The Syntheses, Structure And Properties Of Sn-based/C Composites Anode Materials For Lithium-ion Batteries

Tin-based materials with a high specific capacity have potential development and application prospects as a new type of lithium-ion battery anode materials. But the huge volume expansion and the large initial irreversible capacity in the process of charging and discharging limit the application of tin-based anode materials in commercial production. High-energy ball milling as well as CVD are applied in this thesis in order to reduce the size of SnO2 and prepare the carbon coating Sn/SnO2/C composites. Moreover, glucose and tin chloride are used as the starting constituents to prepare Sn-based/C composites, and high conductive graphite and acetylene black are introduced into the composites during the solution process. The effect of the fabrication technique and its parameters on the structure and electrochemical properties and the correlation of the structure and electrochemical properties of composites were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopyand element analysis, etc. and eletrochemical testing of galvanostatic charge-discharge, cyclic voltammograms, electrochemical impedance spectra, etc. The key factors that influence the cycle stability of composites and its mechanism are also discussed.The results show that ball milling can effectively refine and dispersethe SnO2 particles, reducing the charge and discharge volume expansion and hence improving the cycle stability. But too long ball milling time makes the crystallization of SnO2 poor, reducing the capacity of the SnO:anode. The first coulombic efficiency and cycle stability have been improved by the carbon coating of the SnOo by chemical vapor deposition, in which Sn/SnO2/C composite is formed.Sn-based/C composites are synthesized successfully by a solution method by using glucose and tin chloride as raw materials. SnO2 particles obtained at low calcination temperature and Sn particles obtained at high calcination temperature all have super fine size of several nanometer. The capacity of the composite decreases and the cycle stability increases with the increase of the addition of glucose. Among the composites obtained, the one from a molar ratio of 1:1 of glucose to tin chloride as starting material with 5 wt.%graphite addition and calcined at 500℃provides high overall electrochemical properties, possessing a high reversible capacity of 520 mAh-g"1 and a capacity of 350 mAh-g-1 after 100 cycles. The SnO2/C composite calcined at low temperature of 400℃displays low cycle stability due to the the loworder of the carbon. Whearas with the increase of the calcination temperature, the composite has low amount of Sn, which has high capacity, resulting in a low capacity. But as the content and the order of the carbon increases, the cycle stability of the composites increases.The addition of graphite effectively improves the capacity and the cycle stability due to that it can reduce the particle size of the composites.But as the low capacity of graphite, too much addition of graphite reduces the capacity of the composite. Compared with the addition of graphie, the addition of acetylene black can possess high capacity and high cycle stability. The Sn/SnO2/C composite prepared with glucose to tin chloride in a molar ratio of 1:1 with 5wt.%acetylene black and calcined at 500℃possesses a capacity of 411 mAh-g-1 after 100 cycles, which is attributed to the high conductivity and the small particle size of acetylene black.