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

Abstract

To optimize the high-voltage spinel cathode LiNi 0.5 Mn 1.5 O 4 (LNMO), understanding the influence of different phase composites (i.e., the Fd3̅ m and P4 3 32 phases) on its electrochemical performance is essential. This study investigates the phase ratio of the Fd3̅ m 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 Fd3̅ m 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 Fd3̅ m phase exhibit improved iontransport efficiency but also suffer from increased Mn 3+ 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.