Unveiling the Effects of Solvent Polarity within Graphene Based Electric Double-Layer Capacitors

Solvents have been considered to show a profound influence on the charge storage of electric double-layer capacitors (EDLCs). However, the corresponding mechanisms remain elusive and controversial. In this work, the influences of solvent dipole moment on the EDL structures, kinetic properties, and charging mechanisms of graphene-based EDLCs are investigated with atomistic simulations. Specifically, electrolyte structuring is conspicuously modulated by solvents, where a sharp increment of capacitance (~325.6%) and kinetics (~10-fold) is documented upon the slight descent of polarity by ~33.0%. Unusually, such an impressive enhancement is primarily attributed to the suppressed interfacial electric fields stimulated by strong-polarity solvents in the proximity of electrodes, which goes beyond the previously observed issues that stemmed from the competitive interplays between ions and solvents. Moreover, a distinctive polarity-dependent charging mechanism (i.e., from pure counterion adsorption to coion desorption) is identified, which for the first time delineates the pivotal role of solvent polarity in manipulating the charge storage evolutions. The as-obtained findings highlight that exploiting the solvent effects could be a promising avenue to further advance the performances of EDLCs.