Investigations on Na-ion conducting electrolyte based on sodium alginate biopolymer for all-solid-state sodium-ion batteries

Herein, solid biopolymer electrolyte membranes based on sodium alginate are prepared and investigated for their application in sodium-ion batteries. Various concentrations of sodium thiocyanate (NaSCN) are introduced into the matrix of sodium alginate biopolymer. Solution cast route is the method opted to prepare the electrolyte membrane. The complex formation between sodium alginate and NaSCN has been confirmed with the help of X-ray diffraction (XRD) analysis and Fourier transform infrared spectroscopy (FTIR). On increasing NaSCN concentration, the semi-crystalline nature of the sodium alginate gets abated thus elevating the amorphous domain of the electrolyte membrane. Information about the glass transition temperature (Tg) is acquired from differential scanning calorimetry (DSC). Decrement in the Tg upon NaSCN addition favors the segmental motion of the polymer chain. The biopolymer host material (30 wt%) can accommodate large amounts of NaSCN salt (70 wt%) exhibiting ionic conductivity of 1.22 × 10−2 S cm−1. The transference number measurement with Wagner’s DC polarization method is found to be 0.96 (near unity) which confirms ions are the governing charge carriers. The linear sweep voltammetry (LSV) technique that measures the potential window for the biopolymer electrolyte membrane is 2.7 V, representing it as a potential applicant for electrochemical energy storage devices. An all-solid-state sodium-ion battery is assembled with a high ion–conducting biopolymer electrolyte membrane that displays an open cell potential of 2.87 V. The results highlight the possibilities of sodium ion–conducting solid biopolymer electrolytes to extend their hands in a safe sodium-ion battery.