Unraveling lithium-ion intercalation in lead-free bismuth-based vacancy ordered halide perovskites supercapacitors

Abstract

Halide perovskites have recently gained a lot of attention in energy storage applications because of their unique properties. The difficulty in getting high-performance supercapacitors requires the significant development and customization of electrode materials. This study explores vacancy-ordered lead-free halide perovskites with chemical formula A3B2X9 as electrode material for supercapacitors. Furthermore, we have tuned the X site (X = Br−, Cl−, I−) to see the effect of halide ions on supercapacitor performance. Due to high ionic mobility and BET surface area, Cs3Bi2I9 has a specific capacitance of ∼242 F/g and energy density of ∼140 Wh/kg; however, power density variation is almost the same for all samples, measured in three-electrode systems. We have performed the ex-situ XRD and FTIR to understand the structural changes before and after charging. XPS measurement shows the peak shifting before and after measurement in Lithium-based electrolytes. Further, we have fabricated double perovskite-based symmetric devices with gel electrolyte as a separator. The Cs3Bi2I9 device shows an areal energy density of ∼23 μWh/cm2, the highest among all halide perovskite-based supercapacitor devices reported to date. The flexible device on the S.S. substrate shows 79% and 82% capacitance retention up to 180° bending angle and 200 bending cycles, respectively.