Enhancing EDLC applications with [BMIM]BF₄-integrated cellulose gel electrolyte for sustainable energy storage

Researchers worldwide have extensively carried out the fabrication of supercapacitors using ionic liquid-based gel electrolytes. Gel polymer electrolytes (GPEs) are an excellent alternative electrolyte due to their high ionic conductivity and lack of safety issues associated with solid and liquid polymer electrolytes. This work highlights the performance of a GPE composed of 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM]BF₄ mixed with ammonium nitrate (NH₄NO₃) as the charge carrier, entrapped in methylcellulose (MC) for its application as an electrolyte in supercapacitors. The results of the Fourier transform infrared spectroscopy (FTIR) study are in good agreement with the literature, confirming the interaction between the materials observed through the shifting of the hydroxyl band. Moreover, the addition of [BMIM]BF₄ successfully reduced the degree of crystallinity and crystallite size, thus enhancing the amorphous region of the electrolytes, as observed in the X-ray diffraction (XRD) diffractogram. The sample with 10 wt% [BMIM]BF₄ (IL10) exhibits the highest ambient conductivity of (2.44 ± 0.36) × 10⁻² S cm⁻¹. The obtained ionic transference number (t_ion) of 0.98 confirms that ions are the dominant charge carriers. Considering its electrochemically stability up to 2.6 V within a potential range of 3.0 V, the IL10 electrolyte was chosen as a separator for application in an electric double-layer capacitor (EDLC). The EDLC is characterized via cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) analysis.