Preparation And Electrochemical Properties Of Nitrogen-Sulfur Doped Carbon/Cobalt Oxide Composites

Comparing with the traditional carbon material,cobalt oxide as a lithium-ion battery anode material has a high theoretical capacity,low cost and environmental advantages.During the charge and discharge cycles,its volume expansion and particle aggregation are serious,which result in poor electrochemical stability and cycling performance.The doping or coating of the carbon material can increase its conductivity and electrochemical performance.In this paper,via doping CoO with conductive polymer carbonized materials,one lithium-ion battery anode which has excellent electrochemical performance is obtained.The main contents of this thesis are as follows:（1）Co（CO₃）_0.5（OH）·0.11H₂O needle-like nanorods were synthesized by self-sacrificial templates to obtain a novel coaxial CoO@N-doped carbon nanotube material with a hierarchical pore structure（HP CoO@NC Nt）.The preparation process is simple,efficient and to be operated.Nitrogen-doped carbon materials with slit pores form a uniform coating on the surface of CoO nanotubes.Due to the nitrogen carbon shell and layered pore structure of HP CoO@NC Nt,the final HP CoO@NC Nt exhibits excellent cycling stability and high rate performance as the lithium ion batteries anode electrode material.Even at a high current density of 2000mA g^-1,a reversible capacity maintains 523.4 mAh g^-1 after 1000 cycles and a capacity retention rate of HP Co O@NC Nt is up to¹00%（2¹000）.This work can provide new ideas for the storage and application of other oxide materials.（2）CoO/Co/N-doped carbon-based（NCm）composites with special sea urchin structure were successfully prepared by one pot hydrothermal method.The PANI chain was used as template and carbon（nitrogen）source.The preparation method is simple and easy.The EDX results show that the nitrogen-doped carbon matrix and the metal Co are uniformly distributed throughout the structure.NCm provides high conductivity and buffers the volume expansion during charge/discharge.Due to the inclusion of nitrogen-doped carbon matrix and Co,CoO/Co/NCm composites exhibit excellent cycling stability at high rate as lithium ion batteries anode electrode.Even under the current density of 5A g^-1 test,after 1000 cycles,the reversible capacity is up to 811.2mAh g^-1,coulomb efficiency is about 100%.The porous CoO/Co/NCm anode electrode can be used for large-scale applications of secondary batteries.（3）CoO@S-doped carbon nanorode（CoO@SC Nr）composites were synthesized by in-situ polymerization of polythiophene intermediates and then annealing.Polythiophene as a source of sulfur and carbon sources can increase the conductivity of CoO@SC Nr anode materials and stabilize their structure to improve electrochemical performance.CoO@SC Nr anode material in the current density of up to 2000 mA g^-1,after 700 cycles,the reversible capacity is still up to 511.3 mAh g^-1.This work is the first application of polythiophene carbonized material as sulfur source and carbon source and cobalt oxide composite,this program can provide some guidance for other transition metal oxide value.