A Study On The Synthesis Of The Single Crystalline LiMn₂O₄and The Modification Of LiMn₂O₄by Ion Doping

Spinel LiMn2O4has a theoretical capacity of148mAh g-1and high dischargeplateau of3.9V and4.1V(vs Li+/Li) because of its three-dimensional crystalstructure. Spinel LiMn2O4is also a promising candidate to replace layered Ni or Cooxide materials as cathode in Li-ion batteries due to its low cost, environmentalfriendliness, high abundance, and better safety. Spinel LiMn2O4has poor cycleabilitybecause of the dissolution of Mn3+and the Jahn-Teller distrotion. Preparation of thesingle crystalline and ion-doping LiMn2O4materials play an important role in solvingthis problem.The single crystalline spinel LiMn2O4was synthesized by melt-impregnationmethod with the precursor β-MnO2and LiOH. The β-MnO2was prepared fromMn(CH3COO)24H2O and Na2S2O8by hydrothermal reaction. Based on TGA/DTAanalysis, the optimal calcination temperature is fixed, which is at470℃for5h, thenheated to750℃and held for12h. The infuence of the sintering process onproperties of single crystalline LiMn2O4has also been investigated. XRD, FTIR andSEM results demonstrate the uniform particles and good crystallinity of singlecrystalline spinel LiMn2O4nanorods. The single crystalline LiMn2O4obtained byMelt-impregnation method exhibits a superior electrochemical performance, whichdelivers an initial specific capacity of126mAh g-1and91%capacity retention at the100th cycle in the potential range of3.0to4.4V (vs. Li/Li+).The LiNi0.5Mn1.5O4and LiCuxMn2-xO4perpared by coprecipitation method haswell crystallinity and morphology. The influence of the different precipitant on theproperties of the LiNi0.5Mn1.5O4has been studied. The curves of CV show that moreNi was deposited and into the lattice of the LiNi0.5Mn1.5O4with the NH4HCO3asprecipitant, which is also good for the cycle performance of the LiNi0.5Mn1.5O4. TheLiCuxMn2-xO4was also synthesized by coprecipitation method, The influence of thedoping content and the reaction temperature on the morphology and properties of theLiCuxMn2-xO4has been studied. The results of XRD and SEM demonstrate that themorphology of LiCuxMn2-xO4changes from the nanorods to the octahedron as thereaction temperature increased. The crystallinity of LiCuxMn2-xO4also changes at different reaction temperature, and it has the best crystallinity at750℃. The firstdischarge capacity of the LiCuxMn2-xO4decreases in spite of the cycle performancetened to be stable as the doping content increased. The LiCuxMn2-xO4has the bestelectrochemical properties with the Cu-doping content of0.05.