Cyclability Improvement of Recycled Graphite Materials in Lithium-Ion Batteries Via Conductive Polymer Coating
Authors: Miao Qiusu , Zhu Tianyu , Jin Xiuyu , Fang Chen , Liu Gao 
Published: August 2024

In recent years, lithium-ion batteries have been widely adopted in electric vehicles and electronics. However, the growing number of retired lithium-ion batteries poses a significant environmental challenge, generating substantial material waste and potential pollution. In most commercial batteries, graphite is the prevalent choice for anode material, owing to its high electrical conductivity and mechanical stability. Therefore, recycling graphite from spent lithium-ion batteries is a potential solution to eliminate the waste and meet the increasing demand.

While considerable attention has been directed toward recovering metallic components of the spent lithium-ion batteries, limited effort has been dedicated to recycling graphite. Some previously developed methods include the pyrometallurgy process and hydrometallurgy process. However, due to high energy consumption and environmental pollutions, these methods have not been applied in large scales. Additionally, graphite particles have experienced various aging mechanisms during charge and discharge cycles, such as the formation of a solid electrolyte interface (SEI) and the intercalation of solvent molecules, potentially leading to structural alterations and degradation. Hence, it is advisable to implement surface treatment to enhance capacity stability if the recycled graphite does not perform optimally following the recovery treatment.

In this study, we developed a simple process to recycle spent graphite utilizing aqueous and organic wash with N-Methylpyrrolidone (NMP) and toluene, followed by surface coating with the conductive polymer poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic ester) (PFM). The surface coating served as a protective layer of graphite particles and a charge transport agent to enhance conductivity. The morphologies and structures of the pristine, recycled, and PFM-coated recycled graphite samples were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis.

To investigate the impact of employing PFM as a binder, electrochemical tests were done using anodes with both recycled graphite and PFM-coated recycled graphite. In recycled-graphite||NMC532 full cell testing, cells with PFM-coated recycled graphite exhibits higher coulombic efficiency (>99.90%) than cells without PFM coating at a rate of 0.33 C. A capacity retention of 77.49% was achieved for PFM-coated cells after 300 cycles, whereas the ones without coating have a capacity retention of 70.21% in average. Rate tests were also conducted on both the cells with and without PFM-coating. It shows that both types of cells support high-rate cycling. About 85% of charge capacity was delivered for cycling at 1 C for both cells with and without PFM-coating.

Overall, the recycling method can be easily operated with minimal waste production, low energy consumption, and low economical costs. The PFM coating on the recycled graphite particles leads to enhancement of mechanical strength and efficiency in battery cycling.

Fig. A, The process scheme of recycling graphite; B, Pictures of an electrode from spent lithium-ion batteries (left) and an electrode fabricated with recycled graphite (right); C, Capacity retention of recycled graphite without PFM coating (blue) and with PFM coating (green); D, Coulombic Efficiency of recycled graphite without PFM coating (blue) and with PFM coating (green).

Figure 1