Study on the structural stability and electrochemical behavior of high voltage LiNi0.5Mn1.5O4 spinel cathode materials based on aluminum site regulation.

At high operating voltages, high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) undergoes serious lattice distortion and Jahn-Teller effect, accompanied by slow Li+ diffusion kinetics, which greatly hinders its practical deployment. Herein, Al-substituted LNMO (LiNi0.5Mn1.5-xAlxO4) was prepared by ion infiltration, and the influences of Al doping on structural and electrochemical performances were comprehensively explored. Combined physicochemical characterizations verify that Al3+ preferentially occupies the 16d crystallographic sites of the spinel lattice. This modification reduces cation mixing and induces a mild lattice contraction, with no secondary phases detected. Electrochemical measurements demonstrate that the optimized LNMO-A0.05 possesses superior rate performance and cyclability. After 100 cycles at 0.2C, it maintains capacity retentions of 95.1% (25 °C) and 89.9% (55 °C). In situ XRD analyses confirm that Al doping effectively suppresses lattice distortion and irreversible phase evolution, switching the electrochemical reaction from a two-phase mechanism to a solid-solution reaction. Electrochemical impedance spectroscopy (EIS) characterizations reveal that Al doping reduces charge transfer resistance and, accordingly, elevates the Li+ diffusion coefficient to 7.91 × 10-16 cm2/s. Further density functional theory calculations demonstrate that the robust Al-O covalent bonds function as structural anchors to reinforce the lattice. Meanwhile, electronic delocalization accelerates ion migration and improves reaction kinetics. The assembled LNMO-A0.05/LTO full cell delivers remarkable performance, demonstrating great potential for practical use.