Wrapping SnO₂ with porosity-tuned graphene as a strategy for high-rate performance in lithium battery anodes

The previous studies on SnO₂ as electrode materials convey a message that the inevitable pulverization of SnO₂ particles can be resolved by carbon-based materials. Since graphene has also proved effective for the harmful decrepitation of the particles with an advantage of electronic conductivity, wrapping SnO₂ by sufficient amount of graphene seems to be an answer to enhancing its cycle life. On the other hand, severe wrapping of SnO₂ by graphene is deleterious to its rate capability due to the sluggish motion of Li⁺ through the stacked graphene layers. Thus, in order to make graphene sheets favorable for Li-ion diffusion, they were modified to have large porosity with 3-D architectures, by a simple heating-rate control. The porous graphene-wrapped SnO₂, having direct diffusion channels for Li⁺, outperforms the SnO₂ with less-porous graphene. Consequently, the excellent performances are fulfilled, showing both stable cyclability (∼1100 mAh g^-1 up to 100 cycles) and high rate capability (∼690 mAh g^-1 under 3600 mA g^-1). This strategy using porosity-tuned graphene sheet furnishes a valuable insight into the effective encapsulation of active materials, especially for those undergoing pulverization during cycling.