*2.1. Materials*

*N*-butyl-*N*-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI, purity >99.9%) was purchased from Solvionic (Toulouse, France). 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EmimTFSI, purity >99%) was purchased from Solvent Innovation (Köln, Germany). Lithium bis(trifluoromethanesulfonyl)imide and tetraethylene glycol dimethyl ether (TEGDME) (purity >99%) were both purchased from Sigma-Aldrich (St. Louis, MO, USA). Activated carbon PICACTIF was purchased from PICA (Basiano, Italy). Conductive carbon additive (SUPER C45) was purchased from TIMCAL (Bodio, Switzerland). Pullulan (P0978, η = 15.0 ÷ 180.0 mPa s, 10% in H2O at 30 ◦C) was purchased from TCI Europe (Zwijndrecht, Belgium). Cellulose triacetate (CTA, Mw = 74,000 g/mol, DS 3.0) was purchased from Honeywell Fluka (Charlotte, NC, USA). Glycerol (purity >99%) was purchased from Sigma-Aldrich. Nickel foam was purchased from Alantum (Munich, Germany).
