Aligning TiO2 nanofiber for high ionic conductivity in cellulose acetate gel electrolytes

Abstract

The escalating need for sustainable energy storage systems has prompted enhanced investigations into the advancement of environmentally acceptable, flame-retardant, and high-performing polymer gel electrolytes. The present study examines the ionic conductivity and electrochemical characteristics of gel polymer electrolytes (GPEs) based on cellulose acetate (CA) incorporated with disordered and electric-field-induced aligned TiO2 nanofibers. The results of our study indicate that the arrangement of nanofibers within the CA matrix significantly affects the electrical properties of these electrolytes. The highest ionic conductivity of GPEs containing randomly distributed nanofibers is 5.48 × 10−4 S/cm when the nanofiber content is 2.5 wt%. On the other hand, 2.5 wt% aligned nanofibers containing GPE shows a slightly higher room temperature ionic conductivity of 6.2 × 10−4 S/cm. Nevertheless, the alignment of these nanofibers strategically leads to a gradual enhancement in ionic conductivity, ultimately reaching its maximum value of 5.99 × 10−3 S/cm at a concentration of 10 wt% at room temperature. Significantly, the level of conductivity exhibited in this case is more than 1.5 orders higher than the conductivity observed in disordered nanofiber dispersion within the CA matrix. The improved performance can be due to the creation of long-distance conduction channels enabled by the alignment of nanofibers. The incorporation of well-aligned nanofibers into GPEs results in a high Li+ ion transference number of 0.71, an excellent electrochemical stability window of 4.9 V, and exceptional interfacial compatibility with metal electrodes. In addition, the polymer electrolytes exhibit improved flame-retardant properties when 10 wt% aligned nanofibers are added, enabling the samples to endure exposure to a flame for a period of 10 s. These results indicate the potential suitability of the nanocomposite gel polymer electrolytes (NCGPEs) for application in future advanced energy-storing systems. XRD, FTIR, and XPS investigations further confirm the ion-conduction features of the produced NCGPEs. The investigation of increased electrical characteristics of NCGPEs was supported by a detailed computer simulation conducted using density functional theory (DFT).