Upcycling PET Bottles into P-Doped Hard Carbon Anode Materials for Li-Ion Batteries
Authors: Yeskozha Dossym , Nurpeissova Arailym 
Published: December 2024

Introduction

The urgent need to address environmental concerns, particularly the escalating plastic waste crisis, has underscored the importance of exploring innovative methods for enhancing plastic bottle recycling [1]. Among these methods, upcycling—transforming plastic waste into products of greater intrinsic value—has gained significant attention [2, 3].
This study focuses on applying upcycling methods to plastic bottles, with a specific emphasis on Polyethylene terephthalate (PET) materials sourced from the Coca-Cola corporation as a case study. PET bottles are chosen due to their widespread use in consumer markets and their prevalence in plastic waste streams.
The primary objective of this research is to systematically investigate processes for repurposing PET bottles into hard carbon materials. Such materials hold promise for various applications, notably in energy storage systems like lithium-ion batteries (LIBs). By examining PET dissolution in various solvents, this study aims to identify efficient and sustainable pathways for producing high-quality carbon materials.
Additionally, this study integrates phosphorus (P) doping into the synthesis process. P-doping has been demonstrated to enhance the electrochemical performance of carbon materials by altering their electronic and structural properties. The authors successfully synthesized P-doped hard carbon and conducted comprehensive characterization using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. These analyses provide insights into the effects of doping on the structure and morphology of the resulting hard carbon materials, shedding light on mechanisms behind their improved electrochemical performance.
This research aims to contribute to the development of environmentally sustainable solutions for plastic waste management. Through the application of upcycling methods to PET bottles and the integration of P-doping strategies, this study seeks to address the environmental challenges posed by plastic waste while exploring avenues for value-added product creation in advanced technological domains.2.

Experimental

A novel approach is presented for the synthesis of hard carbon material for lithium-ion batteries (LIBs) utilizing recycled PET bottles from Coca-Cola Classic. The bottles underwent thorough washing with water and ethanol, followed by air drying and cutting into small 3-4 mm square pieces prior to dissolution. Solvents for PET dissolution were prepared by mixing dichloromethane (DCM) with trifluoroacetic acid (TFA) in a volume ratio of 3:7. The PET pieces were dissolved in the solvent mixture at a rate of 2 grams per 10 ml of solvent using a stirrer at 100 rpm for 4 hours. P-doping was achieved by adding phosphoric acid (H3PO4) to the plastic solution in various concentrations (1 mol, 2 mol, 3 mol H3PO4 per 10 ml of solution). The resulting solution was applied as a thin layer (50 μm thick) onto a glass surface and dried in air for 24 hours. Subsequently, the resulting film was annealed in an argon atmosphere at 750°C for 2 hours with a heating rate of 5 degrees/min. The resulting carbon materials were characterized and utilized as anodes for lithium-ion half-cells. Electrochemical properties of the batteries were evaluated using cyclic voltammetry (CV) and galvanostatic charge/discharge methods. This study demonstrates a sustainable and efficient method for the synthesis of carbon materials for LIBs from recycled plastic waste, with promising electrochemical performance.

Results and Discussion

The XRD analysis presented in Figure 1 demonstrate that the obtained carbon sample possessed the high-quality attributes required for battery-grade hard carbon which is substantiated by the distinct peaks observed. Moreover, the initial discharge capacity stands at an 758.53 mAh/g, accompanied by an initial Coloumbic efficiency of 49.75%. After the 10th cycle the Coulombic efficiency reached 97.98%. The corresponding capacitance values after the 10th and 50th cycle are 338,35 and 304,71 mA.
Fig. 1 X-ray diffraction pattern of obtained powder

References

Olazabal, I., Goujon, N., Mantione, D., Alvarez-Tirado, M., Jehanno, C., Mecerreyes, D., &#38; Sardon, H. (2022). From plastic waste to new materials for energy storage. <i>Polymer Chemistry</i>, <i>13</i>(29), 4222–4229. https://doi.org/10.1039/d2py00592a

Mirjalili, A., Dong, B., Pena, P., Ozkan, C. S., &#38; Ozkan, M. (2020). Upcycling of polyethylene terephthalate plastic waste to microporous carbon structure for energy storage. <i>Energy Storage</i>, <i>2</i>(6). https://doi.org/10.1002/est2.201

Nagmani, &#38; Puravankara, S. (2023). Utilization of PET derived hard carbon as a battery-type, higher plateau capacity anode for sodium-ion and potassium-ion batteries. <i>Journal of Electroanalytical Chemistry</i>, <i>946</i>. https://doi.org/10.1016/j.jelechem.2023.117731

Figure 1