Redox‐Enhanced Ionogels for Stretchable High‐Energy Density Electrochemical Capacitors

Abstract Developing stretchable energy storage devices with high energy and power densities poses a significant challenge for future wearable/deformable electronics. This study proposes new redox (R)‐ionogels that incorporate organodisulfides as redox species for high‐energy, stretchable redox‐enhanced solid‐state electrochemical capacitors (R‐SECs). The R‐SECs are prepared using R‐ionogels made from tetraethylthiuram disulfide (TETDS), 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]), and a physically crosslinked polymer network (poly(vinylidene fluoride‐co‐hexafluoropropylene), P(VDF‐HFP)), sandwiched between two carbonaceous electrodes. Cyclic voltammetry and galvanostatic charge/discharge characteristics of the R‐SECs demonstrated both effective redox reactions and non‐faradaic capacitive energy storage. The optimized 0.25 M TETDS R‐ionogel achieved a specific capacitance of 405 F g ‒1 , 83% rate retention, 80% cyclic stability after 2000 cycles, an energy density of 117 Wh kg ‒1 , and a power density of 5.9 kW kg ‒1 . Additionally, the 0.25 M TETDS enhanced the mechanical properties of the ionogel, increasing the strain at break from 1.92 to 3.25 and toughness from 0.38 to 1.35 MJ m⁻ 3 . Finally, stretchable R‐SECs possessing excellent stretching/releasing durability at 100% strain and volumetric energy densities 26.3 mWh cm −3 that surpass the upper bound of the Ragone plot for reported stretchable capacitors are successfully fabricated for the first time.