Revisiting the Temperature-Dependent Phase Structure of Spinel LiNi_0.5Mn_1.5O₄ for Lithium-Ion Batteries

To optimize the high-voltage spinel cathode LiNi0.5Mn1.5O4 (LNMO), understanding the influence of different phase composites (i.e., the Fd3m and P4(3)32 phases) on its electrochemical performance is essential. This study investigates the phase ratio of the Fd3m phase and P4(3)32 phase spinel structures in LNMO as influenced by the calcining temperature using neutron powder diffraction and X-ray powder diffraction (XRD). The coexistence of the Fd3m and P4(3)32 phases in the LNMO products is found to be temperature-dependent. In situ XRD and Raman analyses reveal that LNMO products with a higher proportion of the Fd3m phase exhibit improved ion-transport efficiency but also suffer from increased Mn3+ solubility and subsequent irreversible capacities, limiting battery cycling stability. In situ variable-temperature XRD identifies an optimal synthetic temperature range for LNMO, facilitating the synthesis of materials with the desired phase proportions and crystal structures.