Improvements in the energy density of electric double-layer capacitors (EDLCs) can in particular be gained by enhancing their capacitance. Recent findings suggest that the specific capacitance can be increased by matching the sizes of pores and desolvated ions. However, on such matching, we evidenced that charge storage saturation can occur in tetraalkylammonium solutions before reaching the maximum voltage, e.g., 2.7 V, due to the insufficiently developed porosity. There are strong reasons to believe that the geometry of tetraalkylammonium cations under confinement in nanoporous carbons is highly distorted since the values of maximum electric charge, calculated by adopting such geometry, are in good agreement with the experimentally measured ones. From the point of view of supercapacitor operation, this saturation phenomenon makes it impossible to profit from higher voltage, which limits the energy and power density.
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