Phase Transition Dominated High-Rate Performances of the High Voltage LiNi_0.5Mn_1.5O₄ Cathode: Improvement on Structure Evolution and Ionic Diffusivity by Chromium Doping

Phase transition can profoundly influence the electrochemical performances of cathode materials for lithium ion batteries. The intricate phase transitions upon electrochemical cycling constrain the high-rate performances of the LiNi_0.5Mn_1.5O₄ cathode. The formation of the rocksalt-like phase causes the diffusion of Li ions asymmetric in the lithiation and delithiation reactions. The evolution of multiple cubic phases results in poor diffusivity of Li ions in the LiNi_0.5Mn_1.5O₄. High-resolution XRD scans on the chemically delithiated samples reveal that the intricate phase transitions are effectively suppressed in Cr-doped LiNi_0.5Mn_1.5O₄. The suppression of phase transitions not only enhances the Li ions' diffusivity inside the lattice, but also stabilizes the charge transfer interfaces by reducing lattice mismatch and alleviating structural stress during the lithiation and delithiation. Consequently, the improvement on structure evolution endows the LiNi_0.5Mn_1.5O₄ with enhanced diffusion coefficient of Li ions, larger accessible capacity, and improved Coulombic efficiency.