Performance study of sodium alginate (SA) with lithium chloride (LiCl)-based solid-state membrane as an electrolyte in electrochemical device application

In this article, we present a novel solid biopolymer-based membrane (BPM) with sodium alginate (SA) as host material incorporated with an ionic salt, lithium chloride (LiCl). Solid BPMs are prepared using the solution casting technique and used as an electrolyte in the fabrication of solid-state Li-ion conducting battery and coin cell. The X-ray diffraction (XRD) method has been carried out to analyze the crystalline/amorphous nature of the membrane. A Fourier transform infrared spectroscopy (FTIR) study is done to confirm the complex formation between the host biopolymer and salt. The ionic conductivity of all prepared BPMs is measured using AC impedance analysis, and the membrane with the composition of 15 mol% of SA:85 mol% of LiCl exhibits a high ionic conductivity of 3.06 x 10-2 S/cm. The glass transition temperature (Tg) of the prepared BPMs is examined using differential scanning calorimetry (DSC), and the membrane of 15 mol% of SA:85 mol% of LiCl exhibits a decreased Tg value of 54.33 degrees C. The thermal stability of the prepared membranes is studied using thermogravimetric analysis (TGA). Transference number measurement (TNM) is made to assure that the major charge carriers involved in transportation are ions. Using the highest ion conducting membrane as an electrolyte, a primary Li-ion conducting battery has been fabricated which results in an OCV of 1.91 V, and various loads are connected to observe the corresponding current drawn from the cell. A coin cell is constructed with the configuration of graphite (G) + tannic acid || 15 mol% of SA:85 mol% of LiCl || LiFePO4 + G + pinch of highest ion conducting membrane, and the galvanostatic charge-discharge (GCD) analysis is carried out to analyze the rechargeable nature of the prepared membrane and the performance of the coin cell, whereas the cell has undergone charge/discharge process for 200 cycles and resulted with an energy density of 13.94 Wh/Kg, power density of 1111.11 W/Kg, and specific capacitance of 100.40 F/g, respectively.