Research On Synthesis And Modification Of Nanostructured LiMn₂O₄ For Lithium-ion Batteries

Spinel LiMn₂O₄ is a new kind of cathode material for lithium-ion battery. Its theoretical specific capacity is 148mAh/g. LiMn₂O₄ has received much attention as a cathode material because of the high voltage required for lithium insertion and its lower price and better compliance with environment and so on. However, LiMn₂O₄ often shows a lower storage capability, its cycle performance at the high rate should be improved. On the base of reviewing the development of lithium ion battery and its cathode materials in detail, LiMn₂O₄ with nanostructure was chosen as cathode material and their synthesis and modification were studied.Hydrothermal synthesis,sol-gel method and wet ball-milling promoted solid state reaction were adopted to prepare nanostructured LiMn₂O₄. The products were investigated by X-ray diffractometer (XRD), Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM). Moreover, we used charge-discharge test to study specific capacity and cycle performance, cyclic voltammogram (CV), electrochemical impedance measurements (EIS) and its equivalent circuit to discuss electrochemical reactive mechanism. The results show that the crystal size of the materials prepared by the above methods reach to nano-grade, particularly, the products obtained by hydrothermal method and wet ball-milling promoted solid state reaction had a much smaller particle size and a narrower particle size distribution and the high rate discharge-capability was improved to a certain extent. Meanwhile, the modified materials were also studied on the basis of LiMn₂O₄ with nanostructure.The study showed that LiMn₂O₄ prepared by hydrothermal method firstly using MnO₂ as precursors had a good electrochemical properties, its initial specific charge capacity was up to 120mAh/g (at 0.2C discharge rate). Wet ball-milling promoted solid state reaction reduced the heating temperature and the sintering time; optimized the synthesing route compared to the traditional solig state reaction to prepare LiMn₂O₄. The electrochemical properties were improved.Finally, we studied the modified materials of nanostructured LiMn₂O₄ (doping and composition), the results indicated that Ag-doped and LiMn₂O₄/carbon aerogels nanocomposite materials can enhance the electronic conductivity efficiently and improve its electrochemical performance; V-doped nanostructured LiMn₂O₄ showed reduced irreversible capacities, improved cycling performance; The addition of VO₂ (B) to LiMn₂O₄ increased the electrochemical window, utilized a large discharge capacity in the 3V region efficentlty, enhanced the specific capacity of the material dramatically.