Valorizing waste PET bottles into Li-ion battery anodes using ionothermal carbonization

Waste poly(ethylene terephthalate) (PET) bottles (WPBs) are fast becoming an environmental nuisance, and their valorization to carbon anodes could be a sustainable method to manage this waste and also develop cheap and high-performance carbon materials for lithium (Li)-ion batteries (LIBs). Carbonaceous materials derived from WPBs were prepared using an ionothermal carbonization (ITC) method in a choline chloride–urea deep eutectic solvent system. The ITC-derived materials were subsequently annealed in air to obtain carbonaceous materials. The ITC-derived carbon displayed ultra-high nitrogen doping but less carbonization and graphitic ordering compared with the equivalent carbon material obtained using hydrothermal carbonization (HTC). Therefore, higher-temperature annealing/pyrolysis was recommended for the ITC-derived carbon. The HTC-derived carbon was investigated as an anode material for an LIB with promising electrochemical performance. The LIB displayed a stable reversible capacity of about 130 mAh/g at a current density of 0.1 A/g after 20 cycles and an increasing coulombic efficiency that reached 98% after the 50th cycle. This work shows that a facile and sustainable synthesis method can be used to produce PET-derived activated carbon with potential applications in energy-storage systems such as LIBs.