High energy density solid state symmetric supercapacitors using ionic liquid dispersed Li+ ion-perovskites

Abstract

The study reports solid-state ceramic supercapacitors (SSCs) assembled using a novel composite electrolyte based on Li+ ion conducting perovskite-type LLTO (Li0.34La0.51TiO3) and an ionic liquid (EMIM BF4). Small amounts of various ionic liquids (ILs) were added to LLTO to enhance the ionic conductivity and improve electrode compatibility. The optimal composition with approximately ∼6 wt% EMIM BF4 in LLTO exhibited a high ionic conductivity of around ∼10−3 Ω−1 cm−1 at room temperature, nearly three orders of magnitude higher than that of the pristine LLTO. Optimized electrolyte composition was therefore used for fabrication by compressing between high surface area activated carbon-coated copper electrodes and assembled in an affordable lamination cell geometry. The SSCs demonstrated stable cycling performance for at least 10[thin space (1/6-em)]000 cycles at 2 V operating voltage and 1.13 A g−1 (2 mA) discharge current, with a remarkably high coulombic efficiency of ∼99%. A typical laminated cell at 35 °C exhibited a specific capacitance of around 510 F g−1 at 0.57 A g−1 (1 mA), and 2 V. Supercapacitors operating below 2 V showed a pure electric double-layer type nature. A stack of 4 cells in series can power two white LEDs (6 V) for ∼40 minutes.