Revisiting the conversion reaction in ultrafine SnO₂ nanoparticles for exceptionally high-capacity Li-ion battery anodes: The synergetic effect of graphene and copper

Generally, in SnO₂-based anode materials, the reversible alloying/dealloying reaction is the main Li-ion storage mechanism. Interestingly, these materials can show an exceptionally high capacity that is beyond the theoretical value (i.e., 783 mA h g⁻¹ based on Sn + 4.4Li⁺ + 4.4e⁻ ⇌ Li_4.4Sn reaction), owing to the reversibility of the reaction between Sn and Li₂O to form SnO_x (x = 1, 2), so-called conversion reaction. Herein, we prepare Cu-reduced graphene oxide (rGO)-SnO₂ nanocomposites as a model system in order to demonstrate an effective strategy to improve the reversibility of the conversion reaction in SnO₂. The incorporation of rGO can prevent the aggregation of SnO₂ nanoparticles. Furthermore, the Cu-rGO-SnO₂ nanocomposite exhibits the most improved conversion reaction reversibility, resulting in improved cycling performance and high capacity. Ex-situ transmission electron microscopy analysis confirms the high reversibility of the conversion as well as the alloying/dealloying reactions. Also, Cu nanoparticles promote the decomposition of amorphous Li₂O, leading to enhancement of the conversion reaction between Sn and Li₂O. Therefore, these results demonstrate a strategy for significantly improving the electrochemical performances of SnO₂-based anodes for Li-ion batteries.