The Effects Of Surface Modifications On The Performance Of A Natural Graphite As Anode Material Of Lithium Ion Batteries

The principle and the development of lithium ion batteries have been described in this dissertation. The physicochemical properties, electrochemical performance and some modification methods of graphite anode have been introduced with emphasis. Basde on this, a natural graphite was modified by solution oxidation using green and efficient oxidants, and the structure and electrochemical performance of modified graphite were investigated.A natural graphite was directly modified with the ferrate (VI) solutions which were prepared by electrolyzing iron wire gauze in 5mol·dm^-3 LiOH, NaOH and KOH solutions, respectively. The oxidated natural graphite displays much larger reversible capacity and better cyclic stability than pristine natural graphite. The improvement effects of various ferrate alkali systems on the performance of natural graphite are different, and the corresponding sequence is NaOH > LiOH > KOH. For the sample oxidated in the NaOH system, its reversible capacity rises from 225mAh/g to 440mAh/g, and it even does not fade after 50cycles.Nature graphite was also modified by Fenton Reagent and hydrothermal reactions in NaClO and Li₂FeO₄ solutions, respectively. The oxidated natural graphite displays much better electrochemical performance than the pristine sample. Its reversible capacity rises from 225mAh/g to 330-350mAh/g, and its electrochemical-cycling stability is also improved.The results of Scanning Electron Microscopy (SEM), Atomic Absorption Spectroscopy (AAS) and Raman Spectroscopy showed that some mesoscopic pores/channels appear on the surface of graphite due to the oxidation treatments, and some products could improve the formation of the Solid Electrolyte Interphase (SEI) membrane on the graphite surface. The pores/channels on the edge plane of graphite can provide more inlets and outlets for the intercalation/deintercalation of lithium, and may also serve as additional lithium storage reservoirs. These changes in the surface structure of graphite may be responsible for the improvement on the performance of the oxidated graphites.