Synthesis And Modification Of Cathode Materials For Lithium-ion Battery

Lithium ion batteries are getting more and more attention along with its widespread use in our daily life. However, the sufficient energy storage capacity is still a problem which prevent its high capacity application. So it is necessary to develop new cathode material or modification to exist material to meet the requirement for such applications. The main contents of our research is as follows:(1) Well formed cathode materials of serial 0.6Li[Li1/3Mn2/3]O2-0.4Li Ni(2+x)/6Mn(2+x)/6Co(1-x)/3O2(X=1, 3/4, 1/2, 1/4, 0) are synthesized by a spray drying method. X-Ray diffraction(XRD) 、 Scanning electron microscope(SEM) and High resolution transmission(HTEM) are used to characterize the structure and micromorphology of the material. Meanwhile, charge-discharge tests,and Cyclic Voltammetry(CV) are employed to investigate the influence of cobalt content on the electrochemical performance. The results indicate that with the increase of Co, the inhibition of cationic mixing makes the atoms are arranged to be orderly structured. The introduction of the electrochemical performance, Co make more Li2 Mn O3 activated, which will lead a higher initial specific capacity, but due to the irreversible reaction, the first coulomb efficiency is not high, material with low Co content have a good cycle stability, after 50 cycles capacity basically remains the same, while more Co will make steady performance declined. Li[Li0.2Ni0.17Mn0.56Co0.07]O2 coated with Zn O(1.5wt%) was prepared by sol–gel method,The results demonstrate that Zn O coating can effectively obstruct the contact between cathode electrode and the electrolyte, and improve the cycling stability of the material.(2) The ideal Li Ni0.5Mn1.5O4 cathode materials for lithium ion battery are considered with properties of good cyclic stability, rate capability and high average voltage. Those properties required material of disordered structure and low oxygen deficiency. However, Li Ni0.5Mn1.5O4 with disordered Fd 3-m symmetry usually accompanied with oxygen deficiency. The post-annealing treatment at 650–700 for 48 h can efficiently suppress the oxygen deficiency of Fd3-m structure, but meanwhile it would change to P4332 and loss the advantage of high rate capability. Fortunately, on the basis of Kim’s work about Li Ni0.5Mn1.5-xTixO4(0.1≤x≤1.0), high voltage cathode Li Ni0.5Mn1.35Ti0.15O4 with Fd3-m structure and low oxygen deficiency have been successfully synthesized in this work. The structure and oxygen deficiency of material were effectively controlled by means of the combination of Pre/Post-doping lithium method with urea combustion post-treatment. The modified material possesses a long voltage platform around 4.7 V and good rate capability with 82% capacity retention at 40 C. Moreover, with the help of urea combustion post-treatment, it only needs 5h to repair the oxygen deficiency in this work.