Development and characterization of biopolymer electrolyte based on gellan gum for the fabrication of solid-state sodium-ion battery

In the present work, a solid biopolymer membrane (SBPM) with gellan gum (GG) and sodium perchlorate (NaClO4) has been prepared by solution casting method for the fabrication of solid-state sodium-ion battery (SIB). The prepared SBPMs were carried out with various characterization techniques. X-ray diffraction (XRD) method confirms the crystalline/amorphous nature of the prepared biopolymer membranes (BPMs), and the membrane with the composition of 1g GG: 0.6 M.wt% of NaClO4 exhibits high amorphous nature. Fourier transform infrared (FTIR) spectroscopy reveals the complexation between the host biopolymer GG and NaClO4. The glass transition temperature (Tg) of prepared membranes is examined using differential scanning calorimetry (DSC), and the BPM with the concentration of 1g GG: 0.6 M.wt% of NaClO4 results with low Tg value (42.70 °C) in contrast to other salt-added membranes. From AC impedance analysis, the ionic conductivity calculated for pure GG is 3.87±0.15 ×10−6 S cm−1, and on addition of salt, the membrane 1g GG: 0.6 M.wt% of NaClO4 exhibits enhanced ionic conductivity of 4.85±0.11 ×10−3 S cm−1 at room temperature. Surface morphology analysis and thermal stability of the prepared BPMs have been examined using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Transference number measurement has been done to confirm that the conduction is mainly due to ions. The electrochemical stability for the highest ion conducting membrane has been analyzed using linear sweep voltammetry (LSV). The cycling stability for the prepared biopolymer electrolyte of 1g GG: 0.6 M.wt% of NaClO4 has been obtained using cyclic voltammetry (CV) analysis. The solid-state primary sodium ion battery (SIB) has been constructed using the highest ion conducting membrane and results in an open circuit voltage (OCV) of 2.99 V.