The Preparation And Electrochemical Properties Of Modified LiCoO₂ Coated With Nano-carbon

In this paper,after reading a lot of literature,the modification of lithium cobalt oxide(LiCoO2)cathode material for lithium-ion battery was studied by using trace graphene(GR)and carbon nanotubes(CNTs)coating method,and the comprehensive electrochemical properties of GR/LiCoO2 composites,CNTs/LiCoO2 composites and CNTs/GR/LiCoO2 composites were systematically studied.The detail research works are following:LiCoO2 composites were prepared by high temperature solid phase method,and graphene oxide(GO)and carbon nanotubes were micro-controlled,and the GR/LiCoO2,CNTs/LiCoO2 and CNTs/GR/LiCoO2 composites were prepared by ultrasonic dispersion and high temperature reduction methods.The morphology and structure characteristics of the composites were tested by XRD,TEM,SEM,FT-IR methods.The electrochemical properties of the composites were tested by charge and discharge performance test CV,EIS methods.The effects on the structure,morphology and electrochemical properties of GR/LiCoO2 composites were investigated using different mass ratios of graphene oxide(0.4%,0.8%,1.2%,1.6%).The crystal particles of LiCoO2 prepared by high temperature solid phase method are complete,and the addition of graphene does not affect the crystal structure of LiCoO2 composites.The thin-film graphene is encapsulated in the LiCoO2 crystal particles and forms a three-dimensional spatially conductive network structure with them.The electrochemical test shows that the graphene oxide coating with 1.2%addition has the best effect,and the discharge specific capacity is 164.32 mAh/g at 0.1C rate,and still 144.28 mAh/g at 5C rate,GR/LiCoO2 composites polarization and charge transfer impedance decreases,and Li'transport ability enhancement,has better electrochemical reversibility.The electrochemical properties of CNTs/LiCoO2 composites were studied by adding different mass ratios of carbon nanotubes(0.3%,0.6%,0.9%,1.2%).Carbon nanotubes are more evenly distributed on the surface of LiCoO2 crystal particles,the CNTs/LiCoO2 composite with 0.9%carbon nanotubes had the best electrochemical performance.After 100 cycles at the 1C rate,the specific discharge capacity was still 139.54 mAh/g,and the capacity retention rate was 90.14%,at a high rate of 5C,the specific discharge capacity was 138.7 mAh/g.The coating of CNTs improves the overall electrochemical performance of the LiCoO2 composite.Based on the optimal addition of graphene oxide(1.2%),different mass ratios of carbon nanotubes(0.5%,1%,1.5%,2%)were added to modify the LiCoO2 composites.The properties of CNTs/GR/LiCoO2 composite is the best when the addition amount of carbon nanotubes is 1.5%.Graphene and carbon nanotubes are alternately dispersed on the surface of LiCoO2 composite material,which reduces agglomeration to a certain extent.A three-dimensional nanoscale conductive network is formed inside the composite material,which forms an effective conductive pathway between LiCoO2 particles,thus improving the electrochemical performance of LiCoO2 lithium-ion batteries.