Weakening Coulomb interactions in ionic liquid via hydrogen bonds enables ultrafast supercapacitors.

Abstract

The application of ionic liquid electrolytes in ultrafast supercapacitors to achieve wide electrochemical operating windows and high electrochemical stability is highly applauded. However, the strong Coulomb interaction between ions leads to the overscreening effect and slow establishment process of the electrical double layer (EDL), which deteriorates the rate performance of supercapacitors. Herein, inspired by Coulomb's law and EDL transient dynamics, we introduce competitive hydrogen bond interactions into typical ionic-liquid electrolytes to weaken the Coulomb interaction between ions. Density functional theory calculations, nuclear magnetic resonance spectroscopy, and Fourier infrared spectrum, combined with differential capacitance, suggest that the introduction of competitive hydrogen bonds is responsible for the suppression of Coulomb interaction between ions. The existence of appropriate hydrogen bonds effectively improves the ion coordination and the interface model of the electrode surface, thus enhancing the response kinetics of ions. Based on this hybrid electrolyte design, the fabricated supercapacitor delivers an outstanding capacity of 100.0 mF g^-1 at 120 Hz with a cut-off frequency of 1842.4 Hz and a relaxation time of 0.62 ms. This work opens a pathway towards the design of electrolytes for ultrafast supercapacitors.