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JMEPEG https://doi.org/10.1007/s11665-018-3156-6

Soluble Graphene Nanosheets from Recycled Graphite of Spent Lithium Ion Batteries Liangliang Zhao, Xiya Liu, Chuanyun Wan, Xiangrong Ye, and Fanhong Wu (Submitted January 22, 2017; in revised form October 26, 2017) Soluble graphene nanosheets are fabricated from recycled graphite of spent lithium ion batteries through a modified Hammers process followed by deoxygenation with NaOH–KOH eutectic. Ultrasonic exfoliation in N-methyl-pyrrolidone indicates the loosened graphene layers in recycled graphite are prone to exfoliation. Reduction of the exfoliated graphene oxide sheets was conducted in molten NaOH–KOH eutectic at different temperatures. The results show that molten NaOH–KOH effectively eliminates the unsaturated oxygen-containing moieties from the exfoliated graphene oxide sheets while creating more hydroxyl functional groups. Higher temperature treatment is more prone to remove hydroxyls while producing the shrinkage on the surface of graphene sheets. Graphene sheet with a good solubility is produced when the graphene oxide is heat-treated at 220 °C for 10 h. After reduction, the graphene oxide sheets exhibit excellent dispersibility or solubility in water, ethanol and other polar solvents, therefore being highly desirable for solution processing of graphene materials. Such study not only identifies a high-quality stockpile to prepare soluble graphene but also paves a feasible alternative of graphite recycling from spent lithium batteries. Keywords

recycled graphite, soluble graphene, spent lithium ion battery

1. Introduction Graphene, a single-atom thick carbon sheet with sp2 structure of covalent carbon–carbon lattice, has received intensive attention due to its fascinating mechanical, electronic, thermal and chemical properties being potential for composites, sensors, microelectronic devices, thin film and other applications (Ref 14). In order to process graphene materials, dispersing or dissolving graphene in organic or inorganic solvents is necessary. However, due to the strong dispersion force between hydrophobic graphene plates, graphene displays a limited dispersity or solubility in most solvents, especially in water (Ref 5-7). Although certain high boiling point solvents such as N-methyl-2-pyrrolidone could help the dispersion or dissolution of graphene at elevated temperature, the accompanying lowvolatility of these solvents makes it difficult and costly to fabricate the resultant graphene dispersion or solution into sheets or other designed forms (Ref 8). Even if water-soluble molecules or polymers could solubilize chemically reduced graphene, the presence of these foreign species inevitably deteriorates the original properties of graphene (Ref 9-11). It is therefore highly desirable to produce relatively pure yet readily dispersible Liangliang Zhao, Xiya Liu, Chuanyun Wan, and Fanhong Wu, School of Chemical and Environmental Engineering, Shanghai Institute of Technology, Haiquan Road 100, Shanghai 201418, PeopleÕs Republic of China; and Xiangrong Ye,