Simultaneous recycling and nitrogen doping in carbon fiber reinforced plastic using eco-friendly supercritical water treatment for Li-ion batteries anode application

Carbon fiber (CF) is emerging as a high value-added material due to its lightweight nature about 1/4 the weight of steel, coupled with its exceptional strength. In particular, CF reinforced plastic (CFRP), comprising over 60% CF, has gained prominence as a next-generation composite material used in various industries to reduce weight. The widespread use of CFRP has led to a surge in CFRP waste, which arises challenges related to its high cost and waste management, necessitating recycling efforts. However, recycling CFRP is complex because it is composed of thermosetting resins. Conventional recycling methods such as incineration and shredding often result in environmental pollution. Furthermore, during the recycling process, CFs become randomly oriented and primarily repurposed as individual fibers used for reinforcement materials. To address these challenges, our study employs supercritical water for an eco-friendly recycling without the need for catalysts or oxidizers. During this recycling process, we introduced glycine, which simultaneously achieved nitrogen (N) atom doping of the recycled CF. This dual approach resulted in the production of recycled CFs doped with N atoms. These doped and recycled CFs were reused as anode materials for lithium-ion batteries and exhibited a capacity of approximately 340 mAh g−1 (at 0.1C) and a stable cycling lifespan over 150 cycles (at 1C). This promising performance suggests their potential as replacements for traditional graphite anode materials. [Display omitted] •Using supercritical water and glycine, we showed an eco-friendly upcycling method that performs simultaneous nitrogen doping and recycling.•Identify the mechanism of how nitrogen atoms are doped onto the surface of carbon fiber using supercritical water.•Nitrogen-doped recycled fibers are reapplied as anode materials for lithium-ion batteries.•A new direction for overcoming the limitations of recycled carbon fiber through upcycling.