Kristin A. Persson Lawrence Berkeley National Laboratory 1 Cyclotron Rd, MS 62-323 Berkeley CA 94720 USA E-mail: kapersson@lbl.gov The high-voltage spinel is an interesting candidate for Li-ion battery applications. Depending on the synthesis temperature, the material exhibits two different arrangements; a ‘disordered’ Mn/Ni version synthesized at high temperature and an ‘ordered’ material with a predominately ordered cation arrangement. This study presents comprehensive first-principles modeling results and comparison to experiments on the coupling between the cation ordering and phase behavior as a function of delithiation in the high-voltage LixNi0.5Mn1.5O4 (0 < x < 1) spinel. The developed cluster expansion model elucidates an intricate relationship between the preferred Li-vacancy ordering and the Ni/Mn configuration, which explains the difference in intermediate ground states and resulting voltage profile between the ordered and disordered Ni/Mn configurations. We quantitatively demonstrate the incommensurateness between the preferred Li/VA configuration and the Ni/Mn configuration in the ‘ordered’ cation material and show a striking dependence between the range of the solid-solution phase domain and the Ni-Mn cation ordering, as a function of Li content and temperature which correlates with observed performance differences. The perfectly ordered LixNi0.5Mn1.5O4 spinel resists solid-solution until very high temperatures but introducing various degrees of Ni/Mn cation disorder results in a dramatic increase in solid solution stability and a possibility for tuning a desirable single-phase reaction, particularly at high Li content.
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