Variations of the Electrochemical Properties of LiMn2O4with the Calcining Temperature

Abstract

LiMn₂O₄ compounds were synthesized by calcining a mixture of LiOH and MnO₂(CMD) at 400℃ for 10 h and then calcining again at 650℃ to 900℃ for 48 h in air with intermediate grinding. All the synthesized samples exhibited XRD patterns for the cubic spinel phase with a space group Fd3m. The lattice parameter increased gradually as the sintering temperature rose. The electrochemical cells were charged and discharged for 20 cycles at a current density 300 ㎂/㎠ between 3.5V and 4.3V. The voltage vs. discharge capacity curves for all the samples showed two plateaus. The LiMn₂O₄ sample calcined at 900℃ had the largest first discharge capacity. This sample exhibited the best crystallinity, had relatively large lattice parameter and had relatively large particles with relatively homogeneous size. All the samples showed good cycling performances. Among all the samples, the LiMn₂O₄ calcined at 850℃ had relatively large first discharge capacity and very good cycling performances. The addition of excess LiOH and the mixing in ethanol considered to help the formation of the more LiMn₂O₄ phase per unit weight sample and the more stable LiMn₂O₄ phase. These led to the larger discharge capacities and the better cycling performances. The cyclic voltammograms for the second cycle of the LiMn₂O₄ samples showed the oxidation and reduction peaks around 4.05V and 4.18V and around 4.08V and 3.94V, respectively. The larger first discharge capacity of the sample calcined at the higher temperature is related to the larger lattice parameter.