Rapid Upcycling of Waste Polyethylene Terephthalate to Energy Storing Disodium Terephthalate Flowers with DFT Calculations

In this work, we report an efficient synthesis approach of disodium terephthalate and its application as a potential battery anode material. Disodium terephthalate is upcycled from waste polyethylene terephthalate flakes with the aid of an ultrafast microwave irradiation process within 2 minutes. The phase and chemical purity of the as-synthesized disodium terephthalate is confirmed by X-ray diffraction, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy. The electrochemical behavior of this low-cost, environmentally benign organic molecular compound is studied in Li- and Na-ion cells. The density functional theory-based calculations are performed to get insights into specifics of electronic properties of Li- and Na-ion cells and rationalize the differences in behavior for the two systems. The delithiation potential of a disodium terephthalate anode is found to be approximately 0.65 V higher than the desodiation potential. The disodium terephthalate-carbon black (Super P) composite electrode delivers discharge capacities of 182 and 224 mAh g–1 at a current density of 25 mA g–1 after 50 cycles in Li-ion and Na-ion cells, respectively. The better C-rate performance of the composite anode for a Li-ion cell, as compared to a Na-ion cell, is due to inferior mobility of Na-ions in the electrode material, which is largely defined by ion size.