Revealing the coupled cation interactions behind the electrochemical profile of Li_xNi_0.5Mn_1.5O₄

We present first-principles energy calculations and a cluster expansion model of the ionic ordering in Li_xNi_0.5Mn_1.5O₄ (0 ≤ x ≤ 1), one of the proposed high-energy density next-generation Li-ion cathode materials. The developed model predicts an intricate relationship between the preferred Li-vacancy ordering and the Ni/Mn configuration, which explains the difference in intermediate ground states between ordered (P4₃32) and disordered (Fdm) Ni/Mn configuration. The phase sequence as a function of lithiation as well as the voltage profile are well matched with experimental results. Understanding of the inherent chemical interactions and their impact on the performance of an energy storage material is essential when designing and optimizing Li-ion electrode materials.