Tricationic
ionic liquid (TIL) electrolytes have been successfully
employed in supercapacitors with graphene electrodes, but the low
power density of the TILs-based supercapacitors caused by strong cations–anions
associations requires enhancement by adding organic solvents to the
liquid. In this paper, the role of the solvents acetonitrile (ACN)
and ethylene carbonate (EC) on the ion diffusion, the conductivity
of the TIL [C6(mim)3](Tf2N)3, and the structures and the capacitances of the electrical double
layers (EDLs) in TIL/ACN and TIL/EC electrolytes were probed by molecular
dynamics (MD) simulations. The results indicate that adding organic
solvents to the liquid significantly reduces interactions between
ions, thereby greatly improving the ion diffusion coefficients and
the conductivity of the TIL, and the maximum conductivity is found
at the 0.55 M TIL/ACN electrolyte concentration. Moreover, the reduced
packing of counterions and the strong expulsion of coions near charged
electrodes are observed in the organic electrolytes, especially in
the TIL/EC electrolyte. Further analyses on EDLs affirm that the asymmetric
camel-shaped differential capacitance–voltage (C–V) curve in the pure TIL electrolyte is
weakly changed by the solvent ACN or EC. Besides, the EDL capacitance
in the TIL-based hybrid electrolytes is improved slightly by the organic
solvents. Comparing the integral capacitances in TIL/ACN and TIL/EC
with different solvent contents, it is found that reducing the solvent
polarity may be more beneficial to promote the EDL capacitance. Comprehensively,
in this work, the 0.55 M TIL/ACN electrolyte is the optimal choice
for the high-performance supercapacitor. Hence, solvating TIL electrolytes
in supercapacitors by suitable solvents can effectively enhance the
power density without compromising energy density.