity of 1.02 × 10⁻⁴ S cm⁻¹ for the PAN:NaBF₄ (80:20) blend at ambient temperature. Additionally, linear sweep voltammetry demonstrates its good electrochemical stability up to 3.22 V. We assemble a primary sodium-ion battery using the optimal SPE composition (Na/(PAN + NaBF₄)/(I₂ + C + electrolyte)). This battery achieves an open-circuit voltage of 2.83 V and displays promising discharge performance.