Efficient Preparation, Structures And Electrochemical Properties Of Graphene Nanosheets From Mesophase Pitch

Graphene nanosheets (GNSs) were prepared using mesophase pitch as raw material by vacuum carbonization. The structures and electrochemical properties of the resulting GNSs as anode material for lithium-ion battery were studied, and the influences of carbonization temperature, vacuum degree, heating rate, additive content on their structures and electrochemical properties were investigated. In addition, the electrochemical properties of the GNSs were improved by performing the treatments including ball milling and intercalation-expansion processes.The structures of the GNSs were characterized by XRD, FESEM, TEM, Raman and N2 absorption-desorption, and the effects of vacuum carbonization process on the structures of the GNSs were studied. Results show that graphite flakes with a network structure are formed from the precursors of GNSs during high temperature treatment, and then changed into transparent graphene nanosheets with a stacked lamellar and wrinkled structure. The optimum conditions for preparing the GNSs are as follows: carbonization temperature 1800℃, vacuum degree 700Pa, heating rate 20℃/min and additive content 50%.The influence of ball milling process on the structures of the GNSs was investigated by Raman, TEM and N2 adsorption-desorption, and the effect of intercalation-expansion process on the structures of the GNSs was studied using XRD, TEM and FESEM. Results show that the ball milling process is beneficial for the further exfoliation of GNSs. The optimum conditions for preparing the GNSs are as follows:milling time 4h, milling rate 600r/min, ball feed ratio 648.5:1. In addition, the GNSs, treated with the intercalation-expansion process, have less graphene layers and larger interlayer spacing than parent GNSs.The electrochemical properties of the GNSs prepared by vacuum carbonization were studied using LAND battery testing system, and the effects of ball milling and intercalation-expansion processes on the electrochemical properties of the GNS were investigated. Results show that the GNS prepared by vacuum carbonization have good electrochemical properties, as indicated by that the initial charge capacity, discharge capacity, and coulombic efficiency of the GNSs at a current density of 10mA·g-1 are 566mAh·g-1,360mAh·g-1, and 63.6%, respectively. In addition, both the ball milling process and the intercalation-expansion process favor the improvement of the electrochemical properties of the GNSs, especially at high current densities. When the current density is 1000mA·g-1, the discharge capacities after 20 cycles of the GNSs treated by ball milling and intercalation-expansion processes maintain 528mAh·g-1 and 253mAh·g-1, respectively.