Preparation And Performance Of Lithium-ion Battery Anode Materials And Applied Research

Advanced rechargeable lithium ion batteries are attractive for use in consumer electronic and electric vehicle (EV) application because of a favorable combination of voltage, energy density, cycling performance, self-discharge ratio and environmental protection. The development of lithium ion batteries and carbon anode materials are reviewed in detail. Much attention is attached to the further improvement on performance of lithium ion batteries and reduction in their cost. There are a great variety of carbon materials available, while they have been investigated as anodes of lithium ion batteries for only several years, so it is necessary and important to develop carbon materials of excellent performance and low cost.The structures and characteristics of several graphite samples are measured by means of powder X-ray diffraction (XRD), Brunauer-Emmer-Teller (BET) surface area measurement, inductively coupled plasma (ICP) spectroscopy, particle size analysis and electrochemical measurements. The effects of origin, structure, impurity, particle size, specific surface area of carbon materials on the electrochemical characteristics are studied. A synthetic graphite with abundant resources, low cost and favorable performance is determined as the raw material for modification of graphite.Improved graphite anode for lithium ion batteries is obtained by heat-treatment of synthetic graphite. As the temperature and the soak time increasing, crystallite size, graphitic degree and average particle size of the graphite increase, while specific surface area decreases. The electrochemical performance of modified graphite is improved with the change in structure and surface characteristics. Li or Al is doped into graphite before heat-treatment and exists in the form of CH3COOLi or A1D3. The electrochemical characteristics of graphite anode doped with Li or Al are further enhanced. Compared with the lithium ion batteries using untreated graphite as anode material, those using modified graphites as anode materials have larger capacity, higher discharge voltage and better cycling capability. The lithium ion batteries with Li doped graphite anodes have the best performance.Disordered carbon materials are prepared by pyrolysis of sugar and phenol resin at high temperature. As the temperature of pyrolysis and the soak time increasing, the carbon materials become more stacked, the specific surface area reduces, both reversible capacity and irreversible capacity decrease, the initial coulumbic efficiency increases, and the hysteresis in the voltage profile between charge and discharge is cut down. The results show that structure and performance of carbon material are affected by heating rate and pattern. The process parameters for pyrolysis of sugar and phenol resin are optimized.Carbon materials with disordered carbon/graphite composite structure, produced from synthetic graphite coated with large molecule polymer and pyrolyzed at high temperature, are investigated as anodes for lithium ion batteries. The graphite is covered with a thin film of disordered carbon according to the measurements of XRD, BET, particle size analysis and scanning electron micrographs (SEM). Sugar and phenol resin are used as the precursors of the shell-carbon materials. Structure and performance of composite structure carbon material are studied in detail. Silicon is doped into the shell-carbon material by coating the graphite with mixture of phenol resin and polysilicone and pyrolyzing at high temperature. Electrochemical measurements of Li/C cells and lithium ion batteries show that composite carbon materials coated with appropriate amount of sugar or phenol resin have improved charge/discharge andcycling performance, and the composite carbon material doped with silicon has better performance than that of carbon materials coated with phenol resin.Meso-carbon microbeads (MCMB) is prepared from coal tar though polymerization, separation, carbonization, graphitization. By the addition of carbon additive and adoption of optimized conditions...