Electrochemical performance of graphene-coated activated mesocarbon microbeads as a supercapacitor electrode

Hybrid activated carbon/graphene materials are prospective candidates for use as high performance supercapacitor electrode materials, since they have the superior characteristics of high surface area, abundant micro/mesoporous structure due to the presence of activated carbon and good electrical conductivity as a result of the presence of graphene. In this work, the electrochemical performance of facile and low-cost graphene-coated activated mesocarbon microbeads (g-AM) is carefully studied. The results show that g-AM can only be formed at a very high temperature over a long activation time, resulting in the formation of a large pore size and low specific surface area, further resulting in poor electrochemical performance (110 F g^-1 at 0.1 A g^-1 in 6 M KOH solution). Ball milling for a short time is an effective way to improve the electrochemical performance (191 F g^-1 at 0.1 A g^-1 in 6 M KOH solution). Moreover, due to the strong resistance to aggregation and good electrical conductivity of graphene flowers, the g-AM had nearly 100% rate capability when increasing the current density from 5 to 50 A g^-1. The as-assembled two-electrode symmetric supercapacitor exhibits a high energy and power density (5.28 W h kg^-1 at 10 000 W kg^-1) in organic LiPF₆ electrolyte, due to its better electrical conductivity. It is expected that this type of hybrid structure holds great potential for scalable industrial manufacture as supercapacitor electrodes.