Understanding the Effect of Al Doping on the Electrochemical Performance Improvement of the LiMn₂O₄ Cathode Material

It is well known that the electrochemical performance of spinel LiMn2O4 can be improved by Al doping. Herein, combining X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) with in situ electron-beam (E-beam) irradiation techniques, the influence of Al doping on the structural evolution and stability improvement of the LiMn2O4 cathode material is revealed. It is revealed that an appropriate concentration of Al3+ ions could dope into the spinel structure to form a more stable LiAlxMn2–xO4 phase framework, which can effectively stabilize the surface and bulk structure by inhibiting the dissolution of Mn ions during cycling. The optimized LiAl0.05Mn1.95O4 sample exhibits a superior capacity retention ratio of 80% after 1000 cycles at 10 C (1 C = 148 mA h g–1) in the voltage range of 3.0–4.5 V, which possesses an initial discharge capacity of 90.3 mA h g–1. Compared with the undoped LiMn2O4 sample, the Al-doped sample also shows superior rate performance, especially the capacity recovery performance.