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.