**2. Materials and Methods**

#### *2.1. Materials*

All synthesized compounds have been characterized through Nuclear Magnetic Resonance (NMR) with a Bruker Avance Ultrashield 400, operating at proton frequency of 400 MHz (Figures S1–S4). The following abbreviations were used for describing NMR multiplicities: s, singlet; d, doublet; t, triplet; q, quartet; hept, heptet; m, multiplet; dd, doublet of doublets; dt, doublet of triplets; td, triplet of doublets; tt, triplet of triplets.

All electrolytes were prepared and handled in a dry atmosphere using Schlenk line and the appropriate Schlenk line glassware. Lithium tetrafluoroborate (LiBF4) was purchased from Merck KGaA (Darmstadt, Germany). All coin cells were assembled in a dry room. The residual water content in the electrolytes was evaluated through Karl–Fischer titration with a Metrohm 831KF Coulometer.

All electrochemical measurements were recorded using a Gamry Instruments Reference 3000™ potentiostat/galvanostat/FRA, controlled via Gamry Instrument Framework™ software. Data analyses were performed using Gamry Echem Analyst™ software.

The EDLCs electrodes used in this investigation are AC-based, coated on Al-foil, and have been provided as a courtesy by Captop s.r.l. The average mass loading of the electrode was 6 mgcm<sup>−</sup>2, and the thickness of the active material was 55 μm.
