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(-) (sic) Li4.4Sn reaction), owing to the reversibility of the reaction between Sn and Li2O to form SnOx (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. (C) 2018 Elsevier B.V. All rights reserved.