The Investigation Of Electrochemical Properties On Novel Transition Metal Compound/Graphene Composites As Anodes For Lithium Ion Batteries

Nowadays, lithium ion batteries as one of new energy sources have become the highlight of scientific research. The development of portable electronics, power grid, and electric vehicles requires higher demands for lithium ion batteries. One of the most important chanllenges is to improve their capacity and cycling performance. However, the capacity of commercial carbon anode is too low to meet the requirement. Transition metal oxides have attracted much interest for its natural abundant and high theoretical capacity. However, the formation of oxide materials often requires a calcination treatment during the synthetic process. Under such background, transition metal carbonates can be a novel anode for its safety without calcination treatment. In this thesis, we designed different shaped manganese carbonate and ferrous carbonate, respectively, realized their composition with grapheme at low temperature and the obtained composites showed a desired cycling performance and rate performance. The content of research mainly includes two aspects:?1? Synthesis of MnCO₃ nanoplatelets-reduced graphene oxide ?RGO? composites. A novel kind of MnCO₃ nanoplatelets-RGO composites, as an anode material in rechargeable Li-ion battery, has been prepared by a simple low temperature reaction route. The graphene oxide was reduced by hydrazine after MnCO₃ nanoplatelets were added. The graphene not only provided an avenue for the transport of Li-ion, but also buffered the volume expansion of MnCO₃ nanoplatelets during charge and discharge. Compared to pure MnCO₃ nanoplatelets, MnCO₃-RGO composites presented the improved electrochemical performances. At a low current density of 100 mA g^-1, MnCO₃-RGO composites delivered a desired performance of 849.1 mAh g^-1 after 200 cycles. When at a high current density of 500 mA g^-1, the discharge capacity still maintained at 810.9 mAh g^-1 after 700 cycles. Our experimental results suggest that this composite can be a candidate as a novel anode material for the power batteries of electric vehicles and the energy storage batteries of smart grids in the future.?2? Synthesis of Fe₃O₄-RGO composites with broccoli-like FeCO₃ hierarchical microspheres as precursor. The broccoli-like FeCO₃ nanoparticles were synthesized via one-pot hydrothermal process at low temperature. Then the obtained broccoli-like FeCO₃ nanoparticles were mixed with graphene. The graphene oxide was reduced through reflux with hydrazine. During this process, the broccoli-like FeCO₃ precursor hydrolysed and Fe₃O₄-RGO composites were obtained at last. The Fe₃O₄-RGO composites showed an outstanding performance of 890.9 mA h g^-1 at a high current density of 100 mA g^-1. When at a high current density of 500 mA g^-1, the discharge capacity still maintained at 636.1 mAh g^-1. Thus, the broccoli-like FeCO₃ hierarchical microspheres can not only perform as an excellent anode, but also a precursor for iron oxides without high-temperature calcination, which provide a novel avenue for the synthesis of metal oxide materials as Li-ion battery.