Modification And Electrochemical Properties Of Graphitized Meso-Carbon Microbeads For Lithium-Ion Battery

Since lithium ion batteries were introduced to the market by SonyCompany in the early 1990s, they have seen substantial growth indemand in recent ten years, and have been paid much attention byworldwide researchers and companies, due to their advancedelectrochemical properties. Despite considerable efforts to find othersubstituents, carbon still remains the only commercial anode for thebattery due to its steady structure and good circular properties. Carbon anodes for lithium ion batteries have such advantageousproperties as good charge/discharge reversibility, low discharge platform,high specific capacity, high conductivity, and so on. But the maincommercial carbon anodes have a rather lower specific mass capacity(theoretic specific mass capacity is lower than 372mAh/g) compared withthe metal anodes e.g. tin oxide and a rather high preparation cost. Thestructure and properties of carbon anode are affected by the origin andprocess condition of precursor remarkably. Based on the characteristics IVmentioned above, this thesis was focused on the study of different surfacemodifications of Shanshan graphitized mesocarbon microbeads(SSGMCMB). The preparation parameters, morphologies, structures andelectrochemical behaviors of modified SSGMCMB and their relationswere investigated in order to develop a novel carbon anode with higherproperties, and to prompt the research and commercialization of lithiumion batteries. In this thesis, three methods were used to modify SSGMCMB suchas oxidation, coating, and homogeneous precipitation.Oxidized-SSGMCMBs were obtained through oxidizing SSGMCMBwith pure oxygen and boiling HNO3, respectively. Phenolic Resin (PR)encapsulated SSGMCMBs (PR/SSGMCMBs) were prepared throughresin coating, curing and carbonization at the temperature of 1000℃. Andthe third anode SnO2/SSGMCMB composites were prepared throughhomogeneous precipitation. The microstructure of these anode materialsand their lithium insertion performance were studied by ScanningElectronic Microscopy (SEM), X-Ray Diffraction (XRD),Thermogravimetric Analysis (TG), X-Ray Photoelectron Spectroscopy(XPS), Infrared (IR), and charge-discharge measurements. The mainresearch results of this dissertation are summarized as follows: 1 SSGMCMBs were oxidized by pure oxygen at 550℃and byboiling HNO3 for different time, respectively. The changes of structure, Vsurface functional groups and the electrochemical properties of modifiedSSGMCMB were investigated. The research results showed as follows: (1) Although these two oxidation methods had introduced somefunctional groups with oxygen, and nano-holes or orifices into the surfaceor interlayer of the SSGMCMB, the interlayer structure of theSSGMCMB was not spoiled. The oxidation reaction took place on thesurface or in the interlayer of the graphite, which expanded the distanceof the graphite interlayer to form the structure of oxidized graphite. (2) A discharge platform, appeared at about 0.75V (Vs φLi + /Li) in thefirst discharge curves and disappeared in the second discharge cycle, wasdetected in both SSGMCMB and Oxidized-SSGMCMB anodes, whichcan be attributed to the formation of the Solid Electrolyte Film (SEI). Thecorresponding capacity was called irreversible capacity. A long dischargeplatform appeared at about 0.25V, which was the result of Li insertion tothe interlayer of SSGMCMB. The rather low and long discharge platformis the main reason why graphitized MCMB can be used as thecommercial anode material for lithium ion batteries. (3) The first discharge capacity of oxygen Oxidized-SSGMCMBincreased obviously, and the first irreversible capacity decreased first andthen increased gradually as the oxidation time prolonged at 550℃. TheOxidized-SSGM...