High-performance Mg-ion conducting poly(vinyl alcohol) membranes: Preparation, characterization and application in supercapacitors

The highly stretchable pure poly(vinyl alcohol) (PVA) membranes with high amorphicity and large ductility are prepared based on an N-methylpyrrolidone (NMP) solution. Meanwhile, the PVA based gel electrolyte membranes doped with magnesium trifluoromethanesulfonate (Mg(Tf)2) and plasticized with 1-ethyl-3-methylimidazoliumtrifluoromethanesulfonate (EMITf) are fabricated with the NMP as the solvent. For the plasticized membranes, the 60PVA-40Mg(Tf)2 + 10EMITf electrolyte system exhibits the highest room-temperature ionic conductivity (1.2 ×10−3 S cm−1), excellent thermal performance and satisfying strength and flexibility. This system is applied for the fabrication of electric double-layer capacitors (EDLCs), acting as both separator and electrolyte. The EDLC shows a specific capacitance of 118 F g−1 with an excellent stability and almost 100% coulombic efficiency over 1000 charge-discharge cycles when charging at 0.85 V under a current density of 313 mA g−1. When the charging voltage is increased to 2 V, the stability of the EDLC somewhat decreases but the coulombic efficiency is still near 100%. Additionally, the CV curves exhibit symmetrical and ideal rectangular shapes without the presence of redox peaks at low scan rates even for 1000 cycles. Consequently, this polymer electrolyte system should be an excellent candidate for ion device applications.