Mild Expansion Treatment Of Graphite And Its Application As Anode Material In Lithium Ion Battery

Based on our investigation and analysis on the current condition of the field ofboth carbon and non-carbon anode materials in lithium ion battery, carbon materialswill continue to dominate the market of anode materials in lithium ion battery for along time. However, it is undeniable that some problems about graphite anodematerial, including low theoretical capacity and high irreversible capacity in the firstcycle, have always been obstructing its further development, and there is still a longway to go before meeting the demand of electric automobiles. In this thesis, wesynthesized several kinds of graphite intercalation compound using natural flakegraphite, natural microcrystalline graphite and artificial graphite as raw materials andperchloric acid and concentrated sulphuric acid as intercalating agents. Then theas-synthesized graphite intercalation compound was deintercalated, namely mildlyexpanded under different temperature of heat treatment according to its property. Thedefect structure was introduced through the decompose of intercalating agent, whichwill provide extra space to store lithium ion and buffer the volume expansion duringcharging and discharging, therefore improving the capacity, cycling and rateperformance of graphite anode.In this thesis, mildly expanded graphite was synthesized with perchloric acid asboth intercalating and oxidizing agent and natural flake graphite as raw materialthrough chemical intercalating method and following heat treatment. Discussion wasalso made about the influence of reaction time, reaction temperature, washing processand deintercalating temperature on the performance of mildly expanded graphite asanode material in lithium ion battery. The optimum parameters are as follows:120℃reaction temperature,30min reaction time,200℃deintercalating temperature.When used as anode material in lithium ion battery, it showed capacity of395mAh/g under0.2C current density and260mAh/g under1.6C current density,which are much higher than those of natural flake graphite.In addition, mild expansion was also applied to natural microcrystallinegraphite and artificial graphite. Influence of different graphite and different intercalating agents on the electrochemical performance of mildly expandedgraphite was discussed, and a brief description was made about theintercalating mechanism of different graphite. Our results showed thatconcentrated sulphuric acid intercalated microcrystalline graphite presentsrelatively good performance. Its capacity was385mAh/g under0.2C currentdensity and326mAh/g under1.6C current density, much higher incomparison with natural microcrystalline graphite. What’s more, it alsoshowed improved columbic efficiency in the first cycle and avoided too muchsacrifice of volume capacity due to volume expansion.