Preparation And Modification Of Co₃O₄ Anode Materials For Lithium Ion Batteries

Lithium ion battery is considered to be the excellent power source in the development of new energy vehicles because of its advantages of high specific capacity,stable chemical properties,friendly environment,long cycle life and good safety.This paper takes the Co₃O₄ of anode material for lithium ion battery as the research object,aiming at its first low Coulomb efficiency and poor cycle performance.The surface treatment,nano-synthesis,iron-doped and carbon nanotube composite of Co₃O₄ are carried out to improve the comprehensive electrochemical performance of the material.The main work of this thesis is divided into the following aspects:（1）Surface treatment of commercial lithium ion battery anode material Co₃O₄with silane coupling agent using a facile solid phase method.The amorphous Si O₂was uniformly coated on the surface of the Co₃O₄ particles with an average thickness of 5 to 8 nm.The Si O₂ coating did not affect the change of the lattice and morphology of the material.The electrochemical test results showed that the addition of 2wt.%Si O₂ could significantly improve the electrochemical performance of Co₃O₄.Specifically,the charge specific capacity of Co₃O₄ increases by 169.54 and 183.09m A h/g at RT（room temperature）and 55 ^oC at a constant current density of 50 m A/g,respectively.Improved by 1.99 and 2.68 times at RT and 55^oC at high current density of 800 m A/g,respectively.In addition,the charge specific capacity of the coated Co₃O₄ was 1.35 times that of the untreated material after 50 cycles at 55 ^oC.CV and EIS tests showed that the improved performance was mainly attributed to the unique amorphous silica coating on the surface of the material,which effectively reduced the direct contact of the anode material with the electrolyte and inhibited the side reaction between Co₃O₄ and the electrolyte.（2）The nano-scale Co₃O₄ was prepared by hydrothermal coprecipitation method and the first charge/discharge capacity of nanosized Co₃O₄ can reach 1548.62/1091.93m Ah/g,which is much improved relative to commercial Co₃O₄.The particle size of the doping iron material is reduced obviously,in which the material of doped iron with the amount 2 wt.%has the smallest size.The formation of oxygen vacancies provides more space for the diffusion of lithium ions,which also plays an important role in controlling the band structure and carrier concentration,improving the conductivity.Iron-doped 2wt.%lithium-ion battery anode materials have the best comprehensive electrochemical performance:the first discharge/charge specific capacity of the CF-6 sample is 1385.02/1027.06 m Ah/g.After 50 weeks of cycling,CF-6 showed a high reversible capacity of 856.92 m Ah/g,capacity retention is90.58%.（3）The CNTs composite modification of the CF-6(Co_2.94Fe_0.06O₄)showed that CF-6/CNTs composite enhance the electrical conductivity of the electrode material,increase the contact area and specific surface area between the electrode and electrolyte of the nanocomposite,buffer the volume expansion of the material during the charge-discharge process,reduce the resistance of the material and increase the transfer rate of electrons during the charge-discharge process.The composite exhibits high charge specific capacity at current densities of 50 m A/g and 800 m A/g,shows good rate performance at 100 m A/g current density cycle of 50 cycles,its reversible charging specific capacity can reach 1267.46 m Ah/g,showing excellent cycling performance.