Of Limn <sub> 2 </ Sub> O <sub> 4 </ Sub> Urea Assisted Sol-gel Method Synthesis, Modification And Electrochemical Performance

Spinel LiMn₂O₄ was regarded as a substitute for the cathode material of lithium ion batteries, LiCoO₂, due to its many merits such as being friendly to environment, low cost, good electrochemical properties and so on. Although spinel LiMn₂O₄ had some shortness such as low capacity, bad charge-discharge cycle property, fast capacity fading and so on, its electrochemical properties could be improved by new synthetical methods such as sol-gel method, doping and suface coating et.al. In present, the key of researching spinel LiMn₂O₄ is to improve its rechargeable rate capacity, rechargeable life and charge-discharge properties under high temperature. Therefore, it is very important to synthesize LiMn₂O₄ with stable structure and excellent electrochemical properties. The thesis consists of six charpters.In the first charpter, the current survey on the lithium ion batteries materials, especially some synthetical methods of spinel LiMn₂O₄, and supercapacitor were introduced. Meantime, we brought forward the mean of this paper and some problems needed to be solved.In the second charpter, pure spinel LiMn₄O₄ material with good electrochemical properties was prepared by urea-assisted sol-gel method in short time and low temperature. Comparing to the methods reported by literatures, the urea-assisted sol-gel method could make the reaction agents distribute uniformly in molecular level. The spinel LiMn₂O₄ powders yielded by this method had an average particle size of 60 run with narrow distribution and regular spherical morphology, because of the multi-fuction of urea, such as ligand, combustion agent and grain growth controller and so on. And at the same time, the reaction mechanism was studied.In the third charpter, some elements such as Li, Cr, Co, Ni, Mg, Zn, Al, Fe and F were chosen to adulterate to restrain the Jahn-Teller distortion in order to improve the structural stability and electrochemical properties of LiMn₂O₄ powders. Research showed that when the doped amount was 0.1, in the single-doped products the Cr-dope, Ni-dope and Co-dope were better than any others. We also found that co-dope was a better way to improve the electrochemical properties of spinel...