Sodium alginate incorporated with magnesium nitrate as a novel solid biopolymer electrolyte for magnesium-ion batteries

Abstract

Solid biopolymer electrolytes have gained much attention in recent years. Due to their various advantages, it can be used in advanced electrochemical devices. The present study focuses on synthesizing and characterizing natural solid biopolymer electrolytes that consist of sodium alginate as the host polymer and magnesium nitrate (Mg(NO₃)₂.6H₂O) as the ionic dopant via solution casting technique. X-ray diffraction analysis of prepared solid biopolymer electrolytes validates the increase in the amorphous nature as salt concentration increases. The interaction and the complexation between the host biopolymer and the magnesium salt are confirmed by Fourier transforms infrared spectroscopy. The solid biopolymer electrolyte composition of 40 M wt.% NaAlg:60 M wt.% Mg(NO₃)₂·6H₂O possesses optimum ionic conductivity value of the order of 4.58 × 10⁻³ S cm⁻¹ as observed by the AC impedance spectroscopy analysis at room temperature. The glass transition temperature (T_g) of the prepared solid biopolymer electrolytes has been studied using differential scanning calorimetry. Linear sweep voltammetry study reveals that the highest magnesium ion-conducting membrane has electrochemical stability of 3.5 V. Further, an optimum ionic conducting solid biopolymer membrane (40 M wt.% NaAlg:60 M wt.% Mg(NO₃)₂·6H₂O) has been utilized to fabricate a primary magnesium ion conducting battery. The open circuit voltage of the proposed solid biopolymer membrane is 1.93 V, and the performance of the battery has been studied.