Solid-state Mg/MnO2 cell employing a gel polymer electrolyte of magnesium triflate

In view of the abundant resources, low costs and the relatively low reactivity of magnesium, solid-state batteries using this metal are worthy of investigation in comparison with solid-state lithium batteries. For such cells, a gel polymer electrolyte (GPE) is prepared using polyacrylonitrile, propylene carbonate, ethylene carbonate and magnesium triflate. The composition of GPE is optimized in view of the minimum liquid components required for gel formation and maximum ionic conductivity. This is achieved by preparing several films with varying concentration of the constituents and measuring their ionic conductivity by AC impedance spectroscopy. Mg/GPE/MnO2 cells are assembled and their discharge behaviour is studied. A capacity value of about 40 mA h per gram of MnO2 is obtained. Cyclic voltammetric experiments demonstrate qualitatively the reversible behaviour of the MnO2 electrode. The Mg/GPE/MnO2 cells are subjected to about 20 charge–discharge cycles with a consistent capacity of about 20 mA h g−1. Cycle-life data is limited by surface passivation of the magnesium negative electrode and poor rechargeability of the MnO2 positive electrode. At present, the results show that the Mg/GPE/MnO2 cells have an inferior performance in comparison with that of well-developed, lithium-based rechargeable batteries. Further extensive investigations are required to raise the performance of the magnesium-based rechargeable cells to practical levels.