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.