Preparation And Electrochemical Properties Of Sn-based As Anode Materials For Lithium Ion Battery

Lithium ion batteries have been used in mobile phones, digital cameras, notebook computers, electric vehicles, military equipment, aerospace and other popular fields, owing to their small volume, light weight, no memory effect, high energy density, small self-discharge flow, wide working temperature range, high safety, can be large current charge and discharge, cycle times, long cycle life and so on.In this paper, we synthesized tin-based materials including SnO2, SnO2/C, NiO-SnO2 by a simple hydrothermal method, and researched the electrochemical performances as anode materials of lithium ion batteries. Furthermore, we can compare the difference of their electrochemical performances among the three kinds of materials as anode materials. Carbon coating composite combined with the advantage of nanomaterials and carbon, the synergistic effect between the metal oxides applied to the metal oxide composite, which are expected to meet the needs of the development of lithium ion batteries. This thesis mainly studies follows:1、We synthesized pure SnO2 nano material via a hydrothermal method. Its phase, structure and morphology were tested by SEM(scanning electron microscope) and XRD(X-ray diffraction). And then the constant current charge and discharge, cyclic voltammograms(CV) and alternating-current impedance(EIS), electrochemical performance were measured as an anode material for lithium-ion battery. XRD proved that SnO2 prepared in this experiment can be assigned tetragonal rutile; SEM photograph shows that the SnO2 is in nanoscale. Cyclic voltammograms reveals the process of the intercalated-li SnO2 materials, the, so that the mechanism of the reaction process was determined.2、Different proportions of SnO2/C composite materials were prepared by one step hydrothermal method due to its poor conductive and serious effect in volume as anode for lithium ion battery. And the introduction of carbon materials in promoting the specific capacity and cycle performance was analyzed. The materials structure and morphology, phase and carbon content were then characterized by SEM, XRD, and TG(thermogravimetric) analyses. Electrochemical tests were performed which included the constant current charge and discharge, EIS. The composite was composed of amorphous carbon and nanocrystalline SnO2 by XRD analysis, and the content of carbon was calculated according to the themogravimetric analysis. SEM images revealed that the diameter of these as-prepared spheres varied from 50 to 60 nm. The electrochemical results showed that SnO2/C nanocomposite could achieve 1197.5 mAh·g-1 reversible capacity and 55.1% initial coulombic efficiency, and 190 mAh/g capacity retention after 50 cycles compared to the SnO2 nanoparticles of 940.6 mAh·g-1. These improvements can be ascribed to the carbon, which can enhance the conductivity of SnO2, suppress the aggregation of active particles, and increase their structural stability during cycling.3、NiO-SnO2 nano composite materials were prepared by a hydrothermal. Series of tests were realized in SEM, TEM(transmission electron microscope), XRD and TG on the structure, phase and morphology. In addition, the constant current charge and discharge, cyclic voltammograms and EIS were used to measure the electrochemical performance of the materials as an anode for lithium ion batteries. From SEM, it can be seen that the size of the primary NiO-SnO2 particles is 30~40nm. XRD patterns showed that all the diffraction peaks can be indexed to crystalline SnO2 and NiO. High specific capacity and good cycle performance were obtained according to the electrochemical tests, because the synergistic effect between SnO2 and NiO increased the stability of the materials, enhanced electrical conductivity and was advantageous to the lithium ion diffusion. Nano-sized Ni elemental generated during the process of charge and discharge, which increased the number of atoms on the surface of active substance and electrochemical reaction activity. Further more, Ni elemental can react with Li2 O because of its high activity, and make Li2 O generated in the first discharge process into Li+ reversibly, then the anode capacity increased. Accordingly, the irreversible capacity reduced and the coulomb efficience improved. EIS test was further evidenced that the electrical conductivity of the materials was greatly enhanced due to the interaction between NiO and SnO2, and its dynamics in the process of charging and discharging characteristics were significantly improved.