Enhancing ionic transport in sodium bromide doped tamarind seed polysaccharide solid polymer electrolytes

Biopolymer electrolyte films were prepared by doping Tamarind Seed Polysaccharide (TSP) with different weight ratios of Sodium Bromide (NaBr) (80:20, 70:30, 60:40 & 50:50 wt%) via solution casting technique. TSP is an eco-friendly and biodegradable polymer, and can support ion transport, and NaBr serves as eco-friendly source of Sodium. Together, they offer simple and low-cost approach for developing safer solid-state Sodium-ion batteries, which serve as alternative dependence on Lithium. Fourier Transform infrared spectroscopy (FTIR) confirmed complexation between TSP and NaBr through systematic shifts in O–H, CH 2 , carbonyl and C–O stretching bands. X-ray Diffraction (XRD) showed progressive reduction in the degree of crystallinity with increasing NaBr content, with TSP:NaBr (60:40 wt%) exhibiting lowest crystallinity and highest amorphous nature, substantiated by smooth, homogeneous surface morphology observed by the results from Scanning Electron Microscopy (SEM). Alternating Current (AC) impedance spectroscopy showed that the biopolymer film with composition TSP:NaBr (60:40 wt%) exhibited highest ionic conductivity value of 1.13 × 10 −4 S cm −1 at 303 K, increased to 3.39 × 10 −4 S cm −1 at 373 K, and followed Arrhenius behaviour with an activation energy of 0.089 eV. Wagner’s polarization technique confirmed that the transport mechanism within the electrolyte is predominantly ionic in nature with ionic transference number, tion reported to be 0.99, with minimal electronic contribution, and Linear Sweep Voltammetry (LSV) indicated an electrochemical stability window of 2.52 V for TSP:NaBr (60:40 wt%) composition. A primary battery was fabricated using the TSP:NaBr (60:40 wt%) electrolyte, sodium metal anode, and Iodine-Carbon Composite cathode, delivering an open-circuit voltage of 2.1 V and a short-circuit current of 0.9 mA, with stable discharge behaviour. These findings suggest that TSP-based biopolymer electrolytes with optimized NaBr dopant ratios are promising, eco-friendly candidates for sodium-ion-conducting solid-state battery applications.