Abstract
The effect of introducing silicon nitride (Si3N4) nanoparticles on the structure and electrochemical properties of fibrous membranes derived from recycled polyethylene terephthalate (PET) cups, obtained by electrospinning, was investigated. Three compositions were prepared: pure PET and PET containing 1 and 2 wt.% Si3N4. The morphology, chemical composition, and distribution of the inorganic phase were characterized by FTIR spectroscopy, scanning electron microscopy, and energy-dispersive X-ray analysis. It was found that the addition of Si3N4 increases the membrane thickness from ~25 μm (PET) to ~91 μm (1 wt.%) and ~127 μm (2 wt.%), with a predominantly uniform distribution of nanoparticles and only isolated aggregates observed in both composite samples. Electrochemical properties were evaluated by impedance spectroscopy and galvanostatic testing in half-cells with a LiFePO4 cathode. The sample containing 1 wt.% Si3N4 was shown to exhibit the highest ionic conductivity and discharge capacity of 163 mA·h/g. At 2 wt.%, the ionic conductivity remains higher than that of pure PET, whereas the discharge capacity decreases to 126 mA·h/g, which may indicate the occurrence of side reactions. The results demonstrate the promise of modifying secondary PET with 1 wt.% Si3N4 for the fabrication of separators.