Research On Synthesis Andmodification Of LiNi_1/3Co_1/3Mn_1/3O₂ And LiMn₂O₄ As Cathode For Li-ion Batteries

With high power density and long service life,lithium ion batteries has showed broad prospects applied at electric products and Electric Vehicle and HybridElectric Vehicle.The layered oxides such as LiCoO₂,LiNiO₂,LiNi_1/3Co_1/3Mn_1/3O₂ and Li Mn₂O₄ have been great succesful in commercialization for lithium ion batteries materials.Among them,spinel LiMn₂O₄ is considered to be one of the most promising candidates due to its easy preparation,low cost,safety,nontoxicity and high work voltage.Spherical micro particles due to its high tap density are significance for the assembling of high power batteries.In recent years,research showed that the nanoparticles can improve the power density for its short distance transport.As research objects,Spherical micro LiNi_1/3Co_1/3Mn_1/3O₂ and LiMn₂O₄ and nano LiMn₂O₄particles were parepared by control the precusor or surface modification,The main results are concluded as follows:（1）The preparation of high energy density spherical spinel lithium manganese oxides and modify it by surface coating.First,we prepared spherical MnCO₃ precursor with good dispersity and high tap density by co-precipitation method,The diameter of precursor is about 2μm,then,product Al（OH）₃ precipatition on the precursor surface before calcinate it at high temperature to obtain the spherical spinel LiMn₂O₄.we research on the morphology,structure and electrochemical performance influenced by coating Al³⁺surface.The electrochemical performance measurment results show that the cycling performance of the spherical spinel LiMn₂O₄ improved though the initial charge and discharge performance drop down.The charge-discharge of the curves shows that althongh the initial discharge specific capacity reduced down 13.6 mAhg^-1,the retention of specific capacity improved from 78.9%to 94.1%.（2）The preparation of spherical cathode LiNi_1/3Co_1/3Mn_1/3O₂ in micron diameter.We used the controlable crystallization method,control the reaction process technology conditions strictly to get the spherical LiNi_1/3Co_1/3Mn_1/3O₂ with diameter about 15μm,we also observed the precursor LiNi_1/3Co_1/3Mn_1/3O₂ at different time to study the nucleate and the growth process.Then calcinate it at high temperature to got good dispersion and liquidity spherical LiNi_1/3Co_1/3Mn_1/3O₂ which keep the same size and morphology with the precursor.Electrochemical performance curves show that the initial discharge specific capacity of the LiNi_1/3Co_1/3Mn_1/3O₂ positive materials was up to 164.8 mAhg^-1 at 0.1 C and 134.6 mAhg^-1 at 10 C.（3）The preparation of nano scale spinel LiMn₂O₄.The high crystallinity nano scale spinel LiMn₂O₄ was prepared by sol-gel method with the citric acid as the chelating agent.The average size of the particles were in 150 nm.The result shows that,the amount ratio of citric acid and Mn²⁺will affect the crystallization degree and the electrochemical properties of spinel LiMn₂O₄.The XRD pattern and SEM images shows that when n（citric acid）/n(Mn²⁺)=0.9,the crystallization degree of spinel LiMn₂O₄ was higher than that of others.It is the typical spinel crystallization with the clearly shape and the anisotropy were good.The high degree crystallization can slow down the process of the structure change when charging or discharging,be helpful for Li⁺insert and emergence free.The electrochemical performance curve also showed that the initial discharge specific capacity of the product was 125.6 mAhg^-1,the efficiency was 91.3%at 0.2 C and the initial discharge specific capacity was up to108.7 mAhg^-1 at 1 C.