High-performance Li-ion batteries based on graphene quantum dot wrapped carbon nanotube hybrid anodes

Since Akira Yoshino first proposed the usage of the carbonaceous materials as an anode of lithium ion batteries (LIBs) in 1985, carbonaceous materials such as graphite and graphene have been widely considered as LIB anodes. Here, we explored the application of novel carbonaceous LIB anodes incorporating graphene quantum dots (GQDs). We fabricated a freestanding all-carbon electrode based on a porous carbon nanotube (CNT) sponge via a facile in-situ hydrothermal deposition technique, creating coaxial structure of GQD-coated CNTs (GQD@CNTs) through electrostatic interaction and π-π stacking with tunable loading and functionalization. This hybrid structure combined conductive CNTs with highly active GQDs, in which GQDs with predesigned functional groups provided massive storage sites for Li ions and the 3D CNT frameworks avoided the agglomeration of GQDs, together contributing to a high specific capacity (700 mAh·g^-1 at 100 mA·g^-1 after 100 cycles) and rate performance. Even at a high current density of 1,000 mA·g^-1, the reversible specific capacity remained at 483 mAh·g^-1 after 350 cycles. In particular, the mechanism study demonstrated the important role of oxygen functional groups of GQDs in promoting the performance of the LIB anodes by controlled grafting of GQDs onto various porous-carbon and metal-foam based structures.