Enhancing crystallinity of recycled carbon fibers by synergistic role of alkaline salts and CaCO3 for lithium-ion batteries

Carbon fibers (CFs) have been developed for use in various fields including sport, aerospace, and electrochemical storages, due to its multifunctional properties such as high mechanical strength, electrical conductivity, and lightweight nature. However, their intrinsically disordered, non-graphitizable structure limits their application as anode materials in lithium-ion batteries (LIBs). In this study, we introduce a catalyst-assisted thermal treatment strategy to enhance the crystallinity and electrochemical performance of recycled CFs (rCFs). A binary mixture of calcium carbonate (CaCO 3 ) and potassium hydroxide (KOH) was applied to the rCF surface prior to one-step carbonization at 1600 °C. KOH effectively removes amorphous carbon, while CaCO 3 promotes the growth of graphitic domains. The synergistic effect led to significantly improved structural ordering. The rCF treated with the CaCO 3 and KOH mixture (CaCF-KOH) exhibited a significant increase in capacity to 284 mAh g -1 , compared to untreated rCF (175 mAh g -1 ) and rCF treated with CaCO 3 alone (189 mAh g -1 ). Furthermore, CaCF-KOH demonstrated enhanced cycling stability, maintaining 102% of its initial capacity after 500 cycles. These results highlight the effectiveness of the catalyst-assisted carbonization pathway in tailoring the microstructure of rCFs and underscore the potential of the optimized rCF as a high-performance, structurally stable anode material for next-generation LIBs.