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

Abstract

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.