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

The study reports solid-state ceramic supercapacitors (SSCs) assembled using a novel composite electrolyte based on Li⁺ ion conducting perovskite-type LLTO (Li_0.34La_0.51TiO₃) 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 10 000 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.