Enhancement Ion Conductivity with Additives Electrolyte for Electric Double Layer Capacitors
Electrochemical double-layer capacitor (EDLC) is on a rise as a kind of Energy storage system (ESS), nowadays. EDLC works by physical charge and discharge electrons at double-layer (also known as Helmholtz layer). Therefore, EDLCs have high power density and long cycle life, but energy density is very low. The internal structure of EDLC is consists of cathodic/anodic electrode, electrolyte and separator for prevention of short. Among of them, electrolyte is influence at internal resistance of EDLCs. Because of electrolytes were composed solvent and electrolytic salts. So we need to consider characteristics of solvent and salts. Characteristics of electrolyte are those; potential stability, ion conductivity, viscosity, high temperature work, cell application.
In this paper, we experiment additives in PC-based electrolyte. The additive was used γ-butyrolactone(GBL). Before papers are almost suggest cyclic structure carbonate as additives in PC or EC-based electrolyte like DEC, DMC, etc. But GBL also shows lower viscosity and wide temperature range. Furthermore, GBL has good oxidation stability. Those properties of GBL lead to good additive material in PC-based electrolyte.
1M TEABF4 in PC as reference, GBL is added at propylene carbonate 0 to 10% by volume. In this process, whole salt concentration kept as 1M. Each concentration of sample was 1% interval.
Physical properties are measured by viscometer and DSC. Electrochemical properties are Electrochemical Impedance Spectroscope(EIS) and Linear Sweep Voltammetry(LSV). EIS shows resistance of electrolyte samples. Resistance and ion conductivity has inverse relationship. So, we can explain ion conductivity by EIS data. LSV shows electrical stability. Apply half cell and full cell, CV, impedance, charge/dis-charge was measured, too.
Result & Discussion
In viscosity result shows that the 10% GBL sample has most low value. By using GBL, PC-based electrolyte can decrease viscosity. Theoretically, boiling point of GBL is 206°C and flash point is over 80°C. So, GBL addition is enlarge non-flammable properties. Ion conductivity was observed by impedance. To suggest colligate property, the temperature range set 20°C to 80°C, and the interval is 10°C. By measuring LSV, current plateau area was detected that the area is stable potential range.
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