Functionalized Graphene Nanosheets with Fewer Defects Prepared via Sodium Alginate Assisted Direct Exfoliation of Graphite in Aqueous Media for Lithium-Ion Batteries

We proposed a cost-efficient method to produce graphene nanosheets from graphite by using a high shear mixer in an aqueous sodium alginate (SA) solution. The results from transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis revealed that the graphite was successfully exfoliated into graphene nanosheets, the obtained graphene was modified by SA after exfoliation, and improved dispersion in water was achieved. The concentration of graphene could attain 0.60 mg/mL at a graphite concentration of 15 mg/mL. When used as nanofiller, significant increases of 65% and 73% in the tensile strength and storage modulus, respectively, of poly(vinyl alcohol) were achieved by incorporating only 0.5 wt % graphene nanosheets. When the exfoliated graphene was applied as an electrode material for lithium-ion batteries, a high initial reversible discharge capacity of 1450 mAh/g was obtained at 100 mA/g, and the capacitive contribution made up about 20.1% at 1 mV/s, suggesting that the unique structure of graphene nanosheets exhibited excellent electrochemical performance.