Glycerol-plasticized chitosan–sorbitol/NaNO 3 electrolytes reinforced with TiO 2 nanofillers: A structural and ionic study

Abstract

This study reports the quantitative impact of glycerol plasticization on the structural and electrochemical performance of chitosan–sorbitol–NaNO₃–TiO₂ (CSNT) solid polymer electrolytes. Films were prepared by solution casting with 3 wt.% TiO₂ and varying glycerol concentrations (11–44 wt.%). FTIR confirmed successful complexation, while XRD revealed a decrease in crystallinity with increasing glycerol, indicating greater amorphousness favorable for ion migration. Electrochemical impedance spectroscopy (EIS) showed that the bulk resistance decreased from 2.61 MΩ to 470 Ω, accompanied by a substantial rise in ionic conductivity from 1.04 × 10⁻⁹ S/cm to 1.2 × 10⁻⁵ S/cm, corresponding to an improvement of more than 5500 times. Dielectric studies revealed that the low-frequency dielectric constant increased from <100 to ∼7200, while the relaxation frequency in tanδ shifted from 0.17 kHz to 30.9 kHz, confirming faster ion dynamics. FTIR deconvolution of the nitrate band further demonstrated a significant increase in the free-ion fraction, yielding enhanced ion transport parameters: carrier density n = 1.33 × 10²² cm⁻³, mobility μ = 1.46 × 10⁻⁹ cm² V⁻¹ s⁻¹, and diffusion coefficient D = 1.46 × 10⁻¹⁰ cm² s⁻¹. These findings demonstrate that glycerol acts as an efficient plasticizer, strongly enhancing ion transport and establishing biopolymer-based electrolytes as promising candidates for advanced energy storage technologies.