Solid-state rechargeable magnesium cell with poly(vinylidenefluoride)–magnesium triflate gel polymer electrolyte

A gel polymer electrolyte (GPE) film of poly(vinylidenefluoride) and magnesium triflate is prepared and studied for application in a solid-state rechargeable magnesium battery. The composition of GPE is optimized in view of minimum liquid components and maximum specific conductivity (\sigma). The \sigma of GPE of optimum composition is $2.67\times10^{- 3}S \hspace{2mm} cm^{-1}$ at 20°C, and it follows a Vogel, Tamman and Fulcher equation with an activation energy of about $0.4 \hspace{2mm}kJ mol^{- 1}$. The effect of aging on the Mg/GPE interface is studied. The formation of a passivating film on the Mg surface, which increases in thickness on aging in GPE, is established. Several $Mg/GPE/MnO_2$ cells are assembled and studied for discharge capacity and cyclic-life data. The results reveal that $Mg/GPE/MnO_2$ cells at C/8, C/6 and C/4 discharge rates yield, respectively, capacities of 160, 80 and 50 $mAh \hspace{2mm}g^ {- 1}$ of $MnO_2$. These values are nearly constant for about 30 cycles. Further cycling of the cells leads to a decrease in capacity, which is attributed to passivation of the magnesium electrode and poor efficiency of the $Mg^{2 +}$ ion insertion into the $MnO_2$ positive electrode