Preparation And Characterization Of Artificial Graphite And Sillicon-Graphite Composite Anode Materials

Abstract:In order to meet the increasing requirements for high energy density, high-rate charge-discharge ability and long-life batteries, two aspects of research were carried out. On the one hand, improving the structure of the artificial graphite to enhance the cycle performance, especially the rate performance of the graphite anode material by controlling the carbonization process; on the other hand, silicon(Si) was compounded with graphite to overcome the application limitation of the low theoretical specific capacity of graphite (372mAh g-1), which can realize complementary advantages and make up each other’s shortcomings, and prepare novel composite anode with high specific capacity and excellent cycling performance.Artificial graphites were prepared using tar coal pitch by carbonizing and graphitizing method. The factors of raw materials, highest heating temperature, heating rate, carbonization temperature, pre-carbonization have been studied to obtain the easy graphitization tar coal pitch coke, and the artificial graphites were prepared after subsequent graphitization. The results show that the artificial graphite prepared by tar coal pitch after a carbonization with a heating rate of1℃/min at700℃has the best cycle performance at low current density. The artificial graphite shows an initial reversible capacity of360.3mAh g-1with a capacity retention rate of98.7%after50cycles. While a pre-carbonization at350℃was added in the optimum conditions above, the artificial graphite achieved the best rate performance with a reversible specifical capacity of319.8mAh g-1at10C.Using graded superfine artificial graphite powder (G,<1μ m), Nano-sillicon(Si,<30nm), heated tar coal pitch(P) and glucose as raw materials, the effects of two methods of adding tar coal pitch on the structure, morphology and electrochemical properties of the composites have been investigated. One is spray drying the mixture of Si,G,glucose and heated tar coal pitch to obtain precursors and subsequent pyrolysis to synthesize the composite.The effects of silicon content, calcination temperature on the structure, morphology and electrochemical properties of Si-G-P/C composites have been studied. It is found that the composite prepared with10wt.%Si and a heat treatment at700℃achieved the best performance. The composite shows an initial reversible capacity of614.1mAh g-1with an initial coulombic efficiency of69.7%,and a capacity retention rate of70.2%after50cycles. The other is synthesizing the Si-G/C composite by spray drying and pyrolysis at first, and then using tar coal pitch coating the Si-G/C composite to obtain the final sample. The effects of binder PVDF and LA123have been studied. It is founded that the composite using PVDF as binder performed better than the composite prepared using the first method. The composite performs better when LA123was used as binder, and achieves an initial discharge capacity of600.2mAh g-1, an initial coulombic efficiency of78.8%and a capacity retention rate of79.1%after50cycles. In addition, the composite possesses good rate performance. Comparatively speaking, the composite prepared by the second method performes better.