**5. Conclusions**

This work demonstrates that aqueous processable biodegradable polymers such as pullulan can be effectively exploited for the development of the major components (separator and binder) of ionic-liquid-based green EDLCs. After studying different combinations of biopolymer and organic electrolyte, pullulan-EmimTFSI was found to be the best system in terms of resistivity and thermal behavior. Therefore, we assembled Pu-based EDLCs with EmimTFSI as electrolyte. Our study demonstrates for the first time the feasibility of the use of pullulan to produce high mass loading electrodes at low binder content for high voltage EDLCs. We prepared electrodes with mass loadings up to 13.84 mg cm−<sup>2</sup> with 10% binder content. Pullulan-EmimTFSI EDLCs were charged up to 3.2 V with good cycling stability over 5000 cycles. Pullulan-EmimTFSI EDLCs featured specific energy and power comparable with those of supercapacitors based on the same activated carbon and ionic liquid, but with fluorinated binder and fiberglass separator.

Further work is in progress to improve the specific capacitance of these thick electrodes by using high surface area carbons with tailored porosity, different conductive carbon additives, and by exploring different electrolytes.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1996-1073/13/12/3115/s1, Figure S1. Schemes of the casting preparation of the pullulan-based electrodes and of the supercapacitor assembly, Figure S2. Nyquist plot of Pullulan electrospun membrane soaked with (a) PYR14TFSI, (c) EmimTFSI, (e) 0.5 m LiTFSI TEGDME and Cellulose triacetate electrospun membrane soaked with (b) PYR14TFSI, (d) EmimTFSI, (f) 0.5 m LiTFSI TEGDME, Figure S3. Trend of the capacitance percentage normalized by the value at first cycle the as function of the cycle number (at 1 A g<sup>−</sup>1, cell voltage cut-off: 0 V–3.2 V), Table S1. Resistance normalized by the plain area of Pullulan electrospun separator in different tested electrolytes, Table S2. Resistance normalized by the plain area of Cellulose triacetate electrospun separator in different tested electrolytes, Table S3. Resistivity of Pullulan electrospun separator in different tested electrolytes, Table S4. Resistivity of Cellulose triacetate electrospun separator in different tested electrolytes, Table S5. Mac Mullin number of Pullulan electrospun separator in different tested electrolytes, Table S6. Mac Mullin number of Cellulose triacetate electrospun separator in different tested electrolytes.

**Author Contributions:** Conceptualization: F.S. Data curation: G.E.S., F.P. Formal analysis: G.E.S., F.P., Funding acquisition: F.S. Investigation: G.E.S., F.P. Project administration: F.S. Supervision: F.S., Writing–original draft: G.E.S., F.P., A.B., D.M., F.S. Writing—review & editing: G.E.S., F.P., A.B., D.M, F.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Italy-South Africa joint Research Programme 2018–2020 (Italian Ministers of Foreign Affairs and of the Environments) and "Piano Triennale di Realizzazione 2019–2021, Accordo di Programma Ministero dello Sviluppo Economico"—ENEA.

**Acknowledgments:** Maria Letizia Focarete (University of Bologna) and her research group are acknowledged for their precious contribution and support on electrospinning of natural polymers.

**Conflicts of Interest:** All The authors declare no conflict of interest for this manuscript.
