Abstract
LiMn2O4 exhibits lower cost, acceptable environmental characteristics, and better safety property than other cathode materials. In this study, excess Li doped Li1+xMn2O4 and Cr doped LiCryMn2-yO4 were synthesized by well-mixed co-precipitation method with LiOH utilized as both the reactant and co-precipitation agent. The precursor was calcined under various heating time and temperature to form fine powder of single spinel phase with different particle size, size distribution, and morphology. The minimum heating temperature was evaluated around 400□C owing to TG/DTA analysis. The pure spinel LiMn2O4 with excess-Li and Cr-doped were successfully obtained by co-precipitation method and the structure was confirmed by XRD along with the composition measured by ICP-AES. For short period of heating time, the Mn2O3 impurity was observed in lithium manganese oxide synthesized without Cr-doped, however it would disappear after longer heating time. By contrast, pure Cr-doped LiCryMn2-yO4 without impurity could be derived at even lower temperature. From FESEM image and Laser Scattering measurements, the average particle size is in the range of 2-8□m for powders calcined between 700□C and 870□C. The lattice parameter would increase with the elevated heating temperature and decrease with the Cr content. The electrochemical behavior of LiMn2O4 powder was examined by using two-electrode test cells consisted of a cathode, metallic lithium anode, and an electrolyte of 1M LiPF6 in a 1:1 (volume ratio) mixture of EC/DMC. Cyclic charge/discharge testing of the coin cells, fabricated by LiMn2O4, Li1.08Mn2O4 and Li1.1Mn2O4 showed the high capacity of 85, 109 and 126 mAh/g, respectively. LiCr0.05Mn1.95O4 and LiCr0.08Mn1.92O4 powders provide values of 108 and 106 mAh/g, respectively, and both remained 93.5□ of its origin value after 15 cycles. The introduction of excess Li in LiMn2O4 apparently increased the capacity, and the Cr-doped LiMn2O4 significantly decreased the decay rate after cyclic test.