Research On Synthesis And Property Of Materials For Power Lithium-Ion Battery

Spinel LiMn2O4is deemed to have a wide range of application prospects, owning to many merits, such as simple preparation technology, abundant raw materials, higher working voltage and friendly to environment. The Mn3+in the spinel LiMn2O4bears the Jahn-Teller effect which leads to destroy the spinel structure stability during the process of Li+intercalation and deintercalation. This is because of the tensile and compress deformation, which has bad influence on the electrochemical property. In order to improve its electrochemical property, the multi-cation doping, the cation and anion complex doping and the rare-earth ion doping were used to modify the spinel LiMn2O4in this paper. The results of this study are summarized as follows:1) The Li, Al, Mg and Zn were used to co-dope into spinel LiMn2O4by sol-gel method used citric acid as chelant. At lower sintering temperature, the nano-size Li1.03MMn1.91O4(M=Zn0.03Mg0.03, Al0.03Zn0.03, Al0.03Mg0.03, Al0.03Mg0.015Zn0.015) cathode materials have been successfully synthesized, and the average particle size is smaller than100nm.The multiple cation doping can effectively restrain capacity decrease during cyclic process, therefore the cycle capability can be improved significantly. At room temperature, and the charge-discharge rate of1/3C, the spinel Li1.03Al0.03Mg0.03Mn1.91O4has the largest initial discharge capacity,117.8mAhg-1. Although the theoretical capacity of Li1.03Zno.03Mgo.03Mn1.91O4is low, the initial discharge capacity is close to its theoretical capacity and the capacity retention rate of it after40cycles is the largest, which can reach to97.3%. Li1.03Al0.03Mg0.015Zn0.015Mn1.91O4shows good rate capability at room temperature and elevated temperature.2) On the basis of the cation and anion complex doping, this paper expound the relation between the ratio of Li/Mn and the electrochemical property of the spinel LiMn2O4. As the ratio of Li/Mn increases, the crystal cell parameters decrease gradually, which is in favor of enhancing the stability of crystal structure. After charging potential increase, the Warburg impedance of the Li1.03Zn0.03Mg0.03Mn1.94O3.95F0.05has got somewhat change.This is because the structure of cathode material begin to change during the charging process. Its oxidation and reduction peaks shifft to high potential. The spinel LiAlo.03Mg0.03Mn1.91O4Fo.05has excellent electrochemical property. At the charge-discharge rate of1/3C, the initial discharge capacity is118.2mAhg-1, and the capacity retention after40cycles is95.4%.55℃, the capacity retention after40cycles is88.0%at1/3C.3) In the view of improving the cycle capability and rate capability, the Li, Ce, La, Nd and Y were used to dope into spinel LiMn2O4. Due to the ionic radius of rare-earth elements are much larger than Mn3+, which can play a role of a pillar in the crystal lattices and restrain structure collapses by buffering crystal cell volume change.The impurity phase formation of the Li1.03CexMn1.97-x04is not noly relation to the value of x, but also relation to calcination temperature.Among the R-O(Ce, La, Nd and Y), the bonding energy of La-0is the largest.Therefore the Li1.03Lao.02Mn1.95O4has a good cycle capability and rate capability. At the charge-discharge rate of1/3C, the initial discharge capacity is118.3mAhg-1, and the capacity retention after40cycles is96%, the capacity retention after220cycles is92.8%at1C.