Electrochemical Characterization of a Zinc-Based Gel-Polymer Electrolyte and Its Application in Rechargeable Batteries

A gel-polymer electrolyte (GPE) based on a zinc salt is prepared and investigated for possible applications in a rechargeable solid-state zinc battery. The GPE consists of polyacrylonitrile, propylene carbonate, ethylene carbonate, and zinc trifluoromethane sulfonate (zinc triflate, ZnTf). The composition of the GPE is optimized to contain minimum liquid constituents required for the gel formation with maximum specific conductivity $({\sigma} = 2.67\times10^{–3}\hspace{2mm}S\hspace{2mm}cm^{–1}\hspace{2mm}at\hspace{2mm} 27^o{C})$. The specific conductivity $(\sigma)$ variation with temperature follows an Arrhenius behavior with activation energies in the range of 0.12-0.31 eV for different compositions of the gel. Evidence from ac impedance and cyclic voltammetric studies using Zn/GPE/Zn cell indicate reversibility of $Zn/Zn^{2+}$ couple at the electrode-electrolyte interface. Temperature and time-dependent studies have been carried out to probe the interfacial behavior. Equivalent circuit analysis has been carried out to determine the values of interfacial resistance $(R_i)$ of the Zn/GPE that is a combination of the surface film resistance $(R_f)$ on the zinc surface and charge-transfer resistance $(R_{ct})$ of the electrochemical reaction. Cationic transport number measurements yield values of 0.56 at 27°C and 0.14 at 70°C. Several cells have been assembled and the charge-discharge behavior has been followed. Capacities of 98, 65, 47 and 33 mAh $g^{-1}$ of $MnO_2$ have been achieved at current densities of 10, 50, 100, and 200 $\muA/cm^2$ respectively. The charge-discharge studies show a consistent performance for 70 cycles with no significant change in the discharge behavior and capacity values at all current densities studied