Structural and Electrical Properties of Plasticized CS:PVP:KNO 3 :Al 2 O 3 Nanocomposite Polymer Electrolytes

A series of chitosan–polyvinylpyrrolidone (CS–PVP) blend nanocomposite polymer electrolytes containing KNO3 salt and Al2O3 nanoparticles were prepared with varying glycerol plasticizer content to investigate their structural and electrical properties. X-ray diffraction (XRD) patterns show that increasing glycerol disrupts the polymer crystallinity, as evidenced by broader diffraction peaks and a significant decrease in crystalline fraction. Fourier-transform infrared (FTIR) spectroscopy reveals that glycerol introduces new hydrogen-bonding interactions with the polymer and salt: the broad O–H stretching band (∼3300 cm−1) shifts and broadens with glycerol, reflecting altered polymer H-bonding, and shifts in amide and carbonyl regions confirm enhanced polymer–salt–plasticizer complexation. Impedance spectroscopy indicates a dramatic reduction in bulk resistance and an ∼179-fold increase in room-temperature ionic conductivity, from (4.87 ± 0.24) ×10−9 to (8.70 ± 0.43) ×10−7 S/cm, with glycerol. Dielectric measurements show that both the dielectric constant (ε′) and loss (ε″) at low frequencies rise significantly with glycerol, reflecting increased space-charge polarization and ion mobility. Modulus analysis indicates suppressed electrode polarization and a transition from dual to single semicircles in the Cole–Cole plots with more glycerol. The pronounced improvements suggest that the glycerol-plasticized CS–PVP:KNO3:Al2O3 system is a promising candidate for potassium-ion solid-state battery electrolytes.