Extra Li-Ion Storage and Rapid Li-Ion Transfer of a Graphene Quantum Dot Tiling Hollow Porous SiO₂ Anode

Graphene is widely used to enhance the electrochemical performance of anodes. However, graphene tends to be vertical with the lithium-ion (Li+) diffusion direction, and a few heterointerfaces are formed between graphene and active materials by point-to-point contact. Herein, a graphene quantum dots (GDs) tiling hollow porous SiO2 (HSiO2@GDs) anode is predicted by density functional theory (DFT) and is achieved by experiments. Due to the ultrasmall size, the tiling of GDs would provide Li+ a rapid diffusion channel and abundant heterointerfaces (face-to-face contact) between the GDs and the hollow porous SiO2 (HSiO2). Moreover, owing to the higher electrostatic potential of SiO2, the large-scale local electrical field from GDs to HSiO2 is established at the heterointerfaces, which provide extra Li+ storage sites and further facilitate the Li+ transfer. To our knowledge, the HSiO2@GDs shows the highest specific capacities at various current densities (such as ∼1100 mA h/g at 5 A/g and ∼2250 mA h/g at 0.2 A/g) among reported silicon oxides anodes and presents excellent cycling stability (∼1000 mA h/g after 2000 cycles at 3 A/g). Moreover, the design idea is available to design other widely studied graphene-containing anodes such as the Si, SnO2, TiO2, and MoS2.