Synthesis Of Ordered Mesoporous Carbon Compsites And Its Electrochemical Properties

Ordered mesoporous carbon (CMK-3) has high specific surface area, uniform pore size, ordered channel and good conductivity, etc., and has also considered as a promising carbon matrix for fabricating electrode in Li-ion batteries. In this dissertation, CMK-3 was chosen as a carbon matrix material for preparing carbon-based composites via a self-assembly solvent evaporation and hydrogen reduction route. The effects of reaction contiditions on the phases, crystal structures of final products were also investigated in detail. Furthermore, these composites electrochemical properties were used as the anodes in Li-ion batteries, and the relationships between these materials and electrochemical properties were also explored. The main contents and results are as follows:(1) A series of Sn-Cu-CMK-3 composites with different carbon contents were successfully synthesized for the first time. It was found that two phases of CueSn5 and Cu3.02Sn0.98 were formed when the carbon content was 33% in the composites, and their crystalline were high. Furthermore, these materials were used to fabricate Li-ion batteries and their electrochemical properties were investigated. It was found that the cell made of the composite with 33% carbon content exhibited higher reversible specific capacity and cycling stability at 0.1 and 0.5 A g-1, which is also better than those of the samples CMK-3 and Sn-Cu alloy. Thus, the electrochemical performance can be enhaced when CMK-3 was used as a composite in anode materials. CMK-3 has ordered mesoporous structure, and not only can be effectively buffered volume expansion of Sn-Cu particles during the cycle, but also can increase the contact area between Sn-Cu particles and the electrolyte, and short the transmission path lithium ion and electron, thus, leading to the improved electrochemical properties of the composite.(2) The composites of Sn-Co-CMK-3 with different ratios of Sn/Co were synthesized at different temperatures, and then used as anodes for Li-ion batteries. It was found that the sample with a Sn/Co ratio of 5 synthesized at 550 ℃ exhibited a large reversible capacity, high rate performance and cycling stability. For instance, a reversible capacity of 562 mAh g-1 was maintained after 60 cycles at 0.1 A g-1. The enhanced electrochemical properties migh be attributed to the facts that CMK-3 was selected as a composite material.(3) The composite of MoS2-CMK-3 was successfully prepared with phosphomolybdic acid and thiourea at different temperatures. XRD indicated that MoS2-CMK-3 synthesized at 800℃ have higher crystallinity. Using this material as an anode in Li-ion batteries, a discharge specific capacity was matained 606 mAh g-1 at 0.1 A g-1 after 45 cycles, which is higher than that of CMK-3 and MoS2, indicating that the electrochemical properties were improved greatly. This migh be attributed to the facts that the conduction of the composite has been greatly improved for the introduction of CMK-3.