Synthesis And Electrochemical Property Of Nanostructured Li-Mn-O Electrode Materials

Based on the nanostructured precursors: MnOOH and Mn₃O₄, Li₂MnO₃ nanoparticles and nanorods were successfully prepared in the temperature range of 500 800℃ through a conventional solid state reaction. Furthermore, a facile oxidation-reduction hydrothermal method was introduced to synthesize monoclinic Li₂MnO₃ and orthorhombic LiMnO₂ with different nanostructures (nanoparticles and nanorods). K₂S₂O₈ and CH₃CH₂OH were chosen as the oxidant and reductant, respectively. With the continuously stirring, LiMn₂O₄ nanoparticles were also successfully prepared via the reaction of Mn₃O₄ with LiOH·H₂O. The samples were characterized by XRD, TEM, ESR and FTIR measurements. With the experimental results, the mechanism of phase evolution has been proposed. The electrochemical properties of the nanostructured Li-Mn-0 electrode materials were studied fundamentally and the realationship between the nanostructures of electrode materials and their electrochemical properties was investigated.The electrochemical property results of Li - Li₂MnO₃ batteries based on Li₂MnO₃ nanorods and nanoparticles indicated that at 25 ℃, the initial charge capacities of the Li - Li₂MnO₃ batteries at high voltage region (4V) were 123mA · hg^-1 and 112mA · hg^-1, respectively and discharge capacities were 104mA· hg^-1 and 89mA· hg^-1, respectively. At the second cycle, the capacities increased a little, but from the third cycle, the capacities decreased. At the fifth cycle, the discharge capacities decreased to 94mA · hg^-1 and 87mA · hg^-1 and the total capacities losses were 12 % and 8 %, respectively.For Li - LiMn₂O₄ battery, the initial charge and discharge capacities were 160mA · hg^-1 and 146mA · hg^-1, respectively, but the discharge voltage was about 2V lower than the reported. For Li - LiMnO₂ battery, the initial charge and discharge capacities were 100mA · hg^-1 and 94mA · hg^-1, respectively. The discharge voltage was about 2.3-3.0 V which was very stable at this range. The results indicate that the Li - LiMnO₂ battery can be used repeatedly for several times.