Abstract
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·cm−1 at 30oC), relatively lower viscosity (14.28 mPa s at 30oC, 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/TBABF4 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·g−1 at 3.4 V with a scanning rate of 1 A·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·g−1 at 2 A·g−1, remaining 6 F·g−1 at 10 A·g−1).
Highlights
Energy shortages and environmental pollution induced by heavy fossil fuel usage have inspired researchers to seek alternative sustainable energy to fossil forms such as wind and solar energy [1]
In the electric double layer capacitor (EDLC) system, electrostatic adsorption of electrolyte ions occurs at the interface between electrode and electrolyte, thereby achieving rapid charge/ discharge cycle, and increases stability though their real potential and energy density which are comparatively lower [6]. e efficiency of supercapacitors is highly affected by the physical and chemical properties of the electrode materials and electrolytes adopted [7]. us, the production of highperformance electrode materials, as well as the stable electrolyte, is the fundamental prerequisite for supercapacitor design. e conventional electrolyte of the supercapacitor consists of organic solvents and alkylammonium salt
To be practically applied in EDLC using activated carbon, hybrid electrolytes based on deep eutectic solvent (DES) mixed with %wt. solvent were investigated. e pure DES at a molar ratio of 1 : 4 between lithium bis((trifluoromethyl)sulfonyl) imide (LiTFSI) and ethylene glycol (EG) was selected to combine with the solvent owing to its lowest viscosity and highest ionic conductivity, as previously reported in our study [23]
Summary
Energy shortages and environmental pollution induced by heavy fossil fuel usage have inspired researchers to seek alternative sustainable energy to fossil forms such as wind and solar energy [1]. E conventional electrolyte of the supercapacitor consists of organic solvents (usually AN) and alkylammonium salt These mixtures have strong conductivity and ion transport properties, they have high volatility, Journal of Chemistry flammability, and toxicity leading to safety and environmental concerns [8]. DESs based on a combination of N-methyl acetamide and LiNO3 demonstrated a low conductivity of around 1.0 mS·cm−1 at 25oC [19], which is significantly lower than the typical value (50 mS·cm−1) for organic electrolytes. E pure DES at a molar ratio of 1 : 4 between lithium bis((trifluoromethyl)sulfonyl) imide (LiTFSI) and ethylene glycol (EG) was selected to combine with the solvent owing to its lowest viscosity and highest ionic conductivity, as previously reported in our study [23] To be practically applied in EDLC using activated carbon, hybrid electrolytes based on DES mixed with %wt. solvent (ethylene carbonate or acetonitrile) were investigated. e pure DES at a molar ratio of 1 : 4 between lithium bis((trifluoromethyl)sulfonyl) imide (LiTFSI) and ethylene glycol (EG) was selected to combine with the solvent owing to its lowest viscosity and highest ionic conductivity, as previously reported in our study [23]
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