Evaluation of a 1-Butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid-Based Electrolyte and Its Performance in an Electrochemical Double-Layer Capacitor

An ionic liquid (IL)-based polymer electrolyte (PE) was prepared with the polymer polyvinylidene fluoride-co-hexafluoropropylene (PVdF-co-HFP), using 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (1B3MITFSI) and zinc trifluaromethenesulfonate (Zn(CF3SO3)(2)-ZnTf) as the IL and the salt, respectively. The composition 23.6% PVdF-co-HFP: 52.9% ZnTf: 23.6% 1B3MITFSI showed the highest room temperature ionic conductivity of 9.9x10(-3) S cm(-1) with good mechanical properties. The electrolyte was purely an ionic conductor with dominant contribution from cations. The electrochemical stability window of the electrolyte was found to be from 0.1 V to 2.25 V. An electrochemical double-layer capacitor (EDLC) with the configuration polyvinylidene fluoride (PVdF):natural graphite (NG)/1B3MITFSI-based PE/PVdF:NG was fabricated successfully. Impedance results showed that the single electrode specific capacitance (C-sc) of the EDLC was 4.5 F g(-1) and the relaxation time constant was 10.7 s. Continuous cyclic voltammetry was done within the potential window of 0.1 V to 2.0 V at a scan rate of 10 mV s(-1). The initial C-sc was 26.5 F g(-1) and its retention was above 65.5% over 500 cycles. The single electrode-specific discharge capacitance (C-sd) at the first cycle was found to be 5.0 F g(-1) through galvanostatic charge discharge test. It remained steady at 4.0 F g(-1) over 10,000 charge-discharge cycles. Results confirm that the EDLC has a good stability and its degradation is quite low with the efficiency above 70%. This further proves the viability of the system as a promising energy storage device.

Automated summary

An ionic liquid-based polymer electrolyte with high room temperature ionic conductivity and good mechanical properties was prepared using PVdF-co-HFP as the polymer, 1B3MITFSI as the IL, and ZnTf as the salt. The resulting electrolyte showed promising potential for applications in energy storage devices such as batteries.