The self-assembly of porous microspheres of tin dioxide octahedral nanoparticles for high performance lithium ion battery anode materials

The self-assembly of tin dioxide (SnO₂) porous microspheres was conducted via a surfactant-free one step hydrothermal reaction. The crystalline structure and morphologies of the as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the porous microspheres consist of single crystalline SnO₂ octahedral nanoparticles approximately 40 nm in width and 60 nm in length, with exposed high index {221} facets. The as-prepared porous nanostructure was used as an anode material for a lithium ion battery, whose cyclic voltammetry, electrochemical impedance, charge-discharge galvanstatic behavior and cycle performance were examined. A highly stable capacity about 690 mA g^-1 after 50 cycles at a current density of 500 mA g^-1 was achieved, which is much higher than that of non-assembled SnO₂ octahedral nanoparticles and irregular SnO₂ nanoparticles. The superior electrochemical properties result from the preferable nanostructure, with the pores favorable to the diffusion of electrolyte and providing buffer space for the volume change during alloying and dealloying reactions. Meanwhile, the special crystalline facets of the octahedral nanoparticles can facilitate Li⁺ ion insertion and extraction.