Variations of the electrochemical properties of LiMn2O4 with synthesis conditions

LiMn2O4, samples were prepared by solid-state reaction at various temperatures between 650 and 900 degrees C from LiOH and MnO2 (chemical manganese dioxide, CMD). Other samples were also prepared at 750 degrees C with a different cooling rate, or for different periods of time (24 and 72 h), with the other conditions being identical. X-ray diffraction patterns of the prepared samples are identified as the spinel structure with a space group Fd (3) over bar m. The lattice parameter increases gradually as the sintering temperature rises. The potential vs. lithium ion concentration curves exhibit two distinct plateaus. The sample sintered at 750 degrees C for 48 h (intermediately cooled at a cooling rate of 1 degrees C/min) has the largest fist discharge capacity and shows the best cycling performance. It is believed that the best electrochemical properties of this sample result from its crystallinity and its large grain size as compared with other samples. The particles of this sample are relatively large and uniform in size. To investigate the crystallinity of the prepared samples, we introduced a "crystallinity index" I-max/B, where I-max is the maximum intensity of a diffraction peak considered and B is the width at an intensity equal to half I-max. (C) 2000 The Electrochemical Society. S0013-4651(99)06-116-9. All rights reserved.