LiMn2O4 cathode doped with excess lithium and synthesized by co-precipitation for Li-ion batteries

LiMn2O4 exhibits lower cost, acceptable environmental characteristics, and better safety properties than other positive-electrode (cathode) materials for lithium-ion batteries. In this study, excess Li doped Li1+xMn2O4 is synthesized by a well-mixed co-precipitation method with LiOH utilized as both the reactant and co-precipitation agent. The precursor is calcined for various heating times and temperatures to form a fine powder of a single spinel phase with different particle sizes, size distributions, and morphology. The minimum heating temperature is around 400 degreesC. For short heating periods, Mn2O3 impurity is observed, but disappears after longer heating times. The average particle size is in the range 2-8 mum for powders calcined between 700 and 870 degreesC. The lattice parameter increases with increase in heating temperature. The electrochemical behavior of LiMn2O4 powder is examined by using test cells which consist of a cathode, a metallic lithium anode, and an electrolyte of 1 M LiPF6 in a 1:1 (volume ratio) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC). Cells with cathodes of LiMn2O4, Li1.08Mn2O4 and Li1.1Mn2O4 give a capacity of 85, 109 and 126 mAh g(-1), respectively. The introduction of excess Li in LiMn2O4 apparently increases the capacity, and decreases significantly the rate of capacity degradation on charge-discharge cycling. (C) 2002 Elsevier Science B.V. All rights reserved.