Preparation And Electrochemical Performance Of Porous SnO₂ Nanospheres And Its Composite Structure With Graphene

SnO2 is an important tin-based chalcogenide and have excellent properties of optical, catalytic, electrochemical, magnetic and gas sensing etc., having a wide range of applications in the fields of gas sensors, photoelectric detectors, photoconductive materials, photocatalyst, Li-ion batteries, solar cells and so on. As an anode material for Li-ion batteries, due to the huge volume change of SnO2 during the process of charge-discharge, large internal stress is created, leading to the disintegration of the electrode material. Constructing porous or hollow structure is a effective strategy to overcome so-called "volume effect" problem for SnO2 anodes. The composite structures made by SnO2 nanostructure and graphene with high mechanical strength can be further improved the cycling performance of anode materials. First, with controlled reaction conditions, we successfully synthesized porous hollow SnO2 nanosphere; second, we used an in-situ reduction method to obtain porous SnO2 nanosphere/graphene composite structure. The electrochemical performances of two nanostructures and the relationships of electrochemical property and structures were investigate systematically, Including:1. Synthesis and electrochemical properties of porous hollow SnO2 nanospheres.Porous hollow SnO2 nanospheres were prepared through a forced Sn2+ hydrolysis method under hydrochloric acid medium. These hollow nanospheres with an average diameter of 220 nm had a very thin shell thickness of about 40 nm and were surrounded by elongated octahedral-like nanoparticles with the apex oriented outside. The experimental conditions, such as HC1 content, reaction temperature and time directly dominated the morphology, structure and crystallinity of the obtained samples. A pre-oxidation-nucleation-growth mechanism was proposed on the basis of the previous research and time-dependent experiments. Electrochemical tests showed that the porous hollow SnO2 nanospheres exhibited improved cycling performance for anode materials of lithium-ion batteries, which retained a high reversible capacity of 540.0 mAhg-1, and stable cyclic retention at 120th cycle..2. Preparation and electrochemical properties of the porous SnO2 nanospheres/graphene composite structure.The porous SnO2 nanospheres/graphene composite structure was successfully prepared for the first time by an in-situ hydrothermal reduction method via Sn2+ The degree of as-prepared graphene reduction was high, and the SnO2 nanospheres with an average diameter of 220 nm uniformly distributed throughout the surface of graphene. Electrochemical tests showed that the porous SnO2 nanospheres/graphene composite structure can effectively buffer the volume change of lithium ion during deintercalation process, and showed improved cycling performance.