Highly efficient gel polymer electrolytes for all solid-state electrochemical charge storage devices

Gel polymer electrolytes are prepared using poly(vinylidene fluoride-co-hexafluoropropylene) polymer matrix and 1- propyl-3-methyleimidazolium bis(trifluromethylesulfonyl)-imide ionic liquid and also by adding lithium bis(trifluoromethanesulfonyl)imide salt and plasticizer mixture (ethylene carbonate: propylene carbonate in the ratio 1:1). Thermal and electrical properties of these electrolytes are first investigated. The electrical conductivity of these electrolytes is analyzed over a wide frequency range using a universal power law coupled with modified Poisson-Nernst-Planck model for electrode polarization. All electrolytes show excellent thermal stability up to 340 °C, high ionic conductivity (∼1 × 10⁻³ S cm⁻¹) and wide potential window (∼4.0 V). Supercapacitors are fabricated with these electrolytes using activated carbon as electrodes and their electrochemical properties are studied. The cyclic voltammetry curves show almost box-like shape corresponding to an ideal and reversible capacitive characteristic. The specific capacitance of supercapacitors increases with the addition of lithium salt and plasticizer mixture. The cycle stability of these supercapacitors up to 4000 cycles confirms their electrochemical stability. A lithium ion coin cell is also fabricated using electrolytes containing plasticizer mixture. At ambient temperature, the fabricated cell delivers high specific discharge capacity (∼165.8 mAh g⁻¹) for the first discharge cycle at a constant current rate C/12.