Electrochemical Characteristics of Cyclic Structure Additives in EDLCs

Introduction        

Electrochemical double-layer capacitor (EDLC) is on a rise as a kind of Energy storage system (ESS), nowadays.[1] EDLCs work 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.[2] The internal structure of EDLCs are consist 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.[3] So, we need to consider characteristics of solvent and salts. Characteristics of electrolyte are those; electrical stability, ion conductivity, viscosity, high temperature work, cell application.[4] Before papers are almost suggest cyclic structure carbonate as additives in PC, EC or AN-based electrolyte like DEC, DMC, etc. But GBL and PC addition can affirmative affects ion conductivity and potential stability.  

 In this study, we experiment additives for electrolyte in EDLCs. Especially, we focused on the cyclic structure solvents addition. The additive was used Tetrahydrofuran(THF), γ-butyrolactone (GBL) and Propylene Carbonate(PC). Furthermore, we applied electrolyte samples to EDLC cell.

Experiment

First of all, 1M TEABF4 in PC as reference, THF and GBL is added at propylene carbonate 0 to 30% by volume. In this process, whole salt concentration kept as 1M. Each concentration of sample was 5% interval.

Next, we approach PC addition to 1M SBPBF4 in AN. PC addition experiment goes same condition with upper experiment(0~30%, 5% interval).

As Electrochemical properties, Ion Conductivity and LSV were accepted. Ion conductivity determines almost specification of electrolyte. LSV shows electrical stability. Apply to EDLC unit cell, those examine was measured; CV, impedance, charge/dis-charge

 

Result& Discussion

THF and GBL addition shows low viscosity than pristine PC. By using THF and GBL, PC-based electrolyte can decrease viscosity. But THF has not enough electrical stability. In LSV results, yield point was decreased by THF addition. 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. GBL and PC addition gives electrical stability to Cell application shows overall effects at the electrolyte in EDLCs.

References

[1] R. Ko¨tz a, M. Carlen, Electrochimica Acta 45 (2000) 2483–2498

[2] P. Sharma, T.S. Bhatti, Energy Conversion and Management 51 (2010) 2901–2912

[3] S. Takeuchi, K. Miyazaki, F. Sagane, T. Fukutsuka, S.K. Jeong, T. Abe, Electrochimica Acta 56 (2011) 10450– 10453

[4] A. Laheaar, H. Kurig, A. Janes, E. Lust , Electrochimica Acta 54 (2009) 4587–4594