Operando X-ray diffraction analysis of the degradation mechanisms of a spinel LiMn2O4 cathode in different voltage windows

The understanding of reaction mechanisms of electrode materials is of significant importance for the development of advanced batteries. The LiMn2O4 cathode has a voltage plateau around 2.8 V (vs. Li+ Li), which can provide an additional capacity for Li storage, but it suffers from a severe capacity degradation. In this study, operando X-ray diffraction is carried out to investigate the structural evolutions and degradation mechanisms of LiMn2O4 in different voltage ranges. In the range of 3.0-4.3 V (vs. Li+/Li), the LiMn2O4 cathode exhibits a low capacity but good cycling stability with cycles up to 100 cycles and the charge/discharge processes are associated with the reversible extraction/insertion of Li+ from/into LixMn2O4 (0 <= x <= 1). In the range of 1.4-4.4 V (vs. Li+/Li), a capacity higher than 200 mAh/g is achieved, but it rapidly decays during the cycling. The voltage plateau around 2.8 V (vs. Li+/Li) is related to the transformation of the cubic LiMn2O4 phase to the tetragonal Li2Mn2O4 phase, which leads to the formation of cracks as well as the performance degradation. (C) 2019 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.