Abstract
A novel nanofibrous gel electrolyte was prepared via gelatin electrospinning for use as a nonaqueous electrolyte in electric double-layer capacitors (EDLCs). An electrospinning technique with a 25 wt% gelatin solution was applied to produce gelatin electrospun (GES) nanofiber electrolytes. Structural analysis of the GES products showed a clearly nanofibrous structure with fiber diameters in the 306.2–428.4 nm range and exhibiting high thermal stability, high tensile strength, and a stable form of nanofibrous structure after immersion in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4). After testing over a range of spinning times, GES electrolytes that were produced at 25 min (GES-25) had a suitable thickness for the assembly of EDLC with the optimized tensile properties and were used to fabricate EDLC test cells with EMImBF4. These test cells were compared to those with pure EMImBF4 and a separator as an electrolyte. The electrochemical properties of the test cells were characterized by charge-discharge testing, discharge capacitance, and alternative current (AC) impedance measurements. AC impedance measurements showed that the test cell with the GES-25/EMImBF4 gel electrolyte showed slightly poorer contact with the electrode when compared to that with pure EMImBF4, whereas exhibited comparable IR drop and discharge capacitance (calculated capacitance retention was 56.6%). The results demonstrated that this novel gel electrolyte can be used as a nonaqueous electrolyte in order to improve the safety in EDLCs.
Highlights
IntroductionElectric double-layer capacitors (EDLCs) represent a class of energy storage devices that can store electrical energy converted from sustainable sources. ey are distinguished from other energy storage devices owing to their several unique characteristics such as higher power density with a longer charge-discharge cycle (
All samples showed similar absorption peaks. e characteristic peaks were interpreted as follows: the peak around 3300 cm−1 is due to the stretching vibration of N–H and hydrogen bonding. e peak at 1650 cm−1 corresponds to the stretching vibration of C O. e peak at 1540 cm−1 is induced by the bending and stretching vibration of N–H, and the peak at 1240 cm−1 is attributed to the bending of N–H. ese absorption peaks are characteristic of gelatin [39, 55]; the presence of these peaks proves that the electrospinning process did not alter the functional groups of the gelatin
The gelatin electrospun (GES)-25/EMImBF4 sample showed two distinctive thermal degradation stages. e first stage was observed at a temperature similar to that of gelatin powder and all GES products due to the degradation of the protein. e second stage was observed at 423°C due to the decomposition of EMImBF4 [62]; this can be seen in the TG and DTG results for pure EMImBF4. ese results demonstrate a high thermal stability and imply that GES fibers may potentially be used as gel electrolytes in Electric double-layer capacitors (EDLCs) under high-temperature operations
Summary
Electric double-layer capacitors (EDLCs) represent a class of energy storage devices that can store electrical energy converted from sustainable sources. ey are distinguished from other energy storage devices owing to their several unique characteristics such as higher power density with a longer charge-discharge cycle (
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