Plasticized nano-composite proton-conducting polymer electrolyte based on PVA for energy storage applications:...

Sustainable polymer electrolytes present an attractive option for advancing energy storage devices in alignment with the principles of green chemistry. Solid polymer electrolytes (SPEs) are a promising approach to modern energy storage with an emphasis on the green chemistry aspect, but common host polymers, such as poly(vinyl alcohol) (PVA), usually have limited ionic conductivity and a low dielectric constant. In order to overcome this fundamental constraint, a novel nanocomposite polymer electrolyte (NPE) was successfully synthesized by doping PVA with ammonium triflate (NH₄CF₃SO₃) and plasticizing it with various amounts of the high-dielectric compound glycerol and then adding 3 wt% Al₂O₃ nanoparticles to each plasticized SPE. The synergistic combination was confirmed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR), which indicate a decrease in hydrogen bonding and an increase in structural disorder. The FTIR spectra established a fundamental improvement in salt dissociation and ion mobility. The XRD pattern of the NPE compared with that of the SPEs confirmed the expansion of more amorphous regions. This disruption reduces the structural ordering index to 16.1%, expanding the amorphous phase, which is highly favorable for enhanced ion transport. Consequently, the NPE delivered an outstanding room-temperature DC ionic conductivity of 1.01 × 10^-3 S cm^-1 and a high ionic transference number of 0.913, while the dielectric evaluations showed a nearly constant dielectric value that is double the value of the dielectric loss over the frequencies tested. Linear sweep voltammetry showed good electrochemical stability, with a window of up to 2.1 V. The symmetric electric double-layer capacitor (EDLC) based on activated carbon electrodes established a rectangular format of CV curves, which indicated charge storage at the electrode/electrolyte interface. The EDLC device under charge-discharge configuration delivered a linear discharge curve, and the system provided an extremely high specific capacitance of ∼200 F g^-1. This device achieved an energy density of 27.37 W h kg^-1, a maximum power density of 2322.16 W kg^-1, and excellent reversibility, with a coulombic efficiency of 97-99% after 350 cycles. Finally, these structural and electrical improvements give rise to an EDLC with extremely competitive energy storage properties, featuring energy densities of supercapacitors and approaching those of conventional batteries.