Synthesis And Modification Of LiMn₂O₄ As Cathode Materials Of Lithium Ion Battery

The principle and the development of lithium ion batteries and the survey of cathode materials have been described in this dissertation. The technics condition, the preparation methods, and some existing problems of LiMn2O4 have been introduced with emphasis. There are two main factors resulting in fading capacity and poor cyclability, one is the John-Teller distortion of Mn3+,and the other is Mn dissolution to electrolyte. The main objects of this paper are to resolved these key problems effecting on the performance of batteries. During the research of suppressing Jahn-Teller distortion, low valence cation (Al,Mg) and anion (F) doped method are usually adopted. On the basis of this, the cathode materials were prepared and their structure and electrochemical performance were investigated in detail.Firstly, the LiMn2O4 samples were prepared by the sol-gel method, and Its electrochemical performance and physicochemical properties was examined in LiMxMn2-xO4/Li cells by Thermogravimetry-Differential Thermal Analysis (TG-DTA), X-ray diffraction (XRD), Scanning Electron Microscope (SEM), galvanostatic charge-discharge test, Electrochemical Impedance Spectroscope (EIS) and cyclic voltammetry (CV). It was found that the LiMn2O4 phase is formed when the precessor is calcined at 350℃, and the pure LiMn2O4 is obtained over 800℃. The discharge capacity increase at first and then decrease with the increase of calcination temperature. The sample calcined at 800℃has larger discharge capacity (123mAh·g-1)Secondly, LiAlxMn2-xO4, LiMgxMn2-xO4, LiAl0.05Mn1.95O4-yFy and LiMg0.1Mn1.9O4-yFy samples were prepared by the sol-gel method and their physical properties and electrochemical performance were investigated by XRD, SEM, XPS, galvanostatic charge-discharge test and CV. The results of electrochemical testing showed that Al, Mg-doped LiMn2O4 had excellent cycle performance. LiAl0.05Mn1.95O4, LiMg0.1Mn1.9O4 showed better capacity retention than LiMn2O4, exhibiting little capacity fade over 50 cycles, even though the first discharge capacity of LiAl0.05Mn1.95O4, LiMg0.1Mn1.9O4 (117mAh·g-1,109 mAh·g-1) were lower than that of LiMn2O4 (123mAh·g-1), at C/5 charge and...