A Flexible Ionic Liquid Gelled PVA-Li2SO4 Polymer Electrolyte for Semi-Solid-State Supercapacitors

A novel high-performance flexible gel polymer electrolyte (FGPE) for supercapacitors is prepared by a freeze-drying method. In the presence of 1-butyl-3-methylimidazolium chloride (BMIMCl) ionic liquid, Li2SO4 can easily be added into poly(vinyl alcohol) (PVA) aqueous solution over a large concentration range. The resultant FGPE demonstrates considerably high ionic conductivity (37 mS cm(-1)) and a high fracture strain at 100% elongation at the optimal weight ratio of PVA:BMIMCl:Li2SO4 = 1:3:2.2. The supercapacitor fabricated with the resultant FGPE and activated carbon electrodes shows an electrode-specific capacitance of 136 F g(-1) with a stable operating voltage of 1.5 V, a maximum energy density of 10.6 Wh kg(-1), and a power density of 3400 W kg(-1). Double supercapacitors in series can efficiently drive a light emitting diode (LED) bulb for over 5 min and the retention of the specific capacitance reaches 90% even after 3000 charge-discharge cycles. The ionic conductivity and charge-discharge behaviors of the resultant FGPE are not affected by bending up to 180 degrees. The flexible supercapacitor device shows only a small capacitance loss of 18% after 1000 cycles of 135 degrees bending.