Construction of Cellulose Polyvinyl Alcohol Ionic Gels and Application of Flexible Supercapacitors

Abstract

Taking natural cellulose, polyvinyl alcohol (PVA), and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF₄) as raw materials, a flexible energy storage material with both environmental friendliness and superior electrochemical performance was successfully prepared via a solvent replacement regeneration technique. This cellulose/polyvinyl alcohol composite ionic gel electrolyte, designated as Cel/PVA-BF₄ gel, exhibited a three-dimensional porous network structure as observed by scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FT-IR) confirmed the reconstruction of intermolecular hydrogen bonds, while X-ray diffraction (XRD) patterns indicated a significant decrease in crystallinity. Thermogravimetric (TG) analysis verified that the material remained stable over a wide temperature range from -18°C to 120°C. The introduction of [Emim]BF₄ enabled the Cel/PVA-BF₄ gel electrolyte to achieve an ionic conductivity of 18.2 mS/cm. An integrated flexible supercapacitor was successfully constructed using the Cel/PVA-BF₄ gel. This capacitor exhibited three breakthrough advantages: a high voltage window of 3.5 V, surpassing the limitations of traditional aqueous systems; an energy density of 24 Wh/kg, reaching the level of commercial lithium thin-film batteries; and demonstrating remarkable cycling stability, maintaining over 94% of its capacity after 5,000 charge-discharge cycles, which is superior to most reported values in the literature.