The Synthesis Of New Structrue Metal Oxide/carbon-based Nanocoposites And Their Application As Anode Material For Lithium Ion Batteries

Metal oxides,especially transition metal oxides,are widely used as anode materials in lithium ion battery because of their high theoretical capacity?600?1000 mAh g-1?.However,their own defects lead to limitation in application.For example,transition metal oxide has poor conductivity,the lithium oxide produced during the reaction of the lithium ion battery will further damage the conductivity of the material;The first irreversible capacity loss is great;In the reaction process of lithium ion battery,the electrode material will become larger and the electrode material will be powdery and so on.So in order to solve these problems,in this paper,the battery properties of tin oxide,cobalt oxide and graphene and carbon nanotube composites were explored.The main components are as follows:?1?Graphene nanosheets were obtained by heat treatment of rGO,which were prepared by preoxidation and reoxidation of graphite.Then,stannic chloride,water,ethanol and graphene were used as raw materials,and the SnO₂/rGO composite was o?tained by microwave reaction for 15 min.The experimental results show,that SnO₂ quantumdots with a size of 1?5 nm are uniformly distributed in the reduction of graphene nanosheets.The composite was assembled into a lithium ion serni-cell for testing,and the specific capacity was continue maintained at 797 mAh g-1(After 100 cycles at current density?100,200,400,800 mA g-1?,when the current density switch back to 100 mA g-1,significantly higher than that of the pure SnO₂.The good electrochemical performance is due to the synergistic effect of SnO₂ and graphene.Graphene improves the conductivity of composites and prevents the aggregation of SnO₂ in the reaction process.On the other hand,the quantum dot of SnO₂has the size effect,so that the synthesized material is in full contact with the electrolyte,thus reducing the diffusion path of the lithium ion.?2?SnO₂-CoO/CNT composites were made from Co?Ac?2·4H₂O,NaSnO3,water and multi-wall carbon nanotubes,which were then treated 18 h in a water bath.Through the analysis of SEM,TEM,HRTEM,TG,XRD,XPS and Raman,it was found that SnO₂ and CoO particles were well attached to multi-walled carbon nanotubes.The composite was assembled into a lithium ion semi-cell and characterized its electrochemical properties.The experiment shows that after 100 cycles of constant current density of 100 mA g-1,the specific capacity can still keep in 792 mAh g-1 Such superior electrochemical performance is mainly attributed to:1.The small size effect of SnO₂ and CoO of nano-composite materials increases the activity of the materials in the process of lithiation and de-lithification;2.The synergistic effect of SnO₂ and CoO;3.The synergistic effect of multi-walled carbon nanotubes and SnO₂ and CoO provides a large specific surface area,which reduces the transmission distance of lithium ions in the reaction process.?3?Using SnCl4 ·5H₂O,Co?Ac?2 "4H₂O,NH3·H₂O and rGO as raw materials,the SnO₂-CoO/rGO nanocluster composite materials were obtained by microwave reaction for 15 min and then heat treatment.Assembled the composite in lithium ion battery and took a test of its electrochemical performance,the results show that under the constant current density of 100 mA g-1 after 100 cycles the specific capacity can still keep in 1264 mAh g-1.After cycling at different current densities?100,200,400,800 and 1600 mA g-1?,when the current density is restored to 100 mA g-1 again,the specific capacity is still keep in 1037 mAh g-1.The superior electrochemical properties of the material is mainly due to the following several aspects:1.The rGO has good electrical conductivity and it improves the conductivity of the composite materials in general;2.The cluster structure of SnO₂-CoO facilitates the intercalation and removal of lithium ions in the process of reaction,which is beneficial to increase the efficiency of reaction;3.The SnO₂-CoO cluster structure increases the contact area with electrolyte and reduces the reaction distance of the lithium ion;4.The synergistic effect of SnO₂,CoO and reduced graphene oxide,especially the increase in the capacity of the cyclic late period,is caused by the conversion Co²⁺ to Co³⁺.