Removing the Two-Phase Transition in Spinel LiMn₂O₄ through Cation Disorder

Resource constraints have become critical for the Li-ion industry. Spinel LiMn<sub>2</sub>O<sub>4</sub> presents a cheaper, more sustainable alternative to traditional layered Li-ion cathodes, but its capacity is constrained by a two-phase transition at 3 V associated with large, inhomogeneous volume change leading to capacity loss. In this Letter, we argue that disorder can replace the two-phase region with solid-solution behavior to create high-capacity cathodes. By investigating the voltage curve and lithiation pathway of LiMn<sub>2</sub>O<sub>4</sub> spinel with varying levels of Mn disorder, we find that disorder shortens the 3 V plateau by raising the energy landscape and stabilizing motifs found in solid-solution configurations. The plateau disappears completely with 25% Mn 16c occupancy. These results provide guidance on the optimal level of disorder in spinels to achieve both solid-solution behavior and good Li mobility and also highlight more generally how disorder can be utilized to reduce the effects of problematic phase transformations in ordered frameworks.