Influence of electrolyte ion–solvent interactions on the performances of supercapacitors porous carbon electrodes

• A series of porous carbons with tuneable porous texture were prepared.
• Performance of carbon supercapacitors were evaluated in different electrolytes.
• Relationship between porous texture and solvent–salt interaction was studied.
• Highly polarizing ions in polar solvents do not completely loss the solvation shell.
• The optimal carbon pore size depends on the solvent-ion couple used as electrolyte.

The development of advanced and safe electrochemical supercapacitors or hybrid supercapacitors combining a battery electrode material such as graphite and a porous carbon electrode implies the use of new electrolytes containing a tetra-alkylammonium or lithium salt dissolved preferentially in a safe and environmentally friendly solvent such as alkylcarbonates. In those systems, the carbon porosity of the activated carbon electrode controls the electrochemical behavior of the whole device. In this work, it is demonstrated that electrolytes containing highly polarizing ions such as Li+ dissolved in polar solvents such as alkylcarbonates do not completely loss their solvation shell at the opposite of what is observed for poorly solvated cations like TEABF4. As a consequence, the optimal carbon pore size for obtaining the largest energy density, while keeping a high power density, is wider when strongly solvated cations, like Li+ are used than for conventional organic electrolytes using acetonitrile as solvent and TEA+ as salt cations. TEA+ cations are easily desolvated and hence are able to penetrate in small pores matching the dimensions of bare ions. The dissimilarity of behavior of alkylcarbonates and acetonitrile based electrolytes highlights the importance of ion–solvent interactions when searching the optimal porous texture for the electrode material.