Tuning the morphologies of fluorine-doped tin oxides in the three-dimensional architecture of graphene for high-performance lithium-ion batteries

Abstract

The morphology of electrode materials plays an important role in determining the performance of lithium-ion batteries (LIBs). However, studies on determining the most favorable morphology for high-performance LIBs have rarely been reported. In this study, a series of F-doped SnOx (F–SnO2 and F–SnO) materials with various morphologies was synthesized using ethylenediamine as a structure-directing agent in a facile hydrothermal process. During the hydrothermal process, the F–SnOx was embedded in situ into the three-dimensional (3D) architecture of reduced graphene oxide (RGO) to form F–SnOx@RGO composites. The morphologies and nanostructures of F–SnOx, i.e., F–SnO2 nanocrystals, F–SnO nanosheets, and F–SnO2 aggregated particles, were fully characterized using electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Electrochemical characterization indicated that the F–SnO2 nanocrystals uniformly distributed in the 3D RGO architecture exhibited higher specific capacity, better rate performance, and longer cycling stability than the F–SnOx with other morphologies. These excellent electrochemical performances were attributed to the uniform distribution of the F–SnO2 nanocrystals, which significantly alleviated the volume changes of the electrode material and shortened the Li ion diffusion path during lithiation/delithiation processes. The F–SnO2@RGO composite composed of uniformly distributed F–SnO2 nanocrystals also exhibited excellent rate performance, as the specific capacities were measured to be 1158 and 648 mA h g−1 at current densities of 0.1 and 5 A g−1, respectively.