Revisiting the Temperature-Dependent Phase Structure of Spinel LiNi0.5Mn1.5O4 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 Fd3̅m and P4332 phases) on its electrochemical performance is essential. This study investigates the phase ratio of the Fd3̅m phase and P4332 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 Fd3̅m and P4332 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 Fd3̅m 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.