Hybrid Deep Eutectic Solvent of LiTFSI-Ethylene Glycol Organic Electrolyte for Activated Carbon-Based Supercapacitors

This research work demonstrates a novel hybrid electrolyte based on a deep eutectic solvent (DES) combined with organic solvents for high-performance supercapacitors. DES was formed between ethylene glycol (EG) and lithium bis((trifluoromethyl)sulfonyl) imide (LiTFSI) and diluted by ethylene carbonate (EC) or acetonitrile (AN) with different amounts (10-50% wt.). Such a combination gives superior properties for hybrid electrolytes compared to pure DESs and reduces the volatility of mixed organic solvents. Regarding the electrochemical properties, DES-AN mixtures exhibited a better performance under high applied voltage and more reversible behavior than DES-EC ones, which suffered from the increasing distance in the electrical double layer. DES 1 : 4 + 20% wt. AN exhibited favorable electrolyte properties such as high ionic conductivity (3.1 mS center dot cm(-1) at 30(o)C), relatively lower viscosity (14.28 mPa s at 30(o)C, approximately 2 times lower thanDES pure), and quite large electrochemical stability window up to 3.4 V (at 20-30% wt. AN) compared to the baseline electrolyte (LiTFSI/TBABF(4) in AN). With these interesting properties, selected hybrid electrolyte (DES 1 : 4 + 20% wt. AN) tested in the symmetric capacitor using the activated carbon offered decent capacitance (15 F center dot g(-1) at 3.4 V with a scanning rate of 1 A center dot g(-1) and remains around 95% after 100 cycles) and good charge-discharge durability (> 80% retention after 2000 cycles), especially the EDLC with DES 1 : 4 + 20% wt. AN shows good rate capacity (13.2 F center dot g(-1) at 2 A center dot g(-1), remaining 6 F center dot g(-1) at 10 A center dot g(-1)).