Natural Cellulose: A Green Alternative Binder for High Voltage Electrochemical Double Layer Capacitors Containing Ionic Liquid-Based Electrolytes

Natural cellulose has recently emerged as potential candidate for replacing fluorinated polymers (e.g. PVdF) binders in electrochemical double layer capacitors (EDLC) and lithium-ion batteries. In the present work it is demonstrated that, among the advantages offered by its natural origin, cellulose fibers enables superior performance retention under float test at high voltage compared ot PVdF. Specifically, the performance of cellulose-based EDLCs with neat N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR 14 TFSI) electrolyte are investigated upon prolonged float voltage tests at 3.7 V. After 750 hours, cellulose-based EDLC soffered capacitance retention of 52.7% with respect to only 7.5% provided by the PVdF-based ones. For both kinds of devices, post-mortem analysis carried out on the electrolytes suggests a partial decomposition of the electrolyte, leading, at some extent, to the passivation/clogging of the electrode. Nevertheless, the main aging mechanisms seem to concern the electrodes' mechanical and chemical stability. PVdF binder rapidly degrades, thus causing dramatic capacitance losses, especially at the negative electrode. On the contrary, cellulose does not show any particular evidence of failures and the electrode morphology after 750 hours float voltage resembles that of the pristine electrode.