Dielectrics and battery studies on flexible nanocomposite gel polymer electrolyte membranes for sodium batteries

Abstract

In the present study, electrochemical impedance analysis in terms of electrical conductivity, dielectric permittivity, and electrical modulus has been carried out of prepared sodium ion-conducting nanocomposite gel polymer electrolyte. To study ion conduction behavior, frequency-dependent AC conductivity has also been analyzed. Dielectric constant (e′) and dielectric loss (e′′) as a function of frequency with different nanofiller SiO2 concentrations as well as at different temperatures ranging from 303 to 333 K have been discussed. The low-frequency region showed high values of dielectric constant due to polarization at the electrode–electrolyte interface. Frequency-dependent real (M′) and imaginary part (M′′) of modulus reveal large capacitance associated with it at lower frequency whereas dispersion (conductivity relaxation) at a higher frequency. The tangent loss (tan δ) of the electrolyte systems has been determined for different frequencies and concentrations of fumed silica nanoparticles. The high conducting nanocomposite gel polymer membrane exhibited an electrochemical stability window of ≈ 3.3 V which is sufficient to apply this material as a separator for electrochemical device application. The conductivity, dielectric, modulus, and electrochemical stability studies reveal that sodium ion-conducting nanocomposite gel polymer electrolytes offer good electrochemical properties and are suitable for application in any electrochemical/power conversion device. The optimized flexible nanocomposite gel polymer electrolyte films have been used in a prototype sodium battery, which shows a stable open-circuit potential of ~ 2.1 V and a significant first specific discharge capacity of ~ 500 mAh g−1 at a drain current of 14 mA g−1.