Phosphorus-doped hard carbon derived from waste PET bottles as a superior anode material for lithium-ion batteries

Abstract

Plastic pollution remains a significant environmental challenge, with polyethylene terephthalate (PET) bottles contributing heavily due to their durability and limited degradability. Upcycling PET into functional carbon materials provides a sustainable alternative to conventional recycling routes, which often generate microplastics. Owing to its high carbon content and abundant ester groups, PET serves as an excellent precursor for hard carbon (HC), suitable for use in electrochemical energy-storage applications. In this work, waste PET bottles are upcycled into phosphorus-doped hard carbon (P-HC) through a single-step pyrolysis process using orthophosphoric acid (H₃PO₄). The resulting P-HC demonstrates markedly enhanced electrochemical performance compared with undoped PET-derived carbon. The sample prepared with 3 mL of phosphoric acid exhibits the most favorable properties, delivering a high reversible capacity of 765 mAh g⁻¹ after 100 cycles at 0.2 A g⁻¹ and 531 mAh g⁻¹ after 200 cycles at 2 A g⁻¹. These improvements are attributed to increased interlayer spacing, higher surface area, greater structural disorder, and improved electronic conductivity induced by phosphorus incorporation. The study demonstrates a sustainable route for converting PET waste into high-performance anode materials for lithium-ion batteries (LIBs), addressing both environmental concerns and the growing demand for efficient energy-storage technologies.