image: A grave-to-cradle strategy for co-upcycling spent LiFePO4 batteries and PET plastics into high-value BHET monomers via photothermal catalysis.
Credit: ©Science China Press
Building Catalysts from Spent Batteries
At the heart of this strategy is a catalyst made by engineering materials extracted from retired LFP batteries. The research team first separated FePO4 cathodes and graphite anodes from the used cells. The graphite underwent chemical treatment to remove lithium ions and serve as a light-absorbing carrier. The iron was extracted from FePO4 in solution form and then deposited onto the recycled graphite through a controlled impregnation and pyrolysis process.
The resulting FeOX/graphite hybrid combines the broadband light absorption properties of carbon with the catalytic power of iron oxide. High-resolution electron microscopy revealed a uniform dispersion of Fe2O3 nanoparticles across the graphite surface, ensuring efficient light-to-heat conversion and catalysis.
This photothermal catalyst was specifically designed to harness solar energy and generate localized heat, which plays a central role in breaking down polyester chains into valuable monomers. “This is not just a recycling process; it’s an upcycling strategy that turns low-value waste into high-value functional materials,” said Prof. Jinxing Chen, co-corresponding author of the study.
Solar-Powered Depolymerization of PET
To test the real-world applicability of their catalyst, the team conducted experiments using PET plastic—a dominant polyester in global use—under simulated sunlight (0.73 W cm−2). Within 1 hour, PET conversion reached nearly 59%, and monomer (BHET) yield surpassed 39%. These figures represent over threefold and eightfold improvements, respectively, compared to conventional thermal processes operating at the same temperature.
Kinetic analysis confirmed that the enhanced performance stems from localized heating rather than any photochemical effect. Both thermal and photothermal processes followed the same reaction pathway, but the solar-driven system achieved superior efficiency at a lower energy cost.
In extended use tests, the catalyst maintained over 90% of its original efficiency across 15 cycles, underscoring its robustness. “This kind of durability is essential for practical application,” said Prof. Guiling Wang, co-corresponding author from Harbin Engineering University. “We wanted to ensure that the system wouldn’t degrade after repeated use, and it didn’t.”
Proven Viability in Outdoor Solar Conditions
Going beyond lab-scale validation, the team designed an outdoor photothermal reactor powered by natural sunlight and equipped with a Fresnel lens to concentrate solar rays. Under field conditions, the system heated the reaction medium to over 190 °C and achieved 99.8% PET conversion within 30 minutes. It yielded 39 grams of high-purity monomers from the test sample—a recovery rate of over 94%.
The system was also tested with real-world post-consumer PET waste, including colored bottles, packaging films, textiles, and plastic lunch boxes, many of which contain pigments, fillers, or mixed polymers. Even under these conditions, the catalyst showed excellent activity and selectivity, demonstrating its potential to process heterogeneous waste streams.
From Concept to Commercial Viability
To evaluate economic feasibility, the researchers performed a full techno-economic analysis (TEA) using Aspen Plus software. Their model assumed an industrial-scale plant processing 100,000 tons of PET annually. With a minimum selling price (MSP) of $1.003 kg−1 for the recovered BHET—12% lower than the average price of virgin monomers—the process proved financially viable.
Furthermore, the energy consumption for photothermal glycolysis was significantly lower than that of conventional thermal routes, leading to a reduction of 34,474 tons of CO2-equivalent greenhouse gas emissions per year. The process also decreased other air pollutants like acidic gases by over 83 tons.
“The economic advantage here is not just in the lower product cost,” Prof. Chen emphasized. “By integrating solar energy and waste-to-resource principles, we also cut emissions and environmental impact, which are increasingly important for policy and industry.”
A Platform for Circular Innovation
The implications of this dual-waste strategy extend beyond just one type of plastic or battery chemistry. The modular design of the catalyst synthesis process allows it to adapt to different battery materials and plastic types, suggesting wide applicability across the recycling industry.
“This is more than a scientific advance—it’s a new framework for how we can think about materials at the end of their life,” said Prof. Wang. “Rather than dismantling everything down to the elemental level, we selectively transform waste into something functionally superior.”
The team proposes several pathways to scale up and further improve the technology: increasing plant capacity, implementing waste heat recovery systems, and optimizing raw material sourcing. Future studies will explore simplified one-pot processes for catalyst fabrication and analyze batteries with various aging conditions to refine performance predictability.
About the Study
The study, entitled Repurposing Spent LiFePO4 Batteries for Sustainable Photothermal-Upcycling of Polyesters, was published in Science China Chemistry. It was led by researchers from the State Key Laboratory of Bioinspired Interfacial Materials Science, Soochow University; the College of Materials Science and Chemical Engineering, Harbin Engineering University; and the Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences.
This work was supported by the National Natural Science Foundation of China, Jiangsu Provincial Fund for Excellent Young Scholars, and other regional innovation and talent programs.