Study On The Pitch Carbon Coated Graphite Anode Materials By Vacuum-liquid Phase Method

Lithium ion battery is honoured as the "most competiti ve power source in the 21 st century ", because it has the advantages including high voltage, high specific energy, low self-discharge, environment friendly, no memory effect. Graphite is considered as the highest commercial valuable anode material because of its high specific capacity, good cycle performance, low insertion and extraction of lithium platform. However, more SEM films are formed as a result of the poor compatibility of graphite and organic electrolyte. Excessive SEM films not only waste more l ithium to cause more irreversible capacity loss, but increase boundary impedance and impede electrochemical kinetic to induce the cleavage or desquamation of graphene. As a consequence, capacity is reduced and cycling performance is decreased.Therefore, in order to improve the performance of the graphite anode material, vacuum- liquid phase method was used to coat the pitch carbon on two kinds of graphite. XRD, SEM, galvanostatic charge-discharge and other methods were used to study the influence of modified and medium pitch carbon coating on crystal structure, surface morphology and electrochemical properties.The results show that: vacuum- liquid phase coating method can prepared "core-shell" structured carbon-coated graphite. Species and coating amount of pitch carbon had a great influence on the structure and electrochemical performance, while microcrystalline graphite coated by medium pitch and artificial graphite coated by modified pitch formed a favorable amorphous carbon coating layer on graphite particle surface, improved electrochemical performance of graphite material. With the increase of coating amount, the aggregation degree of graphite particle increased and the flatness of surface enhanced. Coating modification can improve the initial coulombic efficiency and not change reversible capacity basically. Coated effect is poorer, while microcrystalline graphite coated by modified pitch and artificial graphite coated by medium pitch. The medium pitch carbon coating amount of microcrystalline graphite was 6%. The modified pitch carbon coating amount of artificial graphite was 9%. The higher the concentration of pitch, the better the electrochemical performance of the coated microcrystalline graphite is achieved. The optiumun pitch concentration of 0.1g/ml was chosen. Carbonization heating rate can also affect the electrochemical performance of the coated microcrystalline graphite. Both slow and fast rate can not improved the electrochemical performance. The best carbonization heating rate is 2?/min. The higher the carbonization temperature, the better the electrochemical performance of the coated artificial graphite is achieved. The optiumun carbonization temperature of 1100? was chosen. The modification effect by vacuum – liquid phase method was superior to solid phase method. After coating modification, electrochemical performance of graphite materials had been improved significantly, microcrystalline graphite and artificial graphite initial coulombic efficiency increased from 86.5% and 90.0% to 92.7% and 93.4%,cycling performance enhanced considerably.