| With the increasing demand of energy, decreasing reserves of fossil fuel and the aggravation of environmental pollution, people focus on development of clean and high efficiency energy. As an energy storage device, lithium ion battery has been extensively utilized in portable equipment for its high capacity, long life, portability and environmental friendly. The key point of influency of lithium ion battery properties is its electrode material. Most of the negative electrodes of commercialized lithium ion battery are made of graphitic carbon which already cannot satisfy people’s demand. Therefore research and exploitation of new negative material of lithium ion battery becomes an important issue.Due to the high theory capacity and fairly security, tin-based material has become one of the hottest spot of new negative material investigation in recent years. But the severe volume effect of tin-based material could happen in Li+intercalation/deintercalation process which caused the pulverization and exfoliation of material and attenuation of electrode performance. The performance improvement methods of tin-based material mainly include preparation of tin-based alloy material, composite material and nano material. The research content of this dissertation is mainly about designation of new tin-based material for negative electrode of lithium ion battery with recent improvement method. The main content is as follows:There is a systematic survey of negative material of lithium ion battery in chapter one. Firstly, the brief summary of development history, principle and characteristic of lithium ion battery were provided. The research progress of negative was described in detail after that. Negative electrode material of lithium ion battery can be classified as four categories according to the different characteristic of lithium insertion. They are interlayer or surface lithium storage material (e.g. carbon material), alloying lithium storage material (e.g. Si, Sn), zero or low-strain lithium storage material (e.g. Li4Ti5O12, TiO2) and oxide lithium storage material.The characteristic, preparation method, existing problem and improvement idea of the four categories were discussed after that. On the basis of above survey, the working idea and research contents was enduced.The major content of chapter three is about new improvement method of tin-based alloy material. We offered electrodeposition and dealloying method for this topic. At first, the composition and preparing method of electroplating bath were determined and experiment condition of electrodeposition and electrochemical dissolution were studied at the same time. After that the as-plated and porous Sn-Cu, Sn-Co and Sn-Ni alloy with appropriate proportion were successfully prepared in this condition. It is believed that the porous structure with different configuration would be formed in electrochemical dissolution process from the results of morphology change of the alloy before and after electrochemical dissolution. The size of the pores is from tens to hundred of nanometers. The structure of material is related to type, composing and preparation of alloy. It can be found that there is lot of Sn phase in obtained tin-based alloys from their XRD results and most of them were lost after electrochemical dissolution. So the formation of porous structure is mainly result from the dissolution of Sn phase. The cyclic voltammetry performance of as-deposited and porous tin-based alloy proved the different reaction mechanism caused by changes of composition. The charge and discharge curves of as-deposited and porous tin-based alloy proved the weaker polarization of electrode in porous alloys. The higher specific capacity, better electrochemical stability and rate capability of porous alloys can be exhibited in cyclic charge-discharge test. It is believe that the enhancement of electrochemical performance is mainly due to adaptation of volume expand, optimized contact between electrode and electrolyte and shorter transfer distance. So the porous tin-based alloys prepared by electrodeposition and dealloying possess of advance electrochemical performance.The research content of chapter four is focus on tin oxide material. Three kinds of tin oxide and graphene composites were designed for optimize their electrochemical performance. The ethylene glycol microwave processing and one-step hydrothermal are used for synthesis tin oxide-graphene composite (SnO2-rGO) and two kinds of tin oxide-graphene aerosol composite (SnO2-GA and SnO2-NGA) respectively. The planar structure of SnO2-rGO was confirmed by experiment. Tin oxide nanoparticles loaded on the surface of graphene possess size of14-17nm and even distribution. The loading amount is about40%. The three-dimensional macroporous structure and tin oxide loading statue of SnO2-GA and SnO2-NGA were characterized by experiment. The size of tin oxide is smaller than10nm and the loading amount is more than60%. Their Raman spectra proved the less layer-numberd structure of graphene, higher flaw degree of N-doped graphene and the variety electron distribution caused by the combination of tin oxide and graphene. Few oxygen-containing groups can be detected by XPS technique and the elements valence states were confirmed at the same time. Three composite materials were tested by cyclic voltammetry and the reversibility of the first lithiation step was testified. The combination of tin oxide and graphene can relieve the stack of graphene nanoplate, agglomeration of tin oxide nanoparticle, fit into volume expansion and ensure high conductivity. So the excellent performance showed in electrochemical test. In addition, an enhancement performance can be found in SnO2-NGA for strengthen of conductivity of material and binding capacity between SnO2nanparticle and graphene from N-doping. Beside that, Li+pass through graphene allowed by the flaw produced by N-doping is another important factor. |
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